Existing Annotations Review

GO Term	Evidence	Action	Reason
GO:0004055 argininosuccinate synthase activity	IBA GO_REF:0000033	ACCEPT	Summary: Phylogenetically inferred core molecular function. This is the correct and well-supported catalytic activity for ASS1 (EC 6.3.4.5), the enzyme name itself, and is confirmed by direct enzymology of the human recombinant protein. Reason: IBA at exactly the right level of specificity for the family and directly corroborated by human experimental data. This is a defining core function. Supporting Evidence: PMID:8792870 Argininosuccinate synthetase (ASS) is a urea cycle enzyme with a tetrameric
GO:0005829 cytosol	IBA GO_REF:0000033	ACCEPT	Summary: Phylogenetically inferred cytosolic localization. ASS1 is a soluble cytosolic enzyme; the substrate citrulline is exported from mitochondria and converted in the cytosol. Reason: Consistent with UniProt subcellular location (Cytoplasm, cytosol) and with direct immunofluorescence/experimental evidence. Correct compartment for a core function.
GO:0006526 L-arginine biosynthetic process	IBA GO_REF:0000033	ACCEPT	Summary: Phylogenetically inferred role in L-arginine biosynthesis. ASS1 with ASL performs the two steps that convert citrulline to arginine, making arginine available in most tissues. Reason: Core biological process, matching UniProt PATHWAY annotation (L-arginine biosynthesis, step 2/3) and experimental patient/expression data. IBA at appropriate specificity. Supporting Evidence: PMID:8792870 Argininosuccinate synthetase (ASS) is a urea cycle enzyme with a tetrameric
GO:0000050 urea cycle	IBA GO_REF:0000033	ACCEPT	Summary: Phylogenetically inferred participation in the urea cycle, the metabolic step condensing citrulline and aspartate to argininosuccinate. This is a core biological process for the hepatic enzyme. Reason: Well supported by human enzymology and disease genetics; ASS1 deficiency is the cause of citrullinemia type I, a urea cycle disorder. IBA correct. Supporting Evidence: PMID:8792870 Argininosuccinate synthetase (ASS) is a urea cycle enzyme with a tetrameric
GO:0004055 argininosuccinate synthase activity	IEA GO_REF:0000120	ACCEPT	Summary: Automated (multiple IEA methods) assignment of the core catalytic activity, backed by InterPro signatures, RHEA:10932 and EC 6.3.4.5. Fully consistent with the experimental activity. Reason: Redundant with the IBA/IMP argininosuccinate synthase activity annotations but correct; the EC/RHEA/InterPro mapping is accurate for this enzyme. Supporting Evidence: PMID:18473344 caused by deficiency of the urea cycle enzyme argininosuccinate synthetase
GO:0005524 ATP binding	IEA GO_REF:0000002	ACCEPT	Summary: InterPro2GO mapping of ATP binding. ASS1 uses ATP as a co-substrate (activating citrulline via a citrullyl-AMP intermediate), and UniProt documents an ATP-binding SSGGxDS motif and ATP-binding feature/keyword. Reason: Correct molecular function supported by the catalyzed reaction (ATP -> AMP + PPi) and by UniProt nucleotide-binding features; a genuine ligand-binding activity underpinning catalysis.
GO:0005829 cytosol	IEA GO_REF:0000044	ACCEPT	Summary: Subcellular-location keyword mapping to cytosol from UniProt SL-0091. Reason: Consistent with the experimentally supported cytosolic localization; redundant but correct.
GO:0006526 L-arginine biosynthetic process	IEA GO_REF:0000120	ACCEPT	Summary: Automated assignment of the L-arginine biosynthetic process, matching UniPathway UPA00068. Reason: Correct core process, redundant with the IBA/IMP annotations.
GO:0005515 protein binding	IPI PMID:12620389 Novel raf kinase protein-protein interactions found by an ex...	REMOVE	Summary: IntAct-curated interaction with ARAF (Raf kinase) found in an exhaustive yeast two-hybrid screen. "protein binding" is uninformative and this is a high-throughput two-hybrid hit with no established biological consequence for ASS1. Reason: Per curation guidelines, bare "protein binding" (GO:0005515) is uninformative and should be avoided. The interaction is a screen-derived putative binary interaction (A-Raf/C-Raf Y2H atlas) not connected to ASS1 function; it adds no functional information to the review. Supporting Evidence: PMID:12620389 We have performed an exhaustive unbiased yeast two-hybrid analysis to identify
GO:0005515 protein binding	IPI PMID:17496144 Restructuring of the dinucleotide-binding fold in an NADP(H)...	REMOVE	Summary: IntAct-curated interaction with NMRAL1 (HSCARG, an NADP(H)-sensing redox protein). UniProt records this interaction, and NMRAL1 has been reported to regulate ASS1 activity. However the GO term captured is only the uninformative "protein binding". Reason: Bare "protein binding" is uninformative and discouraged. The underlying NMRAL1 interaction is real and biologically noted (redox regulation of ASS1), but the informative content belongs in a specific term or in the description, not in GO:0005515. The interaction itself is retained conceptually via UniProt SUBUNIT and is not lost. Supporting Evidence: PMID:17496144 may be argininosuccinate
GO:0005515 protein binding	IPI PMID:28587924 PRMT7 Interacts with ASS1 and Citrullinemia Mutations Disrup...	REMOVE	Summary: IntAct-curated interaction with PRMT7 (protein arginine methyltransferase 7), a direct interactor identified by Y2H and confirmed by pull-down; citrullinemia mutations disrupt the interaction. Captured only as uninformative "protein binding". Reason: Bare "protein binding" is discouraged. The PRMT7-ASS1 interaction is a genuine and interesting finding, but the GO term is uninformative; the biology is retained in the description and could be captured by a specific term if warranted. No functional information is lost by removing GO:0005515. Supporting Evidence: PMID:28587924 interacts with ASS1 using pull-down studies.
GO:0042802 identical protein binding	IPI PMID:16189514 Towards a proteome-scale map of the human protein-protein in...	ACCEPT	Summary: Self-interaction (ASS1-ASS1) consistent with the well-established homotetrameric quaternary structure of the enzyme. Reason: "identical protein binding" is informative here: ASS1 is a homotetramer composed of identical subunits, so self-association is a bona fide, functionally meaningful property (the active enzyme is the tetramer). Multiple independent interactome studies report the self-interaction. Supporting Evidence: PMID:8792870 Argininosuccinate synthetase (ASS) is a urea cycle enzyme with a tetrameric
GO:0042802 identical protein binding	IPI PMID:21988832 Toward an understanding of the protein interaction network o...	ACCEPT	Summary: Self-interaction detected in a human liver protein-interaction network study, consistent with the homotetrameric architecture of ASS1. Reason: Corroborates the homotetramer; "identical protein binding" is a meaningful function for this obligate oligomer. Supporting Evidence: PMID:8792870 Argininosuccinate synthetase (ASS) is a urea cycle enzyme with a tetrameric
GO:0042802 identical protein binding	IPI PMID:25416956 A proteome-scale map of the human interactome network.	ACCEPT	Summary: Self-interaction from a proteome-scale human interactome map, again consistent with the homotetramer. Reason: Reinforces the biologically meaningful homo-oligomerization of ASS1. Supporting Evidence: PMID:8792870 Argininosuccinate synthetase (ASS) is a urea cycle enzyme with a tetrameric
GO:0000050 urea cycle	IEA GO_REF:0000120	ACCEPT	Summary: Automated urea cycle assignment, matching UniPathway UPA00158. Reason: Correct core process, redundant with IBA and multiple experimental IMP annotations.
GO:0001822 kidney development	IEA GO_REF:0000107	KEEP AS NON CORE	Summary: Ensembl-Compara ortholog-transfer from rat. ASS1 is expressed in fetal kidney and is part of the intestinal-renal citrulline-arginine axis, but a direct role in kidney developmental morphogenesis is not established for the human enzyme; this reads as an expression/context annotation rather than a developmental function. Reason: Ortholog-transfer IEA reflecting a tissue in which ASS1 is expressed and active rather than a core molecular role in organ development. Not a core function; retain as non-core pending direct evidence.
GO:0001889 liver development	IEA GO_REF:0000107	KEEP AS NON CORE	Summary: Ensembl-Compara ortholog-transfer from rat. ASS1 is the principal hepatic urea-cycle enzyme and is developmentally regulated in fetal liver, but "liver development" (organ morphogenesis) overstates its role; its liver function is metabolic (ureagenesis). Reason: Ortholog-transfer IEA describing the tissue context (liver) of ASS1 expression rather than a causal role in liver organogenesis. Retain as non-core; the metabolic role is captured by the urea cycle / arginine biosynthesis annotations.
GO:0005739 mitochondrion	IEA GO_REF:0000107	REMOVE	Summary: Ensembl-Compara ortholog-transfer (from mouse) placing ASS1 in the mitochondrion. This contradicts the well-established cytosolic localization of ASS1; the enzyme acts in the cytosol on citrulline exported from mitochondria. Reason: ASS1 is a soluble cytosolic enzyme (UniProt: Cytoplasm, cytosol; direct IDA cytosol annotations). Mitochondrial localization is an over-propagated ortholog-transfer IEA inconsistent with the human protein and with urea-cycle compartmentalization (only the upstream steps CPS1/OTC are mitochondrial).
GO:0005741 mitochondrial outer membrane	IEA GO_REF:0000107	REMOVE	Summary: Ensembl-Compara ortholog-transfer (from rat) placing ASS1 at the mitochondrial outer membrane. Inconsistent with the established cytosolic localization of the enzyme. Reason: Over-propagated ortholog-transfer IEA. ASS1 is cytosolic; there is no reliable evidence for the human enzyme residing at the mitochondrial outer membrane.
GO:0006953 acute-phase response	IEA GO_REF:0000107	KEEP AS NON CORE	Summary: Ensembl-Compara ortholog-transfer from rat. Reflects transcriptional induction of ASS1 under inflammatory/cytokine stimulation rather than a direct molecular role in the acute-phase response. Reason: Regulation-of-expression / stimulus-response context transferred from ortholog, not a core catalytic role. Retain as non-core.
GO:0007494 midgut development	IEA GO_REF:0000107	KEEP AS NON CORE	Summary: Ensembl-Compara ortholog-transfer from rat. Likely reflects intestinal ASS1 expression (enterocytes contribute to systemic citrulline/arginine metabolism) rather than a role in gut morphogenesis. Reason: Ortholog-transfer IEA describing an expression context, not a core developmental function of the human enzyme. Retain as non-core.
GO:0007584 response to nutrient	IEA GO_REF:0000107	KEEP AS NON CORE	Summary: Ensembl-Compara ortholog-transfer from rat. ASS1 expression/activity responds to dietary protein and amino acid availability, but this is a stimulus-response context, not a core molecular function. Reason: Physiologically plausible (urea-cycle flux tracks nitrogen load) but an ortholog-transfer response annotation rather than core function. Retain as non-core.
GO:0007623 circadian rhythm	IEA GO_REF:0000107	KEEP AS NON CORE	Summary: Ensembl-Compara ortholog-transfer from mouse. This is corroborated by direct human/mouse evidence: CLOCK acetylates ASS1 (K165/K176) to inactivate it in a circadian manner, imposing a circadian rhythm on ureagenesis. Reason: Supported by experiment (see the IDA circadian rhythm annotation, PMID:28985504), but this is a regulated-behavior/output context rather than ASS1's core catalytic function. Retain as non-core; redundant with the experimental annotation below. Supporting Evidence: PMID:28985504 ASS1 acetylation by CLOCK exhibits circadian oscillation
GO:0009410 response to xenobiotic stimulus	IEA GO_REF:0000107	KEEP AS NON CORE	Summary: Ensembl-Compara ortholog-transfer from rat, reflecting altered ASS1 expression on xenobiotic exposure. Stimulus-response context, not a core function. Reason: Ortholog-transfer response annotation; retain as non-core.
GO:0009636 response to toxic substance	IEA GO_REF:0000107	KEEP AS NON CORE	Summary: Ensembl-Compara ortholog-transfer from rat. A broad stimulus-response term reflecting expression changes; not a core molecular function. Reason: Ortholog-transfer response annotation with no direct human evidence for a core role; retain as non-core.
GO:0010043 response to zinc ion	IEA GO_REF:0000107	KEEP AS NON CORE	Summary: Ensembl-Compara ortholog-transfer from rat; a specific stimulus-response context. Reason: Ortholog-transfer response annotation, not core function; retain as non-core.
GO:0010046 response to mycotoxin	IEA GO_REF:0000107	KEEP AS NON CORE	Summary: Ensembl-Compara ortholog-transfer from rat; narrow stimulus-response context. Reason: Ortholog-transfer response annotation, not core function; retain as non-core.
GO:0014075 response to amine	IEA GO_REF:0000107	KEEP AS NON CORE	Summary: Ensembl-Compara ortholog-transfer from rat; stimulus-response context. Reason: Ortholog-transfer response annotation, not core function; retain as non-core.
GO:0015643 toxic substance binding	IEA GO_REF:0000107	REMOVE	Summary: Ensembl-Compara ortholog-transfer from rat asserting ASS1 "binds a toxic substance". There is no credible biochemical basis for treating ASS1 as a toxin-binding protein; ASS1 is a metabolic ligase. This is an anomalous, likely spuriously propagated molecular-function IEA. Reason: Biologically implausible for a cytosolic urea-cycle ligase; unsupported by any human evidence or by the enzyme's mechanism. The term definition ("Binding to a toxic substance, a poisonous substance that causes damage to biological systems") does not fit ASS1. Over-propagated ortholog-transfer IEA.
GO:0032355 response to estradiol	IEA GO_REF:0000107	KEEP AS NON CORE	Summary: Ensembl-Compara ortholog-transfer from rat; hormone stimulus-response context. Reason: Ortholog-transfer response annotation, not core function; retain as non-core.
GO:0032496 response to lipopolysaccharide	IEA GO_REF:0000107	KEEP AS NON CORE	Summary: Ensembl-Compara ortholog-transfer from rat. ASS1 is induced with iNOS in inflammatory (LPS/cytokine) settings to supply arginine for NO production, so this context is plausible, but it is not a core function. Reason: Ortholog-transfer response annotation consistent with the citrulline-NO cycle role in immune/inflammatory cells; retain as non-core.
GO:0043025 neuronal cell body	IEA GO_REF:0000107	KEEP AS NON CORE	Summary: Ensembl-Compara ortholog-transfer from rat placing ASS1 in the neuronal cell body. ASS1 is expressed in specific neurons (citrulline-NO cycle), and within a neuron it would be cytosolic; the specific location is an ortholog-transferred expression context. Reason: Cell-type-specific localization transferred from ortholog; plausible for the tissue context but not the canonical/core cytosolic annotation. Retain as non-core.
GO:0043200 response to amino acid	IEA GO_REF:0000107	KEEP AS NON CORE	Summary: Ensembl-Compara ortholog-transfer from rat; amino-acid stimulus-response context (ASS1 expression/activity responds to substrate and amino acid availability). Reason: Ortholog-transfer response annotation, not core function; retain as non-core.
GO:0043204 perikaryon	IEA GO_REF:0000107	KEEP AS NON CORE	Summary: Ensembl-Compara ortholog-transfer from rat placing ASS1 in the perikaryon (neuronal cell body cytoplasm). A cell-type-specific location transferred from ortholog. Reason: Ortholog-transfer localization tied to a specific tissue context; not the canonical/core cytosol annotation. Retain as non-core.
GO:0043434 response to peptide hormone	IEA GO_REF:0000107	KEEP AS NON CORE	Summary: Ensembl-Compara ortholog-transfer from rat; hormone stimulus-response context. Reason: Ortholog-transfer response annotation, not core function; retain as non-core.
GO:0048545 response to steroid hormone	IEA GO_REF:0000107	KEEP AS NON CORE	Summary: Ensembl-Compara ortholog-transfer from rat; steroid-hormone stimulus-response context (ASS1 is known to be glucocorticoid-inducible). Reason: Ortholog-transfer response annotation, not core function; retain as non-core.
GO:0051384 response to glucocorticoid	IEA GO_REF:0000107	KEEP AS NON CORE	Summary: Ensembl-Compara ortholog-transfer from rat. ASS1 transcription is induced by glucocorticoids (hepatic urea-cycle regulation), so this context is plausible. Reason: Ortholog-transfer response annotation reflecting hormonal regulation of expression, not core catalytic function; retain as non-core.
GO:0060416 response to growth hormone	IEA GO_REF:0000107	KEEP AS NON CORE	Summary: Ensembl-Compara ortholog-transfer from rat; hormone stimulus-response context. Reason: Ortholog-transfer response annotation, not core function; retain as non-core.
GO:0060539 diaphragm development	IEA GO_REF:0000107	KEEP AS NON CORE	Summary: Ensembl-Compara ortholog-transfer from rat. There is no established human evidence linking ASS1 to diaphragm morphogenesis; this reads as a weakly supported ortholog-transferred developmental annotation. Reason: Ortholog-transfer developmental annotation lacking direct human support; not a core function. Retain as non-core rather than removing, deferring to the experimental source in the orthologous species.
GO:0070542 response to fatty acid	IEA GO_REF:0000107	KEEP AS NON CORE	Summary: Ensembl-Compara ortholog-transfer from rat; stimulus-response context. Reason: Ortholog-transfer response annotation, not core function; retain as non-core.
GO:0070852 cell body fiber	IEA GO_REF:0000107	KEEP AS NON CORE	Summary: Ensembl-Compara ortholog-transfer from rat; a neuronal cell-type-specific location. Reason: Ortholog-transfer localization for a specific tissue context; not the canonical/core cytosol annotation. Retain as non-core.
GO:0071222 cellular response to lipopolysaccharide	IEA GO_REF:0000107	KEEP AS NON CORE	Summary: Ensembl-Compara ortholog-transfer from rat; cellular stimulus-response context (inflammatory induction of ASS1 for arginine/NO supply). Reason: Ortholog-transfer response annotation consistent with the citrulline-NO cycle in immune cells; retain as non-core.
GO:0071230 cellular response to amino acid stimulus	IEA GO_REF:0000107	KEEP AS NON CORE	Summary: Ensembl-Compara ortholog-transfer from rat; amino-acid stimulus-response context. Reason: Ortholog-transfer response annotation, not core function; retain as non-core.
GO:0071242 cellular response to ammonium ion	IEA GO_REF:0000107	KEEP AS NON CORE	Summary: Ensembl-Compara ortholog-transfer from rat; stimulus-response context (ureagenesis responds to nitrogen/ammonia load). Reason: Ortholog-transfer response annotation, not core function; retain as non-core.
GO:0071320 cellular response to cAMP	IEA GO_REF:0000107	KEEP AS NON CORE	Summary: Ensembl-Compara ortholog-transfer from rat; second-messenger stimulus-response context. Reason: Ortholog-transfer response annotation, not core function; retain as non-core.
GO:0071346 cellular response to type II interferon	IEA GO_REF:0000107	KEEP AS NON CORE	Summary: Ensembl-Compara ortholog-transfer from rat; cytokine (IFN-gamma) stimulus-response context, consistent with immune induction of ASS1 for arginine/NO supply. Reason: Ortholog-transfer response annotation, not core function; retain as non-core.
GO:0071356 cellular response to tumor necrosis factor	IEA GO_REF:0000107	KEEP AS NON CORE	Summary: Ensembl-Compara ortholog-transfer from rat; cytokine (TNF) stimulus-response context. Related human work shows ASS1/NOS3 counteract TNF-alpha-stimulated monocyte adhesion in endothelium. Reason: Ortholog-transfer response annotation, not core function; retain as non-core.
GO:0071377 cellular response to glucagon stimulus	IEA GO_REF:0000107	KEEP AS NON CORE	Summary: Ensembl-Compara ortholog-transfer from rat; hormone stimulus-response context (glucagon induces hepatic urea-cycle enzymes). Reason: Ortholog-transfer response annotation, not core function; retain as non-core.
GO:0071400 cellular response to oleic acid	IEA GO_REF:0000107	KEEP AS NON CORE	Summary: Ensembl-Compara ortholog-transfer from rat; a narrow fatty-acid stimulus-response context. Reason: Ortholog-transfer response annotation, not core function; retain as non-core.
GO:0071418 cellular response to amine stimulus	IEA GO_REF:0000107	KEEP AS NON CORE	Summary: Ensembl-Compara ortholog-transfer from rat; amine stimulus-response context. Reason: Ortholog-transfer response annotation, not core function; retain as non-core.
GO:0071549 cellular response to dexamethasone stimulus	IEA GO_REF:0000107	KEEP AS NON CORE	Summary: Ensembl-Compara ortholog-transfer from rat; glucocorticoid (dexamethasone) stimulus-response context, consistent with glucocorticoid induction of ASS1. Reason: Ortholog-transfer response annotation, not core function; retain as non-core.
GO:0000050 urea cycle	IMP PMID:7977368 Mutations in argininosuccinate synthetase mRNA of Japanese p...	ACCEPT	Summary: Experimental (IMP) urea cycle annotation based on characterization of citrullinemia-causing ASS1 mutations in patients. Loss of ASS1 function blocks the urea cycle, causing classic citrullinemia. Reason: Directly supported by patient mutation genetics; a core biological process. Defer to the curator's full-text reading of the disease-gene relationship. Supporting Evidence: PMID:7977368 Citrullinemia is an autosomal recessive disease caused by a genetic deficiency
GO:0006533 L-aspartate catabolic process	IMP PMID:7977368 Mutations in argininosuccinate synthetase mRNA of Japanese p...	KEEP AS NON CORE	Summary: Experimental (IMP) annotation reflecting that ASS1 consumes L-aspartate (the second nitrogen donor) in the argininosuccinate synthase reaction. This is a curator reframing of the same catalytic step as an aspartate catabolic process. Reason: Not incorrect (ASS1 does consume aspartate as a co-substrate), but it is a redundant, substrate-centric restatement of the core argininosuccinate synthase activity / urea cycle role rather than an independent biological process. Retain as non-core; defer to the experimental curator who read the full text. Supporting Evidence: PMID:7977368 Citrullinemia is an autosomal recessive disease caused by a genetic deficiency
GO:0019241 L-citrulline catabolic process	IMP PMID:7977368 Mutations in argininosuccinate synthetase mRNA of Japanese p...	KEEP AS NON CORE	Summary: Experimental (IMP) annotation reflecting that ASS1 consumes L-citrulline in the argininosuccinate synthase reaction; ASS1 deficiency causes citrulline accumulation. This is a substrate-centric reframing of the same catalytic step. Reason: Not incorrect (citrulline is the substrate whose accumulation defines citrullinemia), but it is a redundant restatement of the core enzyme activity / arginine-biosynthesis and urea-cycle roles. Retain as non-core; defer to the experimental curator. Supporting Evidence: PMID:7977368 Citrullinemia is an autosomal recessive disease caused by a genetic deficiency
GO:0005829 cytosol	IDA GO_REF:0000052	ACCEPT	Summary: Direct immunofluorescence (Human Protein Atlas) localization to the cytosol. Reason: Experimental confirmation of the core cytosolic localization of ASS1.
GO:0005829 cytosol	TAS Reactome:R-HSA-9956517	ACCEPT	Summary: Reactome traceable-author-statement placing ASS1 (in the context of disease variants failing to synthesize argininosuccinate) in the cytosol. Reason: Consistent with the established cytosolic localization; redundant but correct.
GO:0004055 argininosuccinate synthase activity	IMP PMID:28985504 CLOCK Acetylates ASS1 to Drive Circadian Rhythm of Ureagenes...	ACCEPT	Summary: Experimental (IMP) support for ASS1 catalytic activity from the CLOCK-acetylation study, which manipulated ASS1 and measured its activity (acetylation of K165/K176 inactivates the enzyme). Reason: Core molecular function directly assayed in the study; ASS1 "catalyzes the rate-limiting step of arginine biosynthesis". Supporting Evidence: PMID:28985504 synthase (ASS1) to inactivate ASS1, which catalyzes the rate-limiting step of
GO:0005515 protein binding	IPI PMID:28985504 CLOCK Acetylates ASS1 to Drive Circadian Rhythm of Ureagenes...	REMOVE	Summary: IntAct/UniProt interaction with CLOCK (O15516) demonstrated in the circadian-ureagenesis study. Captured only as uninformative "protein binding". Reason: Bare "protein binding" is discouraged. The ASS1-CLOCK interaction is genuine and functionally important (CLOCK acetylates ASS1), but this content is retained in the description and in the circadian-rhythm annotation; the uninformative GO:0005515 term itself adds nothing. Supporting Evidence: PMID:28985504 CLOCK directly acetylates K165 and K176 of argininosuccinate
GO:0005829 cytosol	IDA PMID:28985504 CLOCK Acetylates ASS1 to Drive Circadian Rhythm of Ureagenes...	ACCEPT	Summary: Direct experimental (IDA) cytosolic localization from the CLOCK-acetylation study; UniProt cites this paper for the Cytoplasm, cytosol subcellular location. Reason: Experimental confirmation of the core cytosolic localization.
GO:0007623 circadian rhythm	IDA PMID:28985504 CLOCK Acetylates ASS1 to Drive Circadian Rhythm of Ureagenes...	KEEP AS NON CORE	Summary: Direct experimental (IDA) evidence that ASS1 activity is under circadian control: CLOCK acetylates ASS1 in a circadian manner, producing an oscillation in ASS1 activity and ureagenesis in human cells and mouse liver. Reason: Well supported experimentally, but this describes a regulated output/behavior in which ASS1 participates rather than ASS1's intrinsic core function. Retain as non-core. Supporting Evidence: PMID:28985504 ASS1 acetylation by CLOCK exhibits circadian oscillation
GO:0000050 urea cycle	IMP PMID:8792870 Characterization of human wild-type and mutant argininosucci...	ACCEPT	Summary: Experimental (IMP) urea cycle annotation from characterization of wild-type and mutant human ASS proteins; the paper explicitly frames ASS as a urea cycle enzyme and links mutations to citrullinemia. Reason: Core biological process, directly supported by recombinant enzymology of the human protein. Supporting Evidence: PMID:8792870 Argininosuccinate synthetase (ASS) is a urea cycle enzyme with a tetrameric
GO:0004055 argininosuccinate synthase activity	IMP PMID:8792870 Characterization of human wild-type and mutant argininosucci...	ACCEPT	Summary: Experimental (IMP) measurement of ASS catalytic activity: purified recombinant wild-type human ASS matched native liver enzyme, and mutants showed reduced/abolished activity and abnormal kinetics (elevated Km for citrulline). Reason: Direct biochemical characterization of the core molecular function of the human enzyme. Supporting Evidence: PMID:8792870 G280R mutant was extracted with an amount of ASS protein similar to wild-type
GO:0006526 L-arginine biosynthetic process	IMP PMID:8792870 Characterization of human wild-type and mutant argininosucci...	ACCEPT	Summary: Experimental (IMP) support for ASS1's role in arginine biosynthesis via the biochemical characterization of the enzyme that carries out the committed step. Reason: Core biological process supported by the human enzymology; defer to the experimental curator. Supporting Evidence: PMID:8792870 Argininosuccinate synthetase (ASS) is a urea cycle enzyme with a tetrameric
GO:0000050 urea cycle	IMP PMID:18473344 Investigation of citrullinemia type I variants by in vitro e...	ACCEPT	Summary: Experimental (IMP) urea cycle annotation from in vitro expression/enzymology of CTLN1 variants; the paper describes ASS as "the urea cycle enzyme argininosuccinate synthetase". Reason: Core biological process supported by disease-variant enzymology. Supporting Evidence: PMID:18473344 caused by deficiency of the urea cycle enzyme argininosuccinate synthetase
GO:0004055 argininosuccinate synthase activity	IMP PMID:18473344 Investigation of citrullinemia type I variants by in vitro e...	ACCEPT	Summary: Experimental (IMP) enzymatic analysis of purified wild-type and mutant ASS proteins, with measured kinetic parameters (KM 112 uM citrulline, 68 uM aspartate) and reduced activity for pathogenic variants. Reason: Direct measurement of the core catalytic activity; underpins the UniProt EC 6.3.4.5 and kinetic parameters. Supporting Evidence: PMID:18473344 enzymatic analysis of purified wild-type and the mutant ASS proteins
GO:0006526 L-arginine biosynthetic process	IMP PMID:18473344 Investigation of citrullinemia type I variants by in vitro e...	ACCEPT	Summary: Experimental (IMP) support for the arginine-biosynthesis role via enzymology of the ASS reaction, which produces argininosuccinate en route to arginine. Reason: Core biological process supported by the human enzyme characterization. Supporting Evidence: PMID:18473344 caused by deficiency of the urea cycle enzyme argininosuccinate synthetase
GO:0000050 urea cycle	IMP PMID:27287393 Kinetic mutations in argininosuccinate synthetase deficiency...	ACCEPT	Summary: Experimental (IMP) urea cycle annotation from characterization of 21 kinetic CTLN1 mutations; the paper frames citrullinemia type 1 as "an autosomal-recessive urea cycle disorder". Reason: Core biological process supported by disease-mutation enzymology. Supporting Evidence: PMID:27287393 BACKGROUND: Citrullinemia type 1 is an autosomal-recessive urea cycle disorder
GO:0004055 argininosuccinate synthase activity	IMP PMID:27287393 Kinetic mutations in argininosuccinate synthetase deficiency...	ACCEPT	Summary: Experimental (IMP) measurement of ASS catalytic activity and kinetics for 21 mutants by tandem mass spectrometry; 13 were inactive and 8 had decreased substrate affinity, rescuable by aspartate supplementation. Reason: Direct quantitative measurement of the core molecular function of the human enzyme. Supporting Evidence: PMID:27287393 activity and kinetic parameters were measured using tandem mass spectrometry and
GO:0006526 L-arginine biosynthetic process	IMP PMID:27287393 Kinetic mutations in argininosuccinate synthetase deficiency...	ACCEPT	Summary: Experimental (IMP) support for the arginine-biosynthesis role via kinetic characterization of the ASS reaction (citrulline + aspartate + ATP -> argininosuccinate). Reason: Core biological process supported by the human enzyme kinetics. Supporting Evidence: PMID:27287393 map near the substrate (aspartate or citrulline)
GO:0070062 extracellular exosome	HDA PMID:23533145 In-depth proteomic analyses of exosomes isolated from expres...	KEEP AS NON CORE	Summary: High-throughput detection of ASS1 peptides in urinary/prostatic exosome proteomes. This is a mass-spectrometry proteomic inventory, not evidence of a functional extracellular-vesicle localization for a cytosolic metabolic enzyme. Reason: Abundant cytosolic enzymes are common background hits in exosome/secretome proteomics; the finding is real as a detection event but does not reflect a core functional localization. Retain as non-core rather than removing, since the peptide detection is genuine. Supporting Evidence: PMID:23533145 expressed prostatic secretions in urine (EPS-urine), exosome preparations were
GO:0004055 argininosuccinate synthase activity	IMP PMID:7977368 Mutations in argininosuccinate synthetase mRNA of Japanese p...	ACCEPT	Summary: Experimental (IMP) support for the catalytic activity via mutation analysis in citrullinemia patients; the deficiency of ASS activity underlies the disease. Reason: Core molecular function supported by patient genetics; defer to the experimental curator. Supporting Evidence: PMID:7977368 Citrullinemia is an autosomal recessive disease caused by a genetic deficiency
GO:0016597 amino acid binding	IMP PMID:7977368 Mutations in argininosuccinate synthetase mRNA of Japanese p...	ACCEPT	Summary: Experimental (IMP) annotation of amino acid binding, reflecting that ASS1 binds its amino acid substrates L-citrulline and L-aspartate; several CTLN1 mutations map to the substrate (aspartate/citrulline) binding site and impair substrate affinity. Reason: Informative molecular function distinct from the catalytic term: ASS1 has bona fide amino acid (citrulline/aspartate) binding sites (documented in UniProt BINDING features), and kinetic mutants show altered Km. Supported by the experimental mutation studies. Supporting Evidence: PMID:27287393 map near the substrate (aspartate or citrulline)
GO:0045429 positive regulation of nitric oxide biosynthetic process	IMP PMID:21106532 Endothelial argininosuccinate synthetase 1 regulates nitric ...	KEEP AS NON CORE	Summary: Experimental (IMP) evidence in endothelial cells that ASS1, by regenerating arginine (the NOS3 substrate) from citrulline, increases NO production; overexpression of ASS1 raised NO and ASS1/NOS3 siRNAs attenuated shear-stress-induced NO. This is the citrulline-NO cycle role. Reason: Genuine, physiologically important extrahepatic function of ASS1 (supplying arginine for NO synthesis) but it is a downstream regulatory consequence of the core arginine-biosynthesis activity in a specific cell type, not the enzyme's intrinsic core function. Retain as non-core. Supporting Evidence: PMID:21106532 increased NO production and decreased monocyte adhesion stimulated by tumor
GO:0071499 cellular response to laminar fluid shear stress	IMP PMID:21106532 Endothelial argininosuccinate synthetase 1 regulates nitric ...	KEEP AS NON CORE	Summary: Experimental (IMP) evidence that laminar shear stress induces ASS1 in endothelial cells and that ASS1 (with NOS3) is required for the shear-stress-stimulated increase in NO production. Reason: A cell-type-specific stimulus-response/physiological role, downstream of ASS1's core arginine supply function; not the enzyme's intrinsic core function. Retain as non-core. Supporting Evidence: PMID:21106532 SiRNAs of NOS3 and ASS1 attenuated
GO:1903038 negative regulation of leukocyte cell-cell adhesion	IMP PMID:21106532 Endothelial argininosuccinate synthetase 1 regulates nitric ...	KEEP AS NON CORE	Summary: Experimental (IMP) evidence that ASS1 (via NO production) reduces TNF-alpha-stimulated monocyte adhesion to endothelial cells, an anti-inflammatory endothelial effect downstream of arginine/NO supply. Reason: A downstream physiological consequence of the endothelial citrulline-NO cycle role, mediated by NO rather than a direct ASS1 activity on adhesion; not a core function. Retain as non-core. Supporting Evidence: PMID:21106532 increased NO production and decreased monocyte adhesion stimulated by tumor
GO:0003723 RNA binding	HDA PMID:22658674 Insights into RNA biology from an atlas of mammalian mRNA-bi...	MARK AS OVER ANNOTATED	Summary: High-throughput "interactome capture" detection of ASS1 among mRNA-binding proteins in proliferating HeLa cells (mRNA interactome atlas). Many metabolic enzymes were unexpectedly captured; no dedicated RNA-binding function has been demonstrated for ASS1. Reason: This derives from a single high-throughput RNA-interactome screen that recovered numerous "moonlighting" metabolic enzymes. There is no orthogonal validation of a functional RNA-binding role for ASS1, so it is very likely an over-annotation rather than a core or established secondary function. Flag as over-annotated rather than accepting. Supporting Evidence: PMID:22658674 RNA-binding enzymes of intermediary
GO:0070062 extracellular exosome	HDA PMID:19056867 Large-scale proteomics and phosphoproteomics of urinary exos...	KEEP AS NON CORE	Summary: High-throughput detection of ASS1 in a large-scale urinary-exosome proteome. As above, an MS inventory hit for a cytosolic enzyme rather than evidence of a functional extracellular localization. Reason: Genuine peptide detection in an exosome proteomics dataset, but not a core functional localization for this cytosolic urea-cycle enzyme. Retain as non-core. Supporting Evidence: PMID:19056867 Normal human urine contains large numbers of exosomes
GO:0005829 cytosol	TAS Reactome:R-HSA-70577	ACCEPT	Summary: Reactome traceable-author-statement localizing the ASS1 tetramer (in complex with NMRAL1 dimer and NADPH) to the cytosol, in the argininosuccinate-forming reaction. Reason: Consistent with the established cytosolic localization of ASS1; correct.
GO:0005737 cytoplasm	TAS PMID:6194510 Sequence for human argininosuccinate synthetase cDNA.	MODIFY	Summary: Traceable author statement (from the human ASS cDNA sequencing paper) localizing ASS1 to the cytoplasm. This is the general parent of the more specific cytosol annotations. Reason: Correct but less specific than warranted: ASS1 is specifically cytosolic (GO:0005829), which is directly supported by immunofluorescence (IDA) and multiple sources. Replace the general "cytoplasm" with the more informative "cytosol". Proposed replacements: cytosol

Core Functions

Argininosuccinate synthase: ATP-dependent condensation of L-citrulline and L-aspartate to form argininosuccinate (plus AMP and diphosphate) in the cytosol. This is the rate-limiting, committed step of de novo L-arginine biosynthesis and the argininosuccinate-forming step of the urea cycle, in which aspartate is the second nitrogen donor. The enzyme functions as a homotetramer of identical subunits, uses ATP as co-substrate (with defined ATP- and amino acid-binding sites), and its product is handed to argininosuccinate lyase (ASL) to yield arginine and fumarate.

Molecular Function:

argininosuccinate synthase activity

Directly Involved In:

urea cycle L-arginine biosynthetic process

Cellular Locations:

cytosol

Substrates:

L-citrulline L-aspartate ATP

Supporting Evidence:

PMID:8792870
Argininosuccinate synthetase (ASS) is a urea cycle enzyme with a tetrameric
PMID:27287393
map near the substrate (aspartate or citrulline)
PMID:28985504
synthase (ASS1) to inactivate ASS1, which catalyzes the rate-limiting step of

References

GO_REF:0000002

Gene Ontology annotation through association of InterPro records with GO terms

GO_REF:0000033

Annotation inferences using phylogenetic trees

GO_REF:0000044

Gene Ontology annotation based on UniProtKB/Swiss-Prot Subcellular Location vocabulary mapping, accompanied by conservative changes to GO terms applied by UniProt

GO_REF:0000052

Gene Ontology annotation based on curation of immunofluorescence data

GO_REF:0000107

Automatic transfer of experimentally verified manual GO annotation data to orthologs using Ensembl Compara

GO_REF:0000120

Combined Automated Annotation using Multiple IEA Methods

PMID:12620389

Novel raf kinase protein-protein interactions found by an exhaustive yeast two-hybrid analysis.

PMID:16189514

Towards a proteome-scale map of the human protein-protein interaction network.

PMID:17496144

Restructuring of the dinucleotide-binding fold in an NADP(H) sensor protein.

PMID:18473344

Investigation of citrullinemia type I variants by in vitro expression studies.

PMID:19056867

Large-scale proteomics and phosphoproteomics of urinary exosomes.

PMID:21106532

Endothelial argininosuccinate synthetase 1 regulates nitric oxide production and monocyte adhesion under static and laminar shear stress conditions.

PMID:21988832

Toward an understanding of the protein interaction network of the human liver.

PMID:22658674

Insights into RNA biology from an atlas of mammalian mRNA-binding proteins.

PMID:23533145

In-depth proteomic analyses of exosomes isolated from expressed prostatic secretions in urine.

PMID:25416956

A proteome-scale map of the human interactome network.

PMID:27287393

Kinetic mutations in argininosuccinate synthetase deficiency: characterisation and in vitro correction by substrate supplementation.

PMID:28587924

PRMT7 Interacts with ASS1 and Citrullinemia Mutations Disrupt the Interaction.

PMID:28985504

CLOCK Acetylates ASS1 to Drive Circadian Rhythm of Ureagenesis.

PMID:6194510

Sequence for human argininosuccinate synthetase cDNA.

PMID:7977368

Mutations in argininosuccinate synthetase mRNA of Japanese patients, causing classical citrullinemia.

PMID:8792870

Characterization of human wild-type and mutant argininosuccinate synthetase proteins expressed in bacterial cells.

Reactome:R-HSA-70577

ASS1 tetramer:NMRAL1 dimer:NADPH transforms L-Asp and L-Cit to ARSUA

Reactome:R-HSA-9956517

ASS1 variants don't synthesize arginosuccinate

Deep Research

Falcon

(ASS1-deep-research-falcon.md)

Comprehensive Research Report: Human ASS1 (Argininosuccinate Synthase 1) Falcon Edison Scientific Literature 32 citations 2 artifacts 2026-07-05T13:33:02.628505

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Edison artifact artifact-01 (text/markdown)

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Comprehensive Research Report: Human ASS1 (Argininosuccinate Synthase 1)

1. Gene and Protein Identity

ASS1 (also known as ASS; HGNC:758) encodes argininosuccinate synthase 1 (UniProt: P00966), a 412-residue (~46 kDa) cytosolic enzyme classified under EC 6.3.4.5 (diezfernandez2017mutationsinthe pages 1-6, karlberg2008structureofhuman pages 1-2). The protein belongs to the argininosuccinate synthase family, type 1 subfamily, and is one of the most extensively studied urea cycle enzymes in humans.

The following table summarizes the key properties of ASS1:

Property	Summary
Gene name	ASS1; synonym: ASS (human argininosuccinate synthase 1) (karlberg2008structureofhuman pages 1-2, diezfernandez2017mutationsinthe pages 1-6)
Protein name	Argininosuccinate synthase 1; catalyzes argininosuccinate formation in arginine biosynthesis/urea cycle (karlberg2008structureofhuman pages 1-2, fung2025arginineatthe pages 2-3)
UniProt ID	P00966
EC number	EC 6.3.4.5 (argininosuccinate synthase) (karlberg2008structureofhuman pages 1-2)
Organism	Homo sapiens (Human)
Molecular weight	Monomer is approximately 46 kDa (diezfernandez2017mutationsinthe pages 1-6)
Oligomeric state	Homotetramer; tetrameric state is conserved and required for activity (diezfernandez2017mutationsinthe pages 1-6, karlberg2008structureofhuman pages 3-5)
Subcellular localization	Primarily cytosolic; in liver associated with periportal hepatocyte urea-cycle function; can accumulate in the nucleus during DNA damage responses; reported association with caveolae in endothelial cells (lim2024ass1metabolicallycontributes pages 6-6, finnie2020investigatingass1and pages 100-105)
Primary substrates	Citrulline, L-aspartate, and ATP (karlberg2008structureofhuman pages 1-2, karlberg2008structureofhuman pages 5-6)
Primary products	Argininosuccinate, AMP, and pyrophosphate (PPi) (karlberg2008structureofhuman pages 1-2)
Catalyzed reaction	ATP-dependent condensation of citrulline with aspartate to form argininosuccinate; rate-limiting step of de novo arginine synthesis and a key urea-cycle step (karlberg2008structureofhuman pages 1-2, delage2010argininedeprivationand pages 2-3)
Key active-site residues	Residues implicated in substrate binding/catalysis include Glu270, Tyr282, Arg127, Asn123, Tyr87, Ser189, Thr119, Gln40; Arg127 and Asn123 help bind substrates, and domain movement helps position citrulline for attack on ATP (karlberg2008structureofhuman pages 5-6, karlberg2008structureofhuman pages 6-7)
Domain architecture	Three-part architecture: nucleotide-binding domain, synthetase domain, and C-terminal oligomerization helix (diezfernandez2017mutationsinthe pages 1-6, karlberg2008structureofhuman pages 3-5)
Key regulatory modifications	CLOCK-mediated acetylation at K165/K176 rhythmically inhibits ASS1 activity and drives circadian ureagenesis; Cys132 nitrosylation has been reported as an inactivating mammalian regulatory modification (lin2017clockacetylatesass1 pages 8-9, lin2017clockacetylatesass1 pages 3-4, lin2017clockacetylatesass1 pages 6-7, karlberg2008structureofhuman pages 5-6)
Major pathway roles	Functions in the urea cycle, de novo arginine biosynthesis, and citrulline–NO cycle; also influences nucleotide synthesis by competing for aspartate and can link ureagenesis to hepatic AMPK/lipid metabolism (fung2025arginineatthe pages 2-3, delage2010argininedeprivationand pages 2-3, sun2022argininosuccinatesynthase1 pages 2-4, madiraju2016argininosuccinatesynthetaseregulates pages 5-5)
Recent non-canonical functions	In 2024, ASS1 was shown to have a nuclear DNA-damage-response role: after DNA damage it accumulates in the nucleus, generates fumarate with ASL, promotes SMARCC1 succination, and modulates p53-regulated chromatin accessibility/transcription (lim2024ass1metabolicallycontributes pages 6-6, lim2024ass1metabolicallycontributes pages 4-5)
Associated diseases/contexts	Citrullinemia type I (CTLN1) from biallelic ASS1 deficiency causes hyperammonemia and elevated citrulline; in cancer, ASS1 silencing creates arginine auxotrophy and therapeutic vulnerability to arginine deprivation (diezfernandez2017mutationsinthe pages 10-14, diezfernandez2017mutationsinthe pages 14-18, ribas2022hyperammonemiaininherited pages 4-5, rogers2022canonicalandnoncanonical pages 13-17, delage2010argininedeprivationand pages 3-5)
PDB structure ID	2NZ2 (human ASS1 crystal structure) (diezfernandez2017mutationsinthe pages 22-27)
Protein family	Argininosuccinate synthase family, type 1 subfamily; structurally conserved tetrameric enzyme family (diezfernandez2017mutationsinthe pages 1-6, karlberg2008structureofhuman pages 3-5)

Table: This table summarizes the core biochemical, structural, localization, regulatory, and disease-associated properties of human ASS1. It is useful as a compact reference for functional annotation and interpretation of recent ASS1 literature.

2. Enzymatic Function: Reaction, Substrates, and Mechanism

2.1 Catalyzed Reaction

ASS1 catalyzes the ATP-dependent condensation of L-citrulline and L-aspartate to form argininosuccinate, with concomitant production of AMP and pyrophosphate (PPi) (karlberg2008structureofhuman pages 1-2). This reaction constitutes the rate-limiting step in both the urea cycle and de novo arginine biosynthesis (delage2010argininedeprivationand pages 2-3). The overall reaction is:

L-Citrulline + L-Aspartate + ATP → Argininosuccinate + AMP + PPi

2.2 Catalytic Mechanism

The crystal structure of human ASS1 (PDB: 2NZ2), solved at 2.4 Å resolution, reveals the structural basis for catalysis (karlberg2008structureofhuman pages 2-3, karlberg2008structureofhuman pages 5-6). The mechanism proceeds through an ATP-dependent, two-step process. ATP binds to the nucleotide-binding domain, triggering a conformational change in which this domain approaches the synthetase domain in a hinge-like movement (lakhalnaouar2012leishmaniadonovaniargininosuccinate pages 2-3). In the human enzyme, the nucleophilic oxygen atom of citrulline is positioned approximately 4.8 Å from the ATP α-phosphate, considerably shorter than the 7.9 Å distance observed in bacterial ASS, suggesting that smaller conformational changes are required for catalysis in the human enzyme (karlberg2008structureofhuman pages 5-6). During catalysis, citrulline undergoes nucleophilic attack on the α-phosphate of ATP, forming a citrullyl-AMP intermediate, which is subsequently attacked by the amino group of aspartate to yield argininosuccinate.

Key active-site residues involved in substrate binding and catalysis include Glu270, Tyr282, Arg127, Asn123, Tyr87, and Ser189, which coordinate citrulline through salt bridges and hydrogen bonds (karlberg2008structureofhuman pages 5-6). Aspartate is coordinated by Asn123 and Thr119, while Gln40 forms a hydrogen bond with the adenine moiety of ATP (karlberg2008structureofhuman pages 5-6, karlberg2008structureofhuman pages 6-7). A conserved mammalian residue, Cys132, positioned approximately 10.1 Å from ATP, can undergo S-nitrosylation, providing a mechanism for feedback inhibition by nitric oxide (karlberg2008structureofhuman pages 5-6, diezfernandez2017mutationsinthe pages 22-27).

3. Structural Biology

3.1 Domain Architecture

Each ASS1 monomer comprises three distinct structural domains: (i) an N-terminal nucleotide-binding domain containing an ATP pyrophosphatase consensus sequence, (ii) a central synthetase domain that harbors the substrate-binding cavity for citrulline and aspartate, and (iii) a C-terminal α-helical oligomerization domain that mediates tetramerization (diezfernandez2017mutationsinthe pages 1-6, karlberg2008structureofhuman pages 3-5, lakhalnaouar2012leishmaniadonovaniargininosuccinate pages 2-3). The two catalytic domains are tightly integrated, with helices from the nucleotide-binding domain traversing through the synthetase domain core (karlberg2008structureofhuman pages 3-5).

3.2 Quaternary Structure

ASS1 functions as a homotetramer composed of two identical dimers (karlberg2008structureofhuman pages 3-5). The dimer interface is formed exclusively between synthetase domains and involves helices 10 and 11, strands 11 and 14, a β-hairpin (residues 84–87), and an extended loop (residues 198–202), stabilized by two sets of five salt bridges and numerous polar interactions (karlberg2008structureofhuman pages 3-5). The tetramer interface is primarily hydrophobic, formed by helices 11 and 12 from the synthetase domains and helix 14 from the C-terminal oligomerization tail, surrounding a solvent-filled central cavity (karlberg2008structureofhuman pages 3-5). Mutations affecting the oligomerization helix, such as p.Gly390Arg, abolish enzymatic activity, demonstrating the essential nature of the tetrameric assembly (diezfernandez2017mutationsinthe pages 1-6, diezfernandez2017mutationsinthe pages 10-14).

4. Subcellular Localization

4.1 Cytosolic Localization

ASS1 is primarily a cytosolic enzyme in most tissues (finnie2020investigatingass1and pages 100-105, lim2024ass1metabolicallycontributes pages 6-6). In the liver, it functions within the cytosol of periportal hepatocytes as part of the urea cycle, where it is highly expressed (finnie2020investigatingass1and pages 100-105, diezfernandez2017mutationsinthe pages 10-14). In the kidney, ASS1 is predominantly cytosolic and confined to proximal tubular epithelial cells across all three segments of the proximal tubule, with very low expression in the rest of the nephron (finnie2020investigatingass1and pages 100-105). In endothelial cells, ASS1 associates with caveolae at relatively low expression levels, where it supports nitric oxide synthesis by coupling with NOS isoforms (finnie2020investigatingass1and pages 100-105).

4.2 Nuclear Localization

A landmark 2024 study by Lim et al. in Nature Metabolism revealed that ASS1 also functions in the nucleus following DNA damage (lim2024ass1metabolicallycontributes pages 6-6, lim2024ass1metabolicallycontributes pages 4-5). Upon DNA damage induction (e.g., by doxorubicin), ASS1 is translocated to the nucleus via the importin IPO7 in a partially p53-dependent manner (lim2024ass1metabolicallycontributes pages 4-5, lim2024ass1metabolicallycontributes pages 2-3). In the nucleus, ASS1 is chromatin-bound and its binding intensifies upon DNA damage (lim2024ass1metabolicallycontributes pages 6-6).

5. Biological Pathways and Functions

The following table provides a comprehensive summary of the metabolic pathways and biological processes involving ASS1:

Pathway/Process	Role of ASS1	Tissue Context	Key Interacting Enzymes/Proteins	References
Urea cycle (ammonia detoxification)	Catalyzes the ATP-dependent condensation of citrulline and aspartate to form argininosuccinate, a rate-limiting cytosolic step of the urea cycle that supports ammonia disposal as urea.	Highest functional importance in liver, especially periportal hepatocytes; also relevant in inherited urea-cycle disease.	ASL, CPS1, OTC, ARG1	(karlberg2008structureofhuman pages 1-2, delage2010argininedeprivationand pages 2-3, diezfernandez2017mutationsinthe pages 10-14, diezfernandez2017mutationsinthe pages 14-18)
De novo arginine biosynthesis	Produces argininosuccinate for subsequent conversion to arginine, supporting endogenous arginine synthesis from citrulline and aspartate.	Broadly expressed across tissues; especially important in kidney for systemic arginine production and in liver for integrated nitrogen metabolism.	ASL, citrulline supply pathways	(fung2025arginineatthe pages 2-3, finnie2020investigatingass1and pages 100-105, sun2022argininosuccinatesynthase1 pages 1-2)
Citrulline-NO recycling cycle	Regenerates arginine from citrulline to sustain nitric oxide production; acts as a key control point in the citrulline-NO cycle.	Endothelial and other NO-producing cells; also relevant in liver injury contexts with NOS2 induction.	NOS isoforms, ASL, caveolae-associated partners	(delage2010argininedeprivationand pages 2-3, leung2012argininosuccinatesynthaseconditions pages 3-5, finnie2020investigatingass1and pages 100-105)
Aspartate competition/pyrimidine synthesis	Consumes aspartate for argininosuccinate synthesis; when ASS1 is lost or silenced, aspartate is redirected toward pyrimidine/nucleotide biosynthesis, promoting proliferation.	Especially prominent in ASS1-low or ASS1-silenced cancers.	Pyrimidine synthesis network, p53-linked metabolic regulators	(sun2022argininosuccinatesynthase1 pages 2-4, fung2025arginineatthe pages 9-10, rogers2022canonicalandnoncanonical pages 17-21, lim2024ass1metabolicallycontributes pages 6-6)
AMPK/lipid metabolism linkage	Couples ureagenesis and amino-acid catabolism to hepatic AMPK activation and lipid oxidation; ASS1 knockdown suppresses ureagenesis and AMPK signaling.	Liver, particularly fasting/protein catabolism metabolic states.	AMPK and downstream hepatic lipid metabolism effectors	(madiraju2016argininosuccinatesynthetaseregulates pages 5-5)
Nuclear DNA damage response (p53/SMARCC1)	After DNA damage, ASS1 accumulates in nucleus and cytosol; in nucleus it works with ASL to generate fumarate, promotes SMARCC1 succination, alters SWI/SNF complex behavior, and modulates p53-regulated cell-cycle transcription.	Demonstrated in cultured human cancer cells and supported by liver nuclear studies; relevant to tumor suppression and genome maintenance.	p53, IPO7, ASL, SMARCC1, SNF5, SWI/SNF chromatin-remodeling complex	(lim2024ass1metabolicallycontributes pages 6-6, lim2024ass1metabolicallycontributes pages 4-5, lim2024ass1metabolicallycontributes pages 1-2, lim2024ass1metabolicallycontributes pages 2-3, lim2024ass1metabolicallycontributes pages 7-8)
Circadian regulation of ureagenesis (CLOCK acetylation)	Undergoes rhythmic CLOCK/BMAL1-dependent acetylation at K165/K176, which inhibits ASS1 activity and drives circadian oscillation of ureagenesis and arginine-cycle metabolites.	Hepatocytes and mouse liver.	CLOCK, BMAL1, HDACs	(lin2017clockacetylatesass1 pages 8-9, lin2017clockacetylatesass1 pages 10-11, lin2017clockacetylatesass1 pages 3-4, lin2017clockacetylatesass1 pages 6-7, lin2017clockacetylatesass1 pages 4-5, lin2017clockacetylatesass1 pages 9-10)

Table: This table summarizes the major metabolic pathways and biological processes involving human ASS1, including canonical urea-cycle functions and newer non-canonical roles in nuclear DNA-damage signaling and circadian regulation. It is useful for functional annotation because it links ASS1 biochemistry to tissue context and interacting partners.

5.1 Urea Cycle

In the hepatic urea cycle, ASS1 catalyzes the cytosolic condensation of citrulline (produced from carbamoyl phosphate and ornithine in the mitochondria by OTC) with aspartate to generate argininosuccinate (karlberg2008structureofhuman pages 1-2, fung2025arginineatthe pages 2-3). This is the rate-limiting step of ureagenesis, which detoxifies neurotoxic ammonia by converting it to urea for renal excretion (delage2010argininedeprivationand pages 2-3, diezfernandez2017mutationsinthe pages 10-14). ASS1 expression is highest in periportal hepatocytes, consistent with the zonation pattern of urea cycle enzymes (diezfernandez2017mutationsinthe pages 10-14).

5.2 De Novo Arginine Biosynthesis

Beyond the liver, ASS1 operates together with argininosuccinate lyase (ASL) to convert citrulline and aspartate into arginine (fung2025arginineatthe pages 2-3, finnie2020investigatingass1and pages 100-105). The kidney is the primary site of systemic arginine production in the body, where proximal tubular cells express high levels of ASS1 to convert circulating citrulline (derived from intestinal metabolism of dietary glutamine) into arginine (finnie2020investigatingass1and pages 100-105, fung2025arginineatthe pages 2-3). ASS1 is widely expressed across healthy tissues and supports de novo arginine synthesis in most cell types (fung2025arginineatthe pages 2-3).

5.3 Citrulline-NO Recycling Cycle

In nitric oxide (NO)-producing cells, ASS1 participates in the citrulline-NO recycling cycle: nitric oxide synthases (NOS) convert arginine to NO and citrulline, and ASS1 regenerates arginine from citrulline, completing the cycle and sustaining NO production (fung2025arginineatthe pages 2-3, delage2010argininedeprivationand pages 2-3, leung2012argininosuccinatesynthaseconditions pages 3-5). ASS1 functions as a potential enzymatic "switch" that provides substrate for NOS-induced NO synthesis and may have a rate-limiting role in high-output NO generation (leung2012argininosuccinatesynthaseconditions pages 3-5). However, at the whole-body level, citrulline availability—rather than ASS1 activity per se—is the ultimate limiting factor for endogenous arginine and NO synthesis (delage2010argininedeprivationand pages 2-3).

5.4 Aspartate Partitioning and Pyrimidine Metabolism

ASS1 competes with pyrimidine/nucleotide biosynthesis pathways for cytosolic aspartate (sun2022argininosuccinatesynthase1 pages 2-4, fung2025arginineatthe pages 9-10, lim2024ass1metabolicallycontributes pages 6-6). When ASS1 is present and active, it diverts aspartate toward argininosuccinate synthesis; when ASS1 is silenced or lost, aspartate is redirected toward pyrimidine nucleotide synthesis, supporting increased cell proliferation and potentially contributing to nucleotide imbalance and mutagenesis (lim2024ass1metabolicallycontributes pages 6-6, rogers2022canonicalandnoncanonical pages 17-21).

5.5 AMPK and Hepatic Lipid Metabolism

Madiraju et al. (2016) demonstrated that ASS1 regulates hepatic AMPK, linking protein catabolism and ureagenesis to hepatic lipid metabolism (madiraju2016argininosuccinatesynthetaseregulates pages 5-5). ASS1 knockdown inhibits both ureagenesis and AMPK activity in the liver, suggesting that ASS1 contributes to a protein-sparing metabolic switch during fasting or caloric restriction by connecting amino acid flux to fatty acid oxidation (madiraju2016argininosuccinatesynthetaseregulates pages 5-5).

5.6 Nuclear DNA Damage Response

In 2024, Lim et al. discovered a non-canonical nuclear function for ASS1 in the p53-mediated DNA damage response (lim2024ass1metabolicallycontributes pages 6-6, lim2024ass1metabolicallycontributes pages 1-2). Following DNA damage, ASS1 expression is elevated in both the cytosol and nucleus with at least partial dependency on p53 (lim2024ass1metabolicallycontributes pages 1-2, lim2024ass1metabolicallycontributes pages 2-3). In the cytosol, ASS1 metabolically restrains cell cycle progression by restricting nucleotide synthesis through aspartate consumption (lim2024ass1metabolicallycontributes pages 6-6). In the nucleus, ASS1 cooperates with ASL to generate fumarate, which promotes succination of SMARCC1, a subunit of the SWI/SNF chromatin-remodeling complex (lim2024ass1metabolicallycontributes pages 6-6, lim2024ass1metabolicallycontributes pages 5-6). This succination destabilizes the SMARCC1–SNF5 interaction, reducing chromatin accessibility at a subset of p53-regulated cell cycle gene promoters and thereby decreasing their transcription (lim2024ass1metabolicallycontributes pages 6-6, lim2024ass1metabolicallycontributes pages 1-2). Loss of ASS1 results in decreased SMARCC1 succination, enhanced chromatin accessibility, increased DNA damage, and accelerated cell cycle progression, likely contributing to cancer mutagenesis (lim2024ass1metabolicallycontributes pages 6-6, lim2024ass1metabolicallycontributes pages 1-2).

5.7 Circadian Regulation of Ureagenesis

Lin et al. (2017) demonstrated that the circadian clock protein CLOCK, facilitated by BMAL1, directly acetylates ASS1 at lysine residues K165 and K176, inhibiting ASS1 enzymatic activity by up to 50% (lin2017clockacetylatesass1 pages 3-4, lin2017clockacetylatesass1 pages 6-7). This acetylation exhibits circadian oscillation in both human cells and mouse liver, driven by rhythmic CLOCK–ASS1 interaction, and is reversed by HDACs (lin2017clockacetylatesass1 pages 8-9, lin2017clockacetylatesass1 pages 4-5). This post-translational modification mechanism drives the circadian rhythm of ureagenesis without altering ASS1 mRNA or protein levels (lin2017clockacetylatesass1 pages 3-4, lin2017clockacetylatesass1 pages 9-10). Acetylation-defective mutants (K165R/K176R) maintain elevated enzymatic activity regardless of CLOCK status, confirming these residues as the critical regulatory sites (lin2017clockacetylatesass1 pages 7-8, lin2017clockacetylatesass1 pages 6-7).

6. Post-Translational Regulation

In addition to CLOCK-mediated acetylation at K165/K176, ASS1 is regulated by several other post-translational modifications. Cys132, a conserved mammalian residue, undergoes S-nitrosylation, which inactivates the enzyme and provides a feedback inhibition mechanism linking NO production to arginine biosynthesis (karlberg2008structureofhuman pages 5-6, diezfernandez2017mutationsinthe pages 22-27). Phosphorylation at Ser328 has also been identified as a post-translational modification site (diezfernandez2017mutationsinthe pages 22-27). The p53 tumor suppressor directly transactivates ASS1 expression in response to genotoxic stress, revealing transcriptional regulation linked to cellular stress responses (lim2024ass1metabolicallycontributes pages 2-3).

7. Disease Associations

7.1 Citrullinemia Type I (CTLN1)

Biallelic loss-of-function mutations in ASS1 cause citrullinemia type I (CTLN1), an autosomal recessive urea cycle disorder with an incidence of approximately 1 in 250,000 live births (ribas2022hyperammonemiaininherited pages 4-5). The clinical spectrum ranges from severe neonatal-onset disease with life-threatening hyperammonemia (lethargy, somnolence, feeding refusal, vomiting, cerebral edema, convulsions, and coma) to milder late-onset forms presenting with recurrent neurological symptoms or even asymptomatic biochemical abnormalities (diezfernandez2017mutationsinthe pages 10-14, diezfernandez2017mutationsinthe pages 14-18). Biochemically, CTLN1 is characterized by markedly elevated plasma citrulline (often >2000 μmol/L), elevated ammonia and glutamine, low plasma arginine, and urinary orotic aciduria (diezfernandez2017mutationsinthe pages 14-18, ribas2022hyperammonemiaininherited pages 4-5). Mutations affecting the oligomerization interface (e.g., p.Gly324Ser, p.Arg363 mutations) tend to cause neonatal-onset disease, while some missense mutations in less critical regions may permit residual activity and milder presentations (diezfernandez2017mutationsinthe pages 10-14).

7.2 Cancer and Arginine Auxotrophy

Many aggressive tumors silence ASS1 expression, rendering them arginine-auxotrophic—dependent on extracellular arginine for survival (rogers2022canonicalandnoncanonical pages 13-17, delage2010argininedeprivationand pages 3-5, sun2022argininosuccinatesynthase1 pages 1-2). ASS1 silencing occurs predominantly through epigenetic mechanisms, including CpG island hypermethylation of the ASS1 promoter, HIF-1α-mediated transcriptional repression under hypoxic conditions, METTL14-mediated N6-methyladenosine modification, and miRNA-mediated suppression (sun2022argininosuccinatesynthase1 pages 1-2, sun2022argininosuccinatesynthase1 pages 2-4, rogers2022canonicalandnoncanonical pages 21-25). Tumors with frequent ASS1 loss include melanoma, hepatocellular carcinoma, mesothelioma, sarcomas (up to 88%), renal cell carcinoma, pancreatic cancer, and prostate cancer (delage2010argininedeprivationand pages 3-5, rogers2022canonicalandnoncanonical pages 13-17). The loss of ASS1 redirects aspartate toward pyrimidine synthesis to support proliferation and simultaneously impairs NO-dependent tumor suppressive signaling (sun2022argininosuccinatesynthase1 pages 2-4).

This vulnerability is exploited therapeutically by arginine deprivation therapy using ADI-PEG20 (pegylated arginine deiminase from Mycoplasma), which degrades extracellular arginine and selectively kills ASS1-deficient cancer cells (delage2010argininedeprivationand pages 3-5, rogers2022canonicalandnoncanonical pages 17-21, sun2022argininosuccinatesynthase1 pages 4-5). ADI-PEG20 has been evaluated in clinical trials for malignant pleural mesothelioma, pancreatic adenocarcinoma, non-small cell lung cancer, and other ASS1-low tumor types (sun2022argininosuccinatesynthase1 pages 7-7, sun2022argininosuccinatesynthase1 pages 4-5). Resistance mechanisms include ASS1 re-expression via promoter demethylation, autophagy-mediated intracellular arginine recycling, and extracellular vesicle-mediated arginine provision from stromal fibroblasts (rogers2022canonicalandnoncanonical pages 21-25, rogers2022canonicalandnoncanonical pages 13-17).

8. Summary

ASS1 is a multifunctional metabolic enzyme whose primary role—the ATP-dependent condensation of citrulline and aspartate to form argininosuccinate—positions it at the nexus of nitrogen metabolism in humans. Operating principally in the cytosol, ASS1 is rate-limiting for the urea cycle, de novo arginine biosynthesis, and the citrulline-NO recycling pathway (fung2025arginineatthe pages 2-3, delage2010argininedeprivationand pages 2-3). Recent research has expanded the functional repertoire of ASS1 to include nuclear roles in the p53-mediated DNA damage response via fumarate-dependent chromatin remodeling (lim2024ass1metabolicallycontributes pages 6-6), circadian regulation of ureagenesis through CLOCK-mediated acetylation (lin2017clockacetylatesass1 pages 3-4), and coupling of ureagenesis to hepatic lipid metabolism through AMPK (madiraju2016argininosuccinatesynthetaseregulates pages 5-5). Loss of ASS1 function underlies the inherited metabolic disorder citrullinemia type I and creates a metabolic vulnerability in numerous cancers that has been therapeutically targeted through arginine deprivation strategies (ribas2022hyperammonemiaininherited pages 4-5, delage2010argininedeprivationand pages 3-5).

References

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(karlberg2008structureofhuman pages 1-2): Tobias Karlberg, Ruairi Collins, Susanne van den Berg, Alex Flores, Martin Hammarström, Martin Högbom, Lovisa Holmberg Schiavone, and Jonas Uppenberg. Structure of human argininosuccinate synthetase. Acta crystallographica. Section D, Biological crystallography, 64 Pt 3:279-86, Mar 2008. URL: https://doi.org/10.1107/s0907444907067455, doi:10.1107/s0907444907067455. This article has 56 citations.
(fung2025arginineatthe pages 2-3): Tak Shun Fung, Keun Woo Ryu, and Craig B Thompson. Arginine: at the crossroads of nitrogen metabolism. The EMBO Journal, 44:1275-1293, Feb 2025. URL: https://doi.org/10.1038/s44318-025-00379-3, doi:10.1038/s44318-025-00379-3. This article has 94 citations.
(karlberg2008structureofhuman pages 3-5): Tobias Karlberg, Ruairi Collins, Susanne van den Berg, Alex Flores, Martin Hammarström, Martin Högbom, Lovisa Holmberg Schiavone, and Jonas Uppenberg. Structure of human argininosuccinate synthetase. Acta crystallographica. Section D, Biological crystallography, 64 Pt 3:279-86, Mar 2008. URL: https://doi.org/10.1107/s0907444907067455, doi:10.1107/s0907444907067455. This article has 56 citations.
(lim2024ass1metabolicallycontributes pages 6-6): Lisha Qiu Jin Lim, Lital Adler, Emma Hajaj, Leandro R. Soria, Rotem Ben-Tov Perry, Naama Darzi, Ruchama Brody, Noa Furth, Michal Lichtenstein, Elizabeta Bab-Dinitz, Ziv Porat, Tevie Melman, Alexander Brandis, Sergey Malitsky, Maxim Itkin, Yael Aylon, Shifra Ben-Dor, Irit Orr, Amir Pri-Or, Rony Seger, Yoav Shaul, Eytan Ruppin, Moshe Oren, Minervo Perez, Jordan Meier, Nicola Brunetti-Pierri, Efrat Shema, Igor Ulitsky, and Ayelet Erez. Ass1 metabolically contributes to the nuclear and cytosolic p53-mediated dna damage response. Nature Metabolism, 6:1294-1309, Jun 2024. URL: https://doi.org/10.1038/s42255-024-01060-5, doi:10.1038/s42255-024-01060-5. This article has 38 citations and is from a domain leading peer-reviewed journal.
(finnie2020investigatingass1and pages 100-105): Sarah Louise Finnie. Investigating ass1 and its role in renal fibrosis. ArXiv, Jun 2020. URL: https://doi.org/10.7488/era/258, doi:10.7488/era/258. This article has 0 citations.
(karlberg2008structureofhuman pages 5-6): Tobias Karlberg, Ruairi Collins, Susanne van den Berg, Alex Flores, Martin Hammarström, Martin Högbom, Lovisa Holmberg Schiavone, and Jonas Uppenberg. Structure of human argininosuccinate synthetase. Acta crystallographica. Section D, Biological crystallography, 64 Pt 3:279-86, Mar 2008. URL: https://doi.org/10.1107/s0907444907067455, doi:10.1107/s0907444907067455. This article has 56 citations.
(delage2010argininedeprivationand pages 2-3): Barbara Delage, Dean A. Fennell, Linda Nicholson, Iain McNeish, Nicholas R. Lemoine, Tim Crook, and Peter W. Szlosarek. Arginine deprivation and argininosuccinate synthetase expression in the treatment of cancer. International Journal of Cancer, 126:2762-2772, Jun 2010. URL: https://doi.org/10.1002/ijc.25202, doi:10.1002/ijc.25202. This article has 524 citations and is from a domain leading peer-reviewed journal.
(karlberg2008structureofhuman pages 6-7): Tobias Karlberg, Ruairi Collins, Susanne van den Berg, Alex Flores, Martin Hammarström, Martin Högbom, Lovisa Holmberg Schiavone, and Jonas Uppenberg. Structure of human argininosuccinate synthetase. Acta crystallographica. Section D, Biological crystallography, 64 Pt 3:279-86, Mar 2008. URL: https://doi.org/10.1107/s0907444907067455, doi:10.1107/s0907444907067455. This article has 56 citations.
(lin2017clockacetylatesass1 pages 8-9): Ran Lin, Yan Mo, Haihong Zha, Zhipeng Qu, Pancheng Xie, Zheng-Jiang Zhu, Ying Xu, Yue Xiong, and Kun-Liang Guan. Clock acetylates ass1 to drive circadian rhythm of ureagenesis. Molecular cell, 68 1:198-209.e6, Oct 2017. URL: https://doi.org/10.1016/j.molcel.2017.09.008, doi:10.1016/j.molcel.2017.09.008. This article has 84 citations and is from a highest quality peer-reviewed journal.
(lin2017clockacetylatesass1 pages 3-4): Ran Lin, Yan Mo, Haihong Zha, Zhipeng Qu, Pancheng Xie, Zheng-Jiang Zhu, Ying Xu, Yue Xiong, and Kun-Liang Guan. Clock acetylates ass1 to drive circadian rhythm of ureagenesis. Molecular cell, 68 1:198-209.e6, Oct 2017. URL: https://doi.org/10.1016/j.molcel.2017.09.008, doi:10.1016/j.molcel.2017.09.008. This article has 84 citations and is from a highest quality peer-reviewed journal.
(lin2017clockacetylatesass1 pages 6-7): Ran Lin, Yan Mo, Haihong Zha, Zhipeng Qu, Pancheng Xie, Zheng-Jiang Zhu, Ying Xu, Yue Xiong, and Kun-Liang Guan. Clock acetylates ass1 to drive circadian rhythm of ureagenesis. Molecular cell, 68 1:198-209.e6, Oct 2017. URL: https://doi.org/10.1016/j.molcel.2017.09.008, doi:10.1016/j.molcel.2017.09.008. This article has 84 citations and is from a highest quality peer-reviewed journal.
(sun2022argininosuccinatesynthase1 pages 2-4): Naihui Sun and Xing Zhao. Argininosuccinate synthase 1, arginine deprivation therapy and cancer management. Frontiers in Pharmacology, Jul 2022. URL: https://doi.org/10.3389/fphar.2022.935553, doi:10.3389/fphar.2022.935553. This article has 47 citations.
(madiraju2016argininosuccinatesynthetaseregulates pages 5-5): Anila K. Madiraju, Tiago Alves, Xiaojian Zhao, Gary W. Cline, Dongyan Zhang, Sanjay Bhanot, Varman T. Samuel, Richard G. Kibbey, and Gerald I. Shulman. Argininosuccinate synthetase regulates hepatic ampk linking protein catabolism and ureagenesis to hepatic lipid metabolism. Proceedings of the National Academy of Sciences, 113:E3423-E3430, May 2016. URL: https://doi.org/10.1073/pnas.1606022113, doi:10.1073/pnas.1606022113. This article has 77 citations and is from a highest quality peer-reviewed journal.
(lim2024ass1metabolicallycontributes pages 4-5): Lisha Qiu Jin Lim, Lital Adler, Emma Hajaj, Leandro R. Soria, Rotem Ben-Tov Perry, Naama Darzi, Ruchama Brody, Noa Furth, Michal Lichtenstein, Elizabeta Bab-Dinitz, Ziv Porat, Tevie Melman, Alexander Brandis, Sergey Malitsky, Maxim Itkin, Yael Aylon, Shifra Ben-Dor, Irit Orr, Amir Pri-Or, Rony Seger, Yoav Shaul, Eytan Ruppin, Moshe Oren, Minervo Perez, Jordan Meier, Nicola Brunetti-Pierri, Efrat Shema, Igor Ulitsky, and Ayelet Erez. Ass1 metabolically contributes to the nuclear and cytosolic p53-mediated dna damage response. Nature Metabolism, 6:1294-1309, Jun 2024. URL: https://doi.org/10.1038/s42255-024-01060-5, doi:10.1038/s42255-024-01060-5. This article has 38 citations and is from a domain leading peer-reviewed journal.
(diezfernandez2017mutationsinthe pages 10-14): Carmen Diez-Fernandez, Véronique Rüfenacht, and Johannes Häberle. Mutations in the human argininosuccinate synthetase (ass1) gene, impact on patients, common changes, and structural considerations. Human Mutation, 38:471-484, May 2017. URL: https://doi.org/10.1002/humu.23184, doi:10.1002/humu.23184. This article has 69 citations and is from a domain leading peer-reviewed journal.
(diezfernandez2017mutationsinthe pages 14-18): Carmen Diez-Fernandez, Véronique Rüfenacht, and Johannes Häberle. Mutations in the human argininosuccinate synthetase (ass1) gene, impact on patients, common changes, and structural considerations. Human Mutation, 38:471-484, May 2017. URL: https://doi.org/10.1002/humu.23184, doi:10.1002/humu.23184. This article has 69 citations and is from a domain leading peer-reviewed journal.
(ribas2022hyperammonemiaininherited pages 4-5): Graziela Schmitt Ribas, Franciele Fátima Lopes, Marion Deon, and Carmen Regla Vargas. Hyperammonemia in inherited metabolic diseases. Cellular and Molecular Neurobiology, 42:2593-2610, Oct 2022. URL: https://doi.org/10.1007/s10571-021-01156-6, doi:10.1007/s10571-021-01156-6. This article has 92 citations and is from a peer-reviewed journal.
(rogers2022canonicalandnoncanonical pages 13-17): Canonical and Noncanonical Mechanisms of Resistance to Arginine Starvation in Cancer This article has 0 citations.
(delage2010argininedeprivationand pages 3-5): Barbara Delage, Dean A. Fennell, Linda Nicholson, Iain McNeish, Nicholas R. Lemoine, Tim Crook, and Peter W. Szlosarek. Arginine deprivation and argininosuccinate synthetase expression in the treatment of cancer. International Journal of Cancer, 126:2762-2772, Jun 2010. URL: https://doi.org/10.1002/ijc.25202, doi:10.1002/ijc.25202. This article has 524 citations and is from a domain leading peer-reviewed journal.
(diezfernandez2017mutationsinthe pages 22-27): Carmen Diez-Fernandez, Véronique Rüfenacht, and Johannes Häberle. Mutations in the human argininosuccinate synthetase (ass1) gene, impact on patients, common changes, and structural considerations. Human Mutation, 38:471-484, May 2017. URL: https://doi.org/10.1002/humu.23184, doi:10.1002/humu.23184. This article has 69 citations and is from a domain leading peer-reviewed journal.
(karlberg2008structureofhuman pages 2-3): Tobias Karlberg, Ruairi Collins, Susanne van den Berg, Alex Flores, Martin Hammarström, Martin Högbom, Lovisa Holmberg Schiavone, and Jonas Uppenberg. Structure of human argininosuccinate synthetase. Acta crystallographica. Section D, Biological crystallography, 64 Pt 3:279-86, Mar 2008. URL: https://doi.org/10.1107/s0907444907067455, doi:10.1107/s0907444907067455. This article has 56 citations.
(lakhalnaouar2012leishmaniadonovaniargininosuccinate pages 2-3): Ines Lakhal-Naouar, Armando Jardim, Rona Strasser, Shen Luo, Yukiko Kozakai, Hira L. Nakhasi, and Robert C. Duncan. Leishmania donovani argininosuccinate synthase is an active enzyme associated with parasite pathogenesis. PLoS Neglected Tropical Diseases, 6:e1849, Oct 2012. URL: https://doi.org/10.1371/journal.pntd.0001849, doi:10.1371/journal.pntd.0001849. This article has 25 citations and is from a domain leading peer-reviewed journal.
(lim2024ass1metabolicallycontributes pages 2-3): Lisha Qiu Jin Lim, Lital Adler, Emma Hajaj, Leandro R. Soria, Rotem Ben-Tov Perry, Naama Darzi, Ruchama Brody, Noa Furth, Michal Lichtenstein, Elizabeta Bab-Dinitz, Ziv Porat, Tevie Melman, Alexander Brandis, Sergey Malitsky, Maxim Itkin, Yael Aylon, Shifra Ben-Dor, Irit Orr, Amir Pri-Or, Rony Seger, Yoav Shaul, Eytan Ruppin, Moshe Oren, Minervo Perez, Jordan Meier, Nicola Brunetti-Pierri, Efrat Shema, Igor Ulitsky, and Ayelet Erez. Ass1 metabolically contributes to the nuclear and cytosolic p53-mediated dna damage response. Nature Metabolism, 6:1294-1309, Jun 2024. URL: https://doi.org/10.1038/s42255-024-01060-5, doi:10.1038/s42255-024-01060-5. This article has 38 citations and is from a domain leading peer-reviewed journal.
(sun2022argininosuccinatesynthase1 pages 1-2): Naihui Sun and Xing Zhao. Argininosuccinate synthase 1, arginine deprivation therapy and cancer management. Frontiers in Pharmacology, Jul 2022. URL: https://doi.org/10.3389/fphar.2022.935553, doi:10.3389/fphar.2022.935553. This article has 47 citations.
(leung2012argininosuccinatesynthaseconditions pages 3-5): Tung Ming Leung, Yongke Lu, Wei Yan, José A. Morón-Concepción, Stephen C. Ward, Xiaodong Ge, Laura Conde de la Rosa, and Natalia Nieto. Argininosuccinate synthase conditions the response to acute and chronic ethanol‐induced liver injury in mice. Hepatology, 55:1596-1609, May 2012. URL: https://doi.org/10.1002/hep.25543, doi:10.1002/hep.25543. This article has 75 citations and is from a highest quality peer-reviewed journal.
(fung2025arginineatthe pages 9-10): Tak Shun Fung, Keun Woo Ryu, and Craig B Thompson. Arginine: at the crossroads of nitrogen metabolism. The EMBO Journal, 44:1275-1293, Feb 2025. URL: https://doi.org/10.1038/s44318-025-00379-3, doi:10.1038/s44318-025-00379-3. This article has 94 citations.
(rogers2022canonicalandnoncanonical pages 17-21): Canonical and Noncanonical Mechanisms of Resistance to Arginine Starvation in Cancer This article has 0 citations.
(lim2024ass1metabolicallycontributes pages 1-2): Lisha Qiu Jin Lim, Lital Adler, Emma Hajaj, Leandro R. Soria, Rotem Ben-Tov Perry, Naama Darzi, Ruchama Brody, Noa Furth, Michal Lichtenstein, Elizabeta Bab-Dinitz, Ziv Porat, Tevie Melman, Alexander Brandis, Sergey Malitsky, Maxim Itkin, Yael Aylon, Shifra Ben-Dor, Irit Orr, Amir Pri-Or, Rony Seger, Yoav Shaul, Eytan Ruppin, Moshe Oren, Minervo Perez, Jordan Meier, Nicola Brunetti-Pierri, Efrat Shema, Igor Ulitsky, and Ayelet Erez. Ass1 metabolically contributes to the nuclear and cytosolic p53-mediated dna damage response. Nature Metabolism, 6:1294-1309, Jun 2024. URL: https://doi.org/10.1038/s42255-024-01060-5, doi:10.1038/s42255-024-01060-5. This article has 38 citations and is from a domain leading peer-reviewed journal.
(lim2024ass1metabolicallycontributes pages 7-8): Lisha Qiu Jin Lim, Lital Adler, Emma Hajaj, Leandro R. Soria, Rotem Ben-Tov Perry, Naama Darzi, Ruchama Brody, Noa Furth, Michal Lichtenstein, Elizabeta Bab-Dinitz, Ziv Porat, Tevie Melman, Alexander Brandis, Sergey Malitsky, Maxim Itkin, Yael Aylon, Shifra Ben-Dor, Irit Orr, Amir Pri-Or, Rony Seger, Yoav Shaul, Eytan Ruppin, Moshe Oren, Minervo Perez, Jordan Meier, Nicola Brunetti-Pierri, Efrat Shema, Igor Ulitsky, and Ayelet Erez. Ass1 metabolically contributes to the nuclear and cytosolic p53-mediated dna damage response. Nature Metabolism, 6:1294-1309, Jun 2024. URL: https://doi.org/10.1038/s42255-024-01060-5, doi:10.1038/s42255-024-01060-5. This article has 38 citations and is from a domain leading peer-reviewed journal.
(lin2017clockacetylatesass1 pages 10-11): Ran Lin, Yan Mo, Haihong Zha, Zhipeng Qu, Pancheng Xie, Zheng-Jiang Zhu, Ying Xu, Yue Xiong, and Kun-Liang Guan. Clock acetylates ass1 to drive circadian rhythm of ureagenesis. Molecular cell, 68 1:198-209.e6, Oct 2017. URL: https://doi.org/10.1016/j.molcel.2017.09.008, doi:10.1016/j.molcel.2017.09.008. This article has 84 citations and is from a highest quality peer-reviewed journal.
(lin2017clockacetylatesass1 pages 4-5): Ran Lin, Yan Mo, Haihong Zha, Zhipeng Qu, Pancheng Xie, Zheng-Jiang Zhu, Ying Xu, Yue Xiong, and Kun-Liang Guan. Clock acetylates ass1 to drive circadian rhythm of ureagenesis. Molecular cell, 68 1:198-209.e6, Oct 2017. URL: https://doi.org/10.1016/j.molcel.2017.09.008, doi:10.1016/j.molcel.2017.09.008. This article has 84 citations and is from a highest quality peer-reviewed journal.
(lin2017clockacetylatesass1 pages 9-10): Ran Lin, Yan Mo, Haihong Zha, Zhipeng Qu, Pancheng Xie, Zheng-Jiang Zhu, Ying Xu, Yue Xiong, and Kun-Liang Guan. Clock acetylates ass1 to drive circadian rhythm of ureagenesis. Molecular cell, 68 1:198-209.e6, Oct 2017. URL: https://doi.org/10.1016/j.molcel.2017.09.008, doi:10.1016/j.molcel.2017.09.008. This article has 84 citations and is from a highest quality peer-reviewed journal.
(lim2024ass1metabolicallycontributes pages 5-6): Lisha Qiu Jin Lim, Lital Adler, Emma Hajaj, Leandro R. Soria, Rotem Ben-Tov Perry, Naama Darzi, Ruchama Brody, Noa Furth, Michal Lichtenstein, Elizabeta Bab-Dinitz, Ziv Porat, Tevie Melman, Alexander Brandis, Sergey Malitsky, Maxim Itkin, Yael Aylon, Shifra Ben-Dor, Irit Orr, Amir Pri-Or, Rony Seger, Yoav Shaul, Eytan Ruppin, Moshe Oren, Minervo Perez, Jordan Meier, Nicola Brunetti-Pierri, Efrat Shema, Igor Ulitsky, and Ayelet Erez. Ass1 metabolically contributes to the nuclear and cytosolic p53-mediated dna damage response. Nature Metabolism, 6:1294-1309, Jun 2024. URL: https://doi.org/10.1038/s42255-024-01060-5, doi:10.1038/s42255-024-01060-5. This article has 38 citations and is from a domain leading peer-reviewed journal.
(lin2017clockacetylatesass1 pages 7-8): Ran Lin, Yan Mo, Haihong Zha, Zhipeng Qu, Pancheng Xie, Zheng-Jiang Zhu, Ying Xu, Yue Xiong, and Kun-Liang Guan. Clock acetylates ass1 to drive circadian rhythm of ureagenesis. Molecular cell, 68 1:198-209.e6, Oct 2017. URL: https://doi.org/10.1016/j.molcel.2017.09.008, doi:10.1016/j.molcel.2017.09.008. This article has 84 citations and is from a highest quality peer-reviewed journal.
(rogers2022canonicalandnoncanonical pages 21-25): Canonical and Noncanonical Mechanisms of Resistance to Arginine Starvation in Cancer This article has 0 citations.
(sun2022argininosuccinatesynthase1 pages 4-5): Naihui Sun and Xing Zhao. Argininosuccinate synthase 1, arginine deprivation therapy and cancer management. Frontiers in Pharmacology, Jul 2022. URL: https://doi.org/10.3389/fphar.2022.935553, doi:10.3389/fphar.2022.935553. This article has 47 citations.
(sun2022argininosuccinatesynthase1 pages 7-7): Naihui Sun and Xing Zhao. Argininosuccinate synthase 1, arginine deprivation therapy and cancer management. Frontiers in Pharmacology, Jul 2022. URL: https://doi.org/10.3389/fphar.2022.935553, doi:10.3389/fphar.2022.935553. This article has 47 citations.

Artifacts

Citations

karlberg2008structureofhuman pages 1-2
diezfernandez2017mutationsinthe pages 1-6
diezfernandez2017mutationsinthe pages 22-27
delage2010argininedeprivationand pages 2-3
lakhalnaouar2012leishmaniadonovaniargininosuccinate pages 2-3
karlberg2008structureofhuman pages 5-6
karlberg2008structureofhuman pages 3-5
madiraju2016argininosuccinatesynthetaseregulates pages 5-5
diezfernandez2017mutationsinthe pages 10-14
fung2025arginineatthe pages 2-3
leung2012argininosuccinatesynthaseconditions pages 3-5
ribas2022hyperammonemiaininherited pages 4-5
karlberg2008structureofhuman pages 6-7
diezfernandez2017mutationsinthe pages 14-18
rogers2022canonicalandnoncanonical pages 13-17
delage2010argininedeprivationand pages 3-5
karlberg2008structureofhuman pages 2-3
fung2025arginineatthe pages 9-10
rogers2022canonicalandnoncanonical pages 17-21
rogers2022canonicalandnoncanonical pages 21-25
https://doi.org/10.1002/humu.23184,
https://doi.org/10.1107/s0907444907067455,
https://doi.org/10.1038/s44318-025-00379-3,
https://doi.org/10.1038/s42255-024-01060-5,
https://doi.org/10.7488/era/258,
https://doi.org/10.1002/ijc.25202,
https://doi.org/10.1016/j.molcel.2017.09.008,
https://doi.org/10.3389/fphar.2022.935553,
https://doi.org/10.1073/pnas.1606022113,
https://doi.org/10.1007/s10571-021-01156-6,
https://doi.org/10.1371/journal.pntd.0001849,
https://doi.org/10.1002/hep.25543,

📄 View Raw YAML

id: P00966
gene_symbol: ASS1
product_type: PROTEIN
status: DRAFT
taxon:
  id: NCBITaxon:9606
  label: Homo sapiens
description: >-
  ASS1 encodes argininosuccinate synthase (EC 6.3.4.5), a cytosolic homotetrameric
  ligase that catalyzes the ATP-dependent condensation of L-citrulline and L-aspartate
  to form argininosuccinate, AMP and diphosphate. This is the rate-limiting and committed
  step of de novo L-arginine biosynthesis and the third step of the hepatic urea cycle,
  where aspartate serves as the second nitrogen donor and the reaction feeds argininosuccinate
  to argininosuccinate lyase (ASL) for cleavage to arginine and fumarate. In the liver
  the enzyme is central to the disposal of ammonia as urea; in most extrahepatic tissues,
  ASS1 acting together with ASL regenerates arginine from citrulline (the citrulline-arginine
  cycle) and supplies arginine as substrate for nitric oxide synthases (the citrulline-NO
  cycle), notably in vascular endothelium and immune cells. Enzyme activity is modulated
  post-translationally, including inhibitory acetylation of Lys165/Lys176 that imposes a
  circadian rhythm on ureagenesis. Loss-of-function ASS1 variants cause citrullinemia type I
  (CTLN1), an autosomal recessive urea cycle disorder with hyperammonemia, elevated plasma
  citrulline and low arginine.
existing_annotations:
- term:
    id: GO:0004055
    label: argininosuccinate synthase activity
  evidence_type: IBA
  original_reference_id: GO_REF:0000033
  qualifier: enables
  review:
    summary: >-
      Phylogenetically inferred core molecular function. This is the correct and well-supported
      catalytic activity for ASS1 (EC 6.3.4.5), the enzyme name itself, and is confirmed by
      direct enzymology of the human recombinant protein.
    action: ACCEPT
    reason: >-
      IBA at exactly the right level of specificity for the family and directly corroborated by
      human experimental data. This is a defining core function.
    supported_by:
      - reference_id: PMID:8792870
        supporting_text: "Argininosuccinate synthetase (ASS) is a urea cycle enzyme with a tetrameric"
- term:
    id: GO:0005829
    label: cytosol
  evidence_type: IBA
  original_reference_id: GO_REF:0000033
  qualifier: is_active_in
  review:
    summary: >-
      Phylogenetically inferred cytosolic localization. ASS1 is a soluble cytosolic enzyme; the
      substrate citrulline is exported from mitochondria and converted in the cytosol.
    action: ACCEPT
    reason: >-
      Consistent with UniProt subcellular location (Cytoplasm, cytosol) and with direct
      immunofluorescence/experimental evidence. Correct compartment for a core function.
- term:
    id: GO:0006526
    label: L-arginine biosynthetic process
  evidence_type: IBA
  original_reference_id: GO_REF:0000033
  qualifier: involved_in
  review:
    summary: >-
      Phylogenetically inferred role in L-arginine biosynthesis. ASS1 with ASL performs the two
      steps that convert citrulline to arginine, making arginine available in most tissues.
    action: ACCEPT
    reason: >-
      Core biological process, matching UniProt PATHWAY annotation (L-arginine biosynthesis, step
      2/3) and experimental patient/expression data. IBA at appropriate specificity.
    supported_by:
      - reference_id: PMID:8792870
        supporting_text: "Argininosuccinate synthetase (ASS) is a urea cycle enzyme with a tetrameric"
- term:
    id: GO:0000050
    label: urea cycle
  evidence_type: IBA
  original_reference_id: GO_REF:0000033
  qualifier: involved_in
  review:
    summary: >-
      Phylogenetically inferred participation in the urea cycle, the metabolic step condensing
      citrulline and aspartate to argininosuccinate. This is a core biological process for the
      hepatic enzyme.
    action: ACCEPT
    reason: >-
      Well supported by human enzymology and disease genetics; ASS1 deficiency is the cause of
      citrullinemia type I, a urea cycle disorder. IBA correct.
    supported_by:
      - reference_id: PMID:8792870
        supporting_text: "Argininosuccinate synthetase (ASS) is a urea cycle enzyme with a tetrameric"
- term:
    id: GO:0004055
    label: argininosuccinate synthase activity
  evidence_type: IEA
  original_reference_id: GO_REF:0000120
  qualifier: enables
  review:
    summary: >-
      Automated (multiple IEA methods) assignment of the core catalytic activity, backed by
      InterPro signatures, RHEA:10932 and EC 6.3.4.5. Fully consistent with the experimental
      activity.
    action: ACCEPT
    reason: >-
      Redundant with the IBA/IMP argininosuccinate synthase activity annotations but correct; the
      EC/RHEA/InterPro mapping is accurate for this enzyme.
    supported_by:
      - reference_id: PMID:18473344
        supporting_text: "caused by deficiency of the urea cycle enzyme argininosuccinate synthetase"
- term:
    id: GO:0005524
    label: ATP binding
  evidence_type: IEA
  original_reference_id: GO_REF:0000002
  qualifier: enables
  review:
    summary: >-
      InterPro2GO mapping of ATP binding. ASS1 uses ATP as a co-substrate (activating citrulline
      via a citrullyl-AMP intermediate), and UniProt documents an ATP-binding SSGGxDS motif and
      ATP-binding feature/keyword.
    action: ACCEPT
    reason: >-
      Correct molecular function supported by the catalyzed reaction (ATP -> AMP + PPi) and by
      UniProt nucleotide-binding features; a genuine ligand-binding activity underpinning catalysis.
- term:
    id: GO:0005829
    label: cytosol
  evidence_type: IEA
  original_reference_id: GO_REF:0000044
  qualifier: located_in
  review:
    summary: >-
      Subcellular-location keyword mapping to cytosol from UniProt SL-0091.
    action: ACCEPT
    reason: >-
      Consistent with the experimentally supported cytosolic localization; redundant but correct.
- term:
    id: GO:0006526
    label: L-arginine biosynthetic process
  evidence_type: IEA
  original_reference_id: GO_REF:0000120
  qualifier: involved_in
  review:
    summary: >-
      Automated assignment of the L-arginine biosynthetic process, matching UniPathway UPA00068.
    action: ACCEPT
    reason: >-
      Correct core process, redundant with the IBA/IMP annotations.
- term:
    id: GO:0005515
    label: protein binding
  evidence_type: IPI
  original_reference_id: PMID:12620389
  qualifier: enables
  review:
    summary: >-
      IntAct-curated interaction with ARAF (Raf kinase) found in an exhaustive yeast two-hybrid
      screen. "protein binding" is uninformative and this is a high-throughput two-hybrid hit with
      no established biological consequence for ASS1.
    action: REMOVE
    reason: >-
      Per curation guidelines, bare "protein binding" (GO:0005515) is uninformative and should be
      avoided. The interaction is a screen-derived putative binary interaction (A-Raf/C-Raf Y2H
      atlas) not connected to ASS1 function; it adds no functional information to the review.
    supported_by:
      - reference_id: PMID:12620389
        supporting_text: "We have performed an exhaustive unbiased yeast two-hybrid analysis to identify"
- term:
    id: GO:0005515
    label: protein binding
  evidence_type: IPI
  original_reference_id: PMID:17496144
  qualifier: enables
  review:
    summary: >-
      IntAct-curated interaction with NMRAL1 (HSCARG, an NADP(H)-sensing redox protein). UniProt
      records this interaction, and NMRAL1 has been reported to regulate ASS1 activity. However
      the GO term captured is only the uninformative "protein binding".
    action: REMOVE
    reason: >-
      Bare "protein binding" is uninformative and discouraged. The underlying NMRAL1 interaction is
      real and biologically noted (redox regulation of ASS1), but the informative content belongs
      in a specific term or in the description, not in GO:0005515. The interaction itself is
      retained conceptually via UniProt SUBUNIT and is not lost.
    supported_by:
      - reference_id: PMID:17496144
        supporting_text: "may be argininosuccinate"
- term:
    id: GO:0005515
    label: protein binding
  evidence_type: IPI
  original_reference_id: PMID:28587924
  qualifier: enables
  review:
    summary: >-
      IntAct-curated interaction with PRMT7 (protein arginine methyltransferase 7), a direct
      interactor identified by Y2H and confirmed by pull-down; citrullinemia mutations disrupt the
      interaction. Captured only as uninformative "protein binding".
    action: REMOVE
    reason: >-
      Bare "protein binding" is discouraged. The PRMT7-ASS1 interaction is a genuine and
      interesting finding, but the GO term is uninformative; the biology is retained in the
      description and could be captured by a specific term if warranted. No functional information
      is lost by removing GO:0005515.
    supported_by:
      - reference_id: PMID:28587924
        supporting_text: "interacts with ASS1 using pull-down studies."
- term:
    id: GO:0042802
    label: identical protein binding
  evidence_type: IPI
  original_reference_id: PMID:16189514
  qualifier: enables
  review:
    summary: >-
      Self-interaction (ASS1-ASS1) consistent with the well-established homotetrameric quaternary
      structure of the enzyme.
    action: ACCEPT
    reason: >-
      "identical protein binding" is informative here: ASS1 is a homotetramer composed of identical
      subunits, so self-association is a bona fide, functionally meaningful property (the active
      enzyme is the tetramer). Multiple independent interactome studies report the self-interaction.
    supported_by:
      - reference_id: PMID:8792870
        supporting_text: "Argininosuccinate synthetase (ASS) is a urea cycle enzyme with a tetrameric"
- term:
    id: GO:0042802
    label: identical protein binding
  evidence_type: IPI
  original_reference_id: PMID:21988832
  qualifier: enables
  review:
    summary: >-
      Self-interaction detected in a human liver protein-interaction network study, consistent with
      the homotetrameric architecture of ASS1.
    action: ACCEPT
    reason: >-
      Corroborates the homotetramer; "identical protein binding" is a meaningful function for this
      obligate oligomer.
    supported_by:
      - reference_id: PMID:8792870
        supporting_text: "Argininosuccinate synthetase (ASS) is a urea cycle enzyme with a tetrameric"
- term:
    id: GO:0042802
    label: identical protein binding
  evidence_type: IPI
  original_reference_id: PMID:25416956
  qualifier: enables
  review:
    summary: >-
      Self-interaction from a proteome-scale human interactome map, again consistent with the
      homotetramer.
    action: ACCEPT
    reason: >-
      Reinforces the biologically meaningful homo-oligomerization of ASS1.
    supported_by:
      - reference_id: PMID:8792870
        supporting_text: "Argininosuccinate synthetase (ASS) is a urea cycle enzyme with a tetrameric"
- term:
    id: GO:0000050
    label: urea cycle
  evidence_type: IEA
  original_reference_id: GO_REF:0000120
  qualifier: involved_in
  review:
    summary: >-
      Automated urea cycle assignment, matching UniPathway UPA00158.
    action: ACCEPT
    reason: >-
      Correct core process, redundant with IBA and multiple experimental IMP annotations.
- term:
    id: GO:0001822
    label: kidney development
  evidence_type: IEA
  original_reference_id: GO_REF:0000107
  qualifier: involved_in
  review:
    summary: >-
      Ensembl-Compara ortholog-transfer from rat. ASS1 is expressed in fetal kidney and is part of
      the intestinal-renal citrulline-arginine axis, but a direct role in kidney developmental
      morphogenesis is not established for the human enzyme; this reads as an expression/context
      annotation rather than a developmental function.
    action: KEEP_AS_NON_CORE
    reason: >-
      Ortholog-transfer IEA reflecting a tissue in which ASS1 is expressed and active rather than a
      core molecular role in organ development. Not a core function; retain as non-core pending
      direct evidence.
- term:
    id: GO:0001889
    label: liver development
  evidence_type: IEA
  original_reference_id: GO_REF:0000107
  qualifier: involved_in
  review:
    summary: >-
      Ensembl-Compara ortholog-transfer from rat. ASS1 is the principal hepatic urea-cycle enzyme
      and is developmentally regulated in fetal liver, but "liver development" (organ
      morphogenesis) overstates its role; its liver function is metabolic (ureagenesis).
    action: KEEP_AS_NON_CORE
    reason: >-
      Ortholog-transfer IEA describing the tissue context (liver) of ASS1 expression rather than a
      causal role in liver organogenesis. Retain as non-core; the metabolic role is captured by the
      urea cycle / arginine biosynthesis annotations.
- term:
    id: GO:0005739
    label: mitochondrion
  evidence_type: IEA
  original_reference_id: GO_REF:0000107
  qualifier: located_in
  review:
    summary: >-
      Ensembl-Compara ortholog-transfer (from mouse) placing ASS1 in the mitochondrion. This
      contradicts the well-established cytosolic localization of ASS1; the enzyme acts in the
      cytosol on citrulline exported from mitochondria.
    action: REMOVE
    reason: >-
      ASS1 is a soluble cytosolic enzyme (UniProt: Cytoplasm, cytosol; direct IDA cytosol
      annotations). Mitochondrial localization is an over-propagated ortholog-transfer IEA
      inconsistent with the human protein and with urea-cycle compartmentalization (only the
      upstream steps CPS1/OTC are mitochondrial).
- term:
    id: GO:0005741
    label: mitochondrial outer membrane
  evidence_type: IEA
  original_reference_id: GO_REF:0000107
  qualifier: located_in
  review:
    summary: >-
      Ensembl-Compara ortholog-transfer (from rat) placing ASS1 at the mitochondrial outer
      membrane. Inconsistent with the established cytosolic localization of the enzyme.
    action: REMOVE
    reason: >-
      Over-propagated ortholog-transfer IEA. ASS1 is cytosolic; there is no reliable evidence for
      the human enzyme residing at the mitochondrial outer membrane.
- term:
    id: GO:0006953
    label: acute-phase response
  evidence_type: IEA
  original_reference_id: GO_REF:0000107
  qualifier: involved_in
  review:
    summary: >-
      Ensembl-Compara ortholog-transfer from rat. Reflects transcriptional induction of ASS1 under
      inflammatory/cytokine stimulation rather than a direct molecular role in the acute-phase
      response.
    action: KEEP_AS_NON_CORE
    reason: >-
      Regulation-of-expression / stimulus-response context transferred from ortholog, not a core
      catalytic role. Retain as non-core.
- term:
    id: GO:0007494
    label: midgut development
  evidence_type: IEA
  original_reference_id: GO_REF:0000107
  qualifier: involved_in
  review:
    summary: >-
      Ensembl-Compara ortholog-transfer from rat. Likely reflects intestinal ASS1 expression
      (enterocytes contribute to systemic citrulline/arginine metabolism) rather than a role in gut
      morphogenesis.
    action: KEEP_AS_NON_CORE
    reason: >-
      Ortholog-transfer IEA describing an expression context, not a core developmental function of
      the human enzyme. Retain as non-core.
- term:
    id: GO:0007584
    label: response to nutrient
  evidence_type: IEA
  original_reference_id: GO_REF:0000107
  qualifier: involved_in
  review:
    summary: >-
      Ensembl-Compara ortholog-transfer from rat. ASS1 expression/activity responds to dietary
      protein and amino acid availability, but this is a stimulus-response context, not a core
      molecular function.
    action: KEEP_AS_NON_CORE
    reason: >-
      Physiologically plausible (urea-cycle flux tracks nitrogen load) but an ortholog-transfer
      response annotation rather than core function. Retain as non-core.
- term:
    id: GO:0007623
    label: circadian rhythm
  evidence_type: IEA
  original_reference_id: GO_REF:0000107
  qualifier: involved_in
  review:
    summary: >-
      Ensembl-Compara ortholog-transfer from mouse. This is corroborated by direct human/mouse
      evidence: CLOCK acetylates ASS1 (K165/K176) to inactivate it in a circadian manner, imposing
      a circadian rhythm on ureagenesis.
    action: KEEP_AS_NON_CORE
    reason: >-
      Supported by experiment (see the IDA circadian rhythm annotation, PMID:28985504), but this is
      a regulated-behavior/output context rather than ASS1's core catalytic function. Retain as
      non-core; redundant with the experimental annotation below.
    supported_by:
      - reference_id: PMID:28985504
        supporting_text: "ASS1 acetylation by CLOCK exhibits circadian oscillation"
- term:
    id: GO:0009410
    label: response to xenobiotic stimulus
  evidence_type: IEA
  original_reference_id: GO_REF:0000107
  qualifier: involved_in
  review:
    summary: >-
      Ensembl-Compara ortholog-transfer from rat, reflecting altered ASS1 expression on xenobiotic
      exposure. Stimulus-response context, not a core function.
    action: KEEP_AS_NON_CORE
    reason: >-
      Ortholog-transfer response annotation; retain as non-core.
- term:
    id: GO:0009636
    label: response to toxic substance
  evidence_type: IEA
  original_reference_id: GO_REF:0000107
  qualifier: involved_in
  review:
    summary: >-
      Ensembl-Compara ortholog-transfer from rat. A broad stimulus-response term reflecting
      expression changes; not a core molecular function.
    action: KEEP_AS_NON_CORE
    reason: >-
      Ortholog-transfer response annotation with no direct human evidence for a core role; retain
      as non-core.
- term:
    id: GO:0010043
    label: response to zinc ion
  evidence_type: IEA
  original_reference_id: GO_REF:0000107
  qualifier: involved_in
  review:
    summary: >-
      Ensembl-Compara ortholog-transfer from rat; a specific stimulus-response context.
    action: KEEP_AS_NON_CORE
    reason: >-
      Ortholog-transfer response annotation, not core function; retain as non-core.
- term:
    id: GO:0010046
    label: response to mycotoxin
  evidence_type: IEA
  original_reference_id: GO_REF:0000107
  qualifier: involved_in
  review:
    summary: >-
      Ensembl-Compara ortholog-transfer from rat; narrow stimulus-response context.
    action: KEEP_AS_NON_CORE
    reason: >-
      Ortholog-transfer response annotation, not core function; retain as non-core.
- term:
    id: GO:0014075
    label: response to amine
  evidence_type: IEA
  original_reference_id: GO_REF:0000107
  qualifier: involved_in
  review:
    summary: >-
      Ensembl-Compara ortholog-transfer from rat; stimulus-response context.
    action: KEEP_AS_NON_CORE
    reason: >-
      Ortholog-transfer response annotation, not core function; retain as non-core.
- term:
    id: GO:0015643
    label: toxic substance binding
  evidence_type: IEA
  original_reference_id: GO_REF:0000107
  qualifier: enables
  review:
    summary: >-
      Ensembl-Compara ortholog-transfer from rat asserting ASS1 "binds a toxic substance". There is
      no credible biochemical basis for treating ASS1 as a toxin-binding protein; ASS1 is a
      metabolic ligase. This is an anomalous, likely spuriously propagated molecular-function IEA.
    action: REMOVE
    reason: >-
      Biologically implausible for a cytosolic urea-cycle ligase; unsupported by any human evidence
      or by the enzyme's mechanism. The term definition ("Binding to a toxic substance, a poisonous
      substance that causes damage to biological systems") does not fit ASS1. Over-propagated
      ortholog-transfer IEA.
- term:
    id: GO:0032355
    label: response to estradiol
  evidence_type: IEA
  original_reference_id: GO_REF:0000107
  qualifier: involved_in
  review:
    summary: >-
      Ensembl-Compara ortholog-transfer from rat; hormone stimulus-response context.
    action: KEEP_AS_NON_CORE
    reason: >-
      Ortholog-transfer response annotation, not core function; retain as non-core.
- term:
    id: GO:0032496
    label: response to lipopolysaccharide
  evidence_type: IEA
  original_reference_id: GO_REF:0000107
  qualifier: involved_in
  review:
    summary: >-
      Ensembl-Compara ortholog-transfer from rat. ASS1 is induced with iNOS in inflammatory
      (LPS/cytokine) settings to supply arginine for NO production, so this context is plausible,
      but it is not a core function.
    action: KEEP_AS_NON_CORE
    reason: >-
      Ortholog-transfer response annotation consistent with the citrulline-NO cycle role in
      immune/inflammatory cells; retain as non-core.
- term:
    id: GO:0043025
    label: neuronal cell body
  evidence_type: IEA
  original_reference_id: GO_REF:0000107
  qualifier: located_in
  review:
    summary: >-
      Ensembl-Compara ortholog-transfer from rat placing ASS1 in the neuronal cell body. ASS1 is
      expressed in specific neurons (citrulline-NO cycle), and within a neuron it would be
      cytosolic; the specific location is an ortholog-transferred expression context.
    action: KEEP_AS_NON_CORE
    reason: >-
      Cell-type-specific localization transferred from ortholog; plausible for the tissue context
      but not the canonical/core cytosolic annotation. Retain as non-core.
- term:
    id: GO:0043200
    label: response to amino acid
  evidence_type: IEA
  original_reference_id: GO_REF:0000107
  qualifier: involved_in
  review:
    summary: >-
      Ensembl-Compara ortholog-transfer from rat; amino-acid stimulus-response context (ASS1
      expression/activity responds to substrate and amino acid availability).
    action: KEEP_AS_NON_CORE
    reason: >-
      Ortholog-transfer response annotation, not core function; retain as non-core.
- term:
    id: GO:0043204
    label: perikaryon
  evidence_type: IEA
  original_reference_id: GO_REF:0000107
  qualifier: located_in
  review:
    summary: >-
      Ensembl-Compara ortholog-transfer from rat placing ASS1 in the perikaryon (neuronal cell
      body cytoplasm). A cell-type-specific location transferred from ortholog.
    action: KEEP_AS_NON_CORE
    reason: >-
      Ortholog-transfer localization tied to a specific tissue context; not the canonical/core
      cytosol annotation. Retain as non-core.
- term:
    id: GO:0043434
    label: response to peptide hormone
  evidence_type: IEA
  original_reference_id: GO_REF:0000107
  qualifier: involved_in
  review:
    summary: >-
      Ensembl-Compara ortholog-transfer from rat; hormone stimulus-response context.
    action: KEEP_AS_NON_CORE
    reason: >-
      Ortholog-transfer response annotation, not core function; retain as non-core.
- term:
    id: GO:0048545
    label: response to steroid hormone
  evidence_type: IEA
  original_reference_id: GO_REF:0000107
  qualifier: involved_in
  review:
    summary: >-
      Ensembl-Compara ortholog-transfer from rat; steroid-hormone stimulus-response context (ASS1 is
      known to be glucocorticoid-inducible).
    action: KEEP_AS_NON_CORE
    reason: >-
      Ortholog-transfer response annotation, not core function; retain as non-core.
- term:
    id: GO:0051384
    label: response to glucocorticoid
  evidence_type: IEA
  original_reference_id: GO_REF:0000107
  qualifier: involved_in
  review:
    summary: >-
      Ensembl-Compara ortholog-transfer from rat. ASS1 transcription is induced by glucocorticoids
      (hepatic urea-cycle regulation), so this context is plausible.
    action: KEEP_AS_NON_CORE
    reason: >-
      Ortholog-transfer response annotation reflecting hormonal regulation of expression, not core
      catalytic function; retain as non-core.
- term:
    id: GO:0060416
    label: response to growth hormone
  evidence_type: IEA
  original_reference_id: GO_REF:0000107
  qualifier: involved_in
  review:
    summary: >-
      Ensembl-Compara ortholog-transfer from rat; hormone stimulus-response context.
    action: KEEP_AS_NON_CORE
    reason: >-
      Ortholog-transfer response annotation, not core function; retain as non-core.
- term:
    id: GO:0060539
    label: diaphragm development
  evidence_type: IEA
  original_reference_id: GO_REF:0000107
  qualifier: involved_in
  review:
    summary: >-
      Ensembl-Compara ortholog-transfer from rat. There is no established human evidence linking
      ASS1 to diaphragm morphogenesis; this reads as a weakly supported ortholog-transferred
      developmental annotation.
    action: KEEP_AS_NON_CORE
    reason: >-
      Ortholog-transfer developmental annotation lacking direct human support; not a core function.
      Retain as non-core rather than removing, deferring to the experimental source in the
      orthologous species.
- term:
    id: GO:0070542
    label: response to fatty acid
  evidence_type: IEA
  original_reference_id: GO_REF:0000107
  qualifier: involved_in
  review:
    summary: >-
      Ensembl-Compara ortholog-transfer from rat; stimulus-response context.
    action: KEEP_AS_NON_CORE
    reason: >-
      Ortholog-transfer response annotation, not core function; retain as non-core.
- term:
    id: GO:0070852
    label: cell body fiber
  evidence_type: IEA
  original_reference_id: GO_REF:0000107
  qualifier: located_in
  review:
    summary: >-
      Ensembl-Compara ortholog-transfer from rat; a neuronal cell-type-specific location.
    action: KEEP_AS_NON_CORE
    reason: >-
      Ortholog-transfer localization for a specific tissue context; not the canonical/core cytosol
      annotation. Retain as non-core.
- term:
    id: GO:0071222
    label: cellular response to lipopolysaccharide
  evidence_type: IEA
  original_reference_id: GO_REF:0000107
  qualifier: involved_in
  review:
    summary: >-
      Ensembl-Compara ortholog-transfer from rat; cellular stimulus-response context (inflammatory
      induction of ASS1 for arginine/NO supply).
    action: KEEP_AS_NON_CORE
    reason: >-
      Ortholog-transfer response annotation consistent with the citrulline-NO cycle in immune
      cells; retain as non-core.
- term:
    id: GO:0071230
    label: cellular response to amino acid stimulus
  evidence_type: IEA
  original_reference_id: GO_REF:0000107
  qualifier: involved_in
  review:
    summary: >-
      Ensembl-Compara ortholog-transfer from rat; amino-acid stimulus-response context.
    action: KEEP_AS_NON_CORE
    reason: >-
      Ortholog-transfer response annotation, not core function; retain as non-core.
- term:
    id: GO:0071242
    label: cellular response to ammonium ion
  evidence_type: IEA
  original_reference_id: GO_REF:0000107
  qualifier: involved_in
  review:
    summary: >-
      Ensembl-Compara ortholog-transfer from rat; stimulus-response context (ureagenesis responds
      to nitrogen/ammonia load).
    action: KEEP_AS_NON_CORE
    reason: >-
      Ortholog-transfer response annotation, not core function; retain as non-core.
- term:
    id: GO:0071320
    label: cellular response to cAMP
  evidence_type: IEA
  original_reference_id: GO_REF:0000107
  qualifier: involved_in
  review:
    summary: >-
      Ensembl-Compara ortholog-transfer from rat; second-messenger stimulus-response context.
    action: KEEP_AS_NON_CORE
    reason: >-
      Ortholog-transfer response annotation, not core function; retain as non-core.
- term:
    id: GO:0071346
    label: cellular response to type II interferon
  evidence_type: IEA
  original_reference_id: GO_REF:0000107
  qualifier: involved_in
  review:
    summary: >-
      Ensembl-Compara ortholog-transfer from rat; cytokine (IFN-gamma) stimulus-response context,
      consistent with immune induction of ASS1 for arginine/NO supply.
    action: KEEP_AS_NON_CORE
    reason: >-
      Ortholog-transfer response annotation, not core function; retain as non-core.
- term:
    id: GO:0071356
    label: cellular response to tumor necrosis factor
  evidence_type: IEA
  original_reference_id: GO_REF:0000107
  qualifier: involved_in
  review:
    summary: >-
      Ensembl-Compara ortholog-transfer from rat; cytokine (TNF) stimulus-response context. Related
      human work shows ASS1/NOS3 counteract TNF-alpha-stimulated monocyte adhesion in endothelium.
    action: KEEP_AS_NON_CORE
    reason: >-
      Ortholog-transfer response annotation, not core function; retain as non-core.
- term:
    id: GO:0071377
    label: cellular response to glucagon stimulus
  evidence_type: IEA
  original_reference_id: GO_REF:0000107
  qualifier: involved_in
  review:
    summary: >-
      Ensembl-Compara ortholog-transfer from rat; hormone stimulus-response context (glucagon
      induces hepatic urea-cycle enzymes).
    action: KEEP_AS_NON_CORE
    reason: >-
      Ortholog-transfer response annotation, not core function; retain as non-core.
- term:
    id: GO:0071400
    label: cellular response to oleic acid
  evidence_type: IEA
  original_reference_id: GO_REF:0000107
  qualifier: involved_in
  review:
    summary: >-
      Ensembl-Compara ortholog-transfer from rat; a narrow fatty-acid stimulus-response context.
    action: KEEP_AS_NON_CORE
    reason: >-
      Ortholog-transfer response annotation, not core function; retain as non-core.
- term:
    id: GO:0071418
    label: cellular response to amine stimulus
  evidence_type: IEA
  original_reference_id: GO_REF:0000107
  qualifier: involved_in
  review:
    summary: >-
      Ensembl-Compara ortholog-transfer from rat; amine stimulus-response context.
    action: KEEP_AS_NON_CORE
    reason: >-
      Ortholog-transfer response annotation, not core function; retain as non-core.
- term:
    id: GO:0071549
    label: cellular response to dexamethasone stimulus
  evidence_type: IEA
  original_reference_id: GO_REF:0000107
  qualifier: involved_in
  review:
    summary: >-
      Ensembl-Compara ortholog-transfer from rat; glucocorticoid (dexamethasone) stimulus-response
      context, consistent with glucocorticoid induction of ASS1.
    action: KEEP_AS_NON_CORE
    reason: >-
      Ortholog-transfer response annotation, not core function; retain as non-core.
- term:
    id: GO:0000050
    label: urea cycle
  evidence_type: IMP
  original_reference_id: PMID:7977368
  qualifier: involved_in
  review:
    summary: >-
      Experimental (IMP) urea cycle annotation based on characterization of citrullinemia-causing
      ASS1 mutations in patients. Loss of ASS1 function blocks the urea cycle, causing classic
      citrullinemia.
    action: ACCEPT
    reason: >-
      Directly supported by patient mutation genetics; a core biological process. Defer to the
      curator's full-text reading of the disease-gene relationship.
    supported_by:
      - reference_id: PMID:7977368
        supporting_text: "Citrullinemia is an autosomal recessive disease caused by a genetic deficiency"
- term:
    id: GO:0006533
    label: L-aspartate catabolic process
  evidence_type: IMP
  original_reference_id: PMID:7977368
  qualifier: involved_in
  review:
    summary: >-
      Experimental (IMP) annotation reflecting that ASS1 consumes L-aspartate (the second nitrogen
      donor) in the argininosuccinate synthase reaction. This is a curator reframing of the same
      catalytic step as an aspartate catabolic process.
    action: KEEP_AS_NON_CORE
    reason: >-
      Not incorrect (ASS1 does consume aspartate as a co-substrate), but it is a redundant,
      substrate-centric restatement of the core argininosuccinate synthase activity / urea cycle
      role rather than an independent biological process. Retain as non-core; defer to the
      experimental curator who read the full text.
    supported_by:
      - reference_id: PMID:7977368
        supporting_text: "Citrullinemia is an autosomal recessive disease caused by a genetic deficiency"
- term:
    id: GO:0019241
    label: L-citrulline catabolic process
  evidence_type: IMP
  original_reference_id: PMID:7977368
  qualifier: involved_in
  review:
    summary: >-
      Experimental (IMP) annotation reflecting that ASS1 consumes L-citrulline in the
      argininosuccinate synthase reaction; ASS1 deficiency causes citrulline accumulation. This is a
      substrate-centric reframing of the same catalytic step.
    action: KEEP_AS_NON_CORE
    reason: >-
      Not incorrect (citrulline is the substrate whose accumulation defines citrullinemia), but it
      is a redundant restatement of the core enzyme activity / arginine-biosynthesis and urea-cycle
      roles. Retain as non-core; defer to the experimental curator.
    supported_by:
      - reference_id: PMID:7977368
        supporting_text: "Citrullinemia is an autosomal recessive disease caused by a genetic deficiency"
- term:
    id: GO:0005829
    label: cytosol
  evidence_type: IDA
  original_reference_id: GO_REF:0000052
  qualifier: located_in
  review:
    summary: >-
      Direct immunofluorescence (Human Protein Atlas) localization to the cytosol.
    action: ACCEPT
    reason: >-
      Experimental confirmation of the core cytosolic localization of ASS1.
- term:
    id: GO:0005829
    label: cytosol
  evidence_type: TAS
  original_reference_id: Reactome:R-HSA-9956517
  qualifier: located_in
  review:
    summary: >-
      Reactome traceable-author-statement placing ASS1 (in the context of disease variants failing
      to synthesize argininosuccinate) in the cytosol.
    action: ACCEPT
    reason: >-
      Consistent with the established cytosolic localization; redundant but correct.
- term:
    id: GO:0004055
    label: argininosuccinate synthase activity
  evidence_type: IMP
  original_reference_id: PMID:28985504
  qualifier: enables
  review:
    summary: >-
      Experimental (IMP) support for ASS1 catalytic activity from the CLOCK-acetylation study,
      which manipulated ASS1 and measured its activity (acetylation of K165/K176 inactivates the
      enzyme).
    action: ACCEPT
    reason: >-
      Core molecular function directly assayed in the study; ASS1 "catalyzes the rate-limiting step
      of arginine biosynthesis".
    supported_by:
      - reference_id: PMID:28985504
        supporting_text: "synthase (ASS1) to inactivate ASS1, which catalyzes the rate-limiting step of"
- term:
    id: GO:0005515
    label: protein binding
  evidence_type: IPI
  original_reference_id: PMID:28985504
  qualifier: enables
  review:
    summary: >-
      IntAct/UniProt interaction with CLOCK (O15516) demonstrated in the circadian-ureagenesis
      study. Captured only as uninformative "protein binding".
    action: REMOVE
    reason: >-
      Bare "protein binding" is discouraged. The ASS1-CLOCK interaction is genuine and functionally
      important (CLOCK acetylates ASS1), but this content is retained in the description and in the
      circadian-rhythm annotation; the uninformative GO:0005515 term itself adds nothing.
    supported_by:
      - reference_id: PMID:28985504
        supporting_text: "CLOCK directly acetylates K165 and K176 of argininosuccinate"
- term:
    id: GO:0005829
    label: cytosol
  evidence_type: IDA
  original_reference_id: PMID:28985504
  qualifier: located_in
  review:
    summary: >-
      Direct experimental (IDA) cytosolic localization from the CLOCK-acetylation study; UniProt
      cites this paper for the Cytoplasm, cytosol subcellular location.
    action: ACCEPT
    reason: >-
      Experimental confirmation of the core cytosolic localization.
- term:
    id: GO:0007623
    label: circadian rhythm
  evidence_type: IDA
  original_reference_id: PMID:28985504
  qualifier: involved_in
  review:
    summary: >-
      Direct experimental (IDA) evidence that ASS1 activity is under circadian control: CLOCK
      acetylates ASS1 in a circadian manner, producing an oscillation in ASS1 activity and
      ureagenesis in human cells and mouse liver.
    action: KEEP_AS_NON_CORE
    reason: >-
      Well supported experimentally, but this describes a regulated output/behavior in which ASS1
      participates rather than ASS1's intrinsic core function. Retain as non-core.
    supported_by:
      - reference_id: PMID:28985504
        supporting_text: "ASS1 acetylation by CLOCK exhibits circadian oscillation"
- term:
    id: GO:0000050
    label: urea cycle
  evidence_type: IMP
  original_reference_id: PMID:8792870
  qualifier: involved_in
  review:
    summary: >-
      Experimental (IMP) urea cycle annotation from characterization of wild-type and mutant human
      ASS proteins; the paper explicitly frames ASS as a urea cycle enzyme and links mutations to
      citrullinemia.
    action: ACCEPT
    reason: >-
      Core biological process, directly supported by recombinant enzymology of the human protein.
    supported_by:
      - reference_id: PMID:8792870
        supporting_text: "Argininosuccinate synthetase (ASS) is a urea cycle enzyme with a tetrameric"
- term:
    id: GO:0004055
    label: argininosuccinate synthase activity
  evidence_type: IMP
  original_reference_id: PMID:8792870
  qualifier: enables
  review:
    summary: >-
      Experimental (IMP) measurement of ASS catalytic activity: purified recombinant wild-type
      human ASS matched native liver enzyme, and mutants showed reduced/abolished activity and
      abnormal kinetics (elevated Km for citrulline).
    action: ACCEPT
    reason: >-
      Direct biochemical characterization of the core molecular function of the human enzyme.
    supported_by:
      - reference_id: PMID:8792870
        supporting_text: "G280R mutant was extracted with an amount of ASS protein similar to wild-type"
- term:
    id: GO:0006526
    label: L-arginine biosynthetic process
  evidence_type: IMP
  original_reference_id: PMID:8792870
  qualifier: involved_in
  review:
    summary: >-
      Experimental (IMP) support for ASS1's role in arginine biosynthesis via the biochemical
      characterization of the enzyme that carries out the committed step.
    action: ACCEPT
    reason: >-
      Core biological process supported by the human enzymology; defer to the experimental curator.
    supported_by:
      - reference_id: PMID:8792870
        supporting_text: "Argininosuccinate synthetase (ASS) is a urea cycle enzyme with a tetrameric"
- term:
    id: GO:0000050
    label: urea cycle
  evidence_type: IMP
  original_reference_id: PMID:18473344
  qualifier: involved_in
  review:
    summary: >-
      Experimental (IMP) urea cycle annotation from in vitro expression/enzymology of CTLN1
      variants; the paper describes ASS as "the urea cycle enzyme argininosuccinate synthetase".
    action: ACCEPT
    reason: >-
      Core biological process supported by disease-variant enzymology.
    supported_by:
      - reference_id: PMID:18473344
        supporting_text: "caused by deficiency of the urea cycle enzyme argininosuccinate synthetase"
- term:
    id: GO:0004055
    label: argininosuccinate synthase activity
  evidence_type: IMP
  original_reference_id: PMID:18473344
  qualifier: enables
  review:
    summary: >-
      Experimental (IMP) enzymatic analysis of purified wild-type and mutant ASS proteins, with
      measured kinetic parameters (KM 112 uM citrulline, 68 uM aspartate) and reduced activity for
      pathogenic variants.
    action: ACCEPT
    reason: >-
      Direct measurement of the core catalytic activity; underpins the UniProt EC 6.3.4.5 and
      kinetic parameters.
    supported_by:
      - reference_id: PMID:18473344
        supporting_text: "enzymatic analysis of purified wild-type and the mutant ASS proteins"
- term:
    id: GO:0006526
    label: L-arginine biosynthetic process
  evidence_type: IMP
  original_reference_id: PMID:18473344
  qualifier: involved_in
  review:
    summary: >-
      Experimental (IMP) support for the arginine-biosynthesis role via enzymology of the ASS
      reaction, which produces argininosuccinate en route to arginine.
    action: ACCEPT
    reason: >-
      Core biological process supported by the human enzyme characterization.
    supported_by:
      - reference_id: PMID:18473344
        supporting_text: "caused by deficiency of the urea cycle enzyme argininosuccinate synthetase"
- term:
    id: GO:0000050
    label: urea cycle
  evidence_type: IMP
  original_reference_id: PMID:27287393
  qualifier: involved_in
  review:
    summary: >-
      Experimental (IMP) urea cycle annotation from characterization of 21 kinetic CTLN1 mutations;
      the paper frames citrullinemia type 1 as "an autosomal-recessive urea cycle disorder".
    action: ACCEPT
    reason: >-
      Core biological process supported by disease-mutation enzymology.
    supported_by:
      - reference_id: PMID:27287393
        supporting_text: "BACKGROUND: Citrullinemia type 1 is an autosomal-recessive urea cycle disorder"
- term:
    id: GO:0004055
    label: argininosuccinate synthase activity
  evidence_type: IMP
  original_reference_id: PMID:27287393
  qualifier: enables
  review:
    summary: >-
      Experimental (IMP) measurement of ASS catalytic activity and kinetics for 21 mutants by
      tandem mass spectrometry; 13 were inactive and 8 had decreased substrate affinity, rescuable
      by aspartate supplementation.
    action: ACCEPT
    reason: >-
      Direct quantitative measurement of the core molecular function of the human enzyme.
    supported_by:
      - reference_id: PMID:27287393
        supporting_text: "activity and kinetic parameters were measured using tandem mass spectrometry and"
- term:
    id: GO:0006526
    label: L-arginine biosynthetic process
  evidence_type: IMP
  original_reference_id: PMID:27287393
  qualifier: involved_in
  review:
    summary: >-
      Experimental (IMP) support for the arginine-biosynthesis role via kinetic characterization of
      the ASS reaction (citrulline + aspartate + ATP -> argininosuccinate).
    action: ACCEPT
    reason: >-
      Core biological process supported by the human enzyme kinetics.
    supported_by:
      - reference_id: PMID:27287393
        supporting_text: "map near the substrate (aspartate or citrulline)"
- term:
    id: GO:0070062
    label: extracellular exosome
  evidence_type: HDA
  original_reference_id: PMID:23533145
  qualifier: located_in
  review:
    summary: >-
      High-throughput detection of ASS1 peptides in urinary/prostatic exosome proteomes. This is a
      mass-spectrometry proteomic inventory, not evidence of a functional extracellular-vesicle
      localization for a cytosolic metabolic enzyme.
    action: KEEP_AS_NON_CORE
    reason: >-
      Abundant cytosolic enzymes are common background hits in exosome/secretome proteomics; the
      finding is real as a detection event but does not reflect a core functional localization.
      Retain as non-core rather than removing, since the peptide detection is genuine.
    supported_by:
      - reference_id: PMID:23533145
        supporting_text: "expressed prostatic secretions in urine (EPS-urine), exosome preparations were"
- term:
    id: GO:0004055
    label: argininosuccinate synthase activity
  evidence_type: IMP
  original_reference_id: PMID:7977368
  qualifier: enables
  review:
    summary: >-
      Experimental (IMP) support for the catalytic activity via mutation analysis in citrullinemia
      patients; the deficiency of ASS activity underlies the disease.
    action: ACCEPT
    reason: >-
      Core molecular function supported by patient genetics; defer to the experimental curator.
    supported_by:
      - reference_id: PMID:7977368
        supporting_text: "Citrullinemia is an autosomal recessive disease caused by a genetic deficiency"
- term:
    id: GO:0016597
    label: amino acid binding
  evidence_type: IMP
  original_reference_id: PMID:7977368
  qualifier: enables
  review:
    summary: >-
      Experimental (IMP) annotation of amino acid binding, reflecting that ASS1 binds its amino
      acid substrates L-citrulline and L-aspartate; several CTLN1 mutations map to the substrate
      (aspartate/citrulline) binding site and impair substrate affinity.
    action: ACCEPT
    reason: >-
      Informative molecular function distinct from the catalytic term: ASS1 has bona fide amino
      acid (citrulline/aspartate) binding sites (documented in UniProt BINDING features), and
      kinetic mutants show altered Km. Supported by the experimental mutation studies.
    supported_by:
      - reference_id: PMID:27287393
        supporting_text: "map near the substrate (aspartate or citrulline)"
- term:
    id: GO:0045429
    label: positive regulation of nitric oxide biosynthetic process
  evidence_type: IMP
  original_reference_id: PMID:21106532
  qualifier: involved_in
  review:
    summary: >-
      Experimental (IMP) evidence in endothelial cells that ASS1, by regenerating arginine (the
      NOS3 substrate) from citrulline, increases NO production; overexpression of ASS1 raised NO and
      ASS1/NOS3 siRNAs attenuated shear-stress-induced NO. This is the citrulline-NO cycle role.
    action: KEEP_AS_NON_CORE
    reason: >-
      Genuine, physiologically important extrahepatic function of ASS1 (supplying arginine for NO
      synthesis) but it is a downstream regulatory consequence of the core arginine-biosynthesis
      activity in a specific cell type, not the enzyme's intrinsic core function. Retain as
      non-core.
    supported_by:
      - reference_id: PMID:21106532
        supporting_text: "increased NO production and decreased monocyte adhesion stimulated by tumor"
- term:
    id: GO:0071499
    label: cellular response to laminar fluid shear stress
  evidence_type: IMP
  original_reference_id: PMID:21106532
  qualifier: involved_in
  review:
    summary: >-
      Experimental (IMP) evidence that laminar shear stress induces ASS1 in endothelial cells and
      that ASS1 (with NOS3) is required for the shear-stress-stimulated increase in NO production.
    action: KEEP_AS_NON_CORE
    reason: >-
      A cell-type-specific stimulus-response/physiological role, downstream of ASS1's core arginine
      supply function; not the enzyme's intrinsic core function. Retain as non-core.
    supported_by:
      - reference_id: PMID:21106532
        supporting_text: "SiRNAs of NOS3 and ASS1 attenuated"
- term:
    id: GO:1903038
    label: negative regulation of leukocyte cell-cell adhesion
  evidence_type: IMP
  original_reference_id: PMID:21106532
  qualifier: involved_in
  review:
    summary: >-
      Experimental (IMP) evidence that ASS1 (via NO production) reduces TNF-alpha-stimulated
      monocyte adhesion to endothelial cells, an anti-inflammatory endothelial effect downstream of
      arginine/NO supply.
    action: KEEP_AS_NON_CORE
    reason: >-
      A downstream physiological consequence of the endothelial citrulline-NO cycle role, mediated
      by NO rather than a direct ASS1 activity on adhesion; not a core function. Retain as
      non-core.
    supported_by:
      - reference_id: PMID:21106532
        supporting_text: "increased NO production and decreased monocyte adhesion stimulated by tumor"
- term:
    id: GO:0003723
    label: RNA binding
  evidence_type: HDA
  original_reference_id: PMID:22658674
  qualifier: enables
  review:
    summary: >-
      High-throughput "interactome capture" detection of ASS1 among mRNA-binding proteins in
      proliferating HeLa cells (mRNA interactome atlas). Many metabolic enzymes were unexpectedly
      captured; no dedicated RNA-binding function has been demonstrated for ASS1.
    action: MARK_AS_OVER_ANNOTATED
    reason: >-
      This derives from a single high-throughput RNA-interactome screen that recovered numerous
      "moonlighting" metabolic enzymes. There is no orthogonal validation of a functional
      RNA-binding role for ASS1, so it is very likely an over-annotation rather than a core or
      established secondary function. Flag as over-annotated rather than accepting.
    supported_by:
      - reference_id: PMID:22658674
        supporting_text: "RNA-binding enzymes of intermediary"
- term:
    id: GO:0070062
    label: extracellular exosome
  evidence_type: HDA
  original_reference_id: PMID:19056867
  qualifier: located_in
  review:
    summary: >-
      High-throughput detection of ASS1 in a large-scale urinary-exosome proteome. As above, an MS
      inventory hit for a cytosolic enzyme rather than evidence of a functional extracellular
      localization.
    action: KEEP_AS_NON_CORE
    reason: >-
      Genuine peptide detection in an exosome proteomics dataset, but not a core functional
      localization for this cytosolic urea-cycle enzyme. Retain as non-core.
    supported_by:
      - reference_id: PMID:19056867
        supporting_text: "Normal human urine contains large numbers of exosomes"
- term:
    id: GO:0005829
    label: cytosol
  evidence_type: TAS
  original_reference_id: Reactome:R-HSA-70577
  qualifier: located_in
  review:
    summary: >-
      Reactome traceable-author-statement localizing the ASS1 tetramer (in complex with NMRAL1
      dimer and NADPH) to the cytosol, in the argininosuccinate-forming reaction.
    action: ACCEPT
    reason: >-
      Consistent with the established cytosolic localization of ASS1; correct.
- term:
    id: GO:0005737
    label: cytoplasm
  evidence_type: TAS
  original_reference_id: PMID:6194510
  qualifier: located_in
  review:
    summary: >-
      Traceable author statement (from the human ASS cDNA sequencing paper) localizing ASS1 to the
      cytoplasm. This is the general parent of the more specific cytosol annotations.
    action: MODIFY
    reason: >-
      Correct but less specific than warranted: ASS1 is specifically cytosolic (GO:0005829), which
      is directly supported by immunofluorescence (IDA) and multiple sources. Replace the general
      "cytoplasm" with the more informative "cytosol".
    proposed_replacement_terms:
      - id: GO:0005829
        label: cytosol
core_functions:
- description: >-
    Argininosuccinate synthase: ATP-dependent condensation of L-citrulline and L-aspartate to form
    argininosuccinate (plus AMP and diphosphate) in the cytosol. This is the rate-limiting,
    committed step of de novo L-arginine biosynthesis and the argininosuccinate-forming step of the
    urea cycle, in which aspartate is the second nitrogen donor. The enzyme functions as a
    homotetramer of identical subunits, uses ATP as co-substrate (with defined ATP- and amino
    acid-binding sites), and its product is handed to argininosuccinate lyase (ASL) to yield
    arginine and fumarate.
  molecular_function:
    id: GO:0004055
    label: argininosuccinate synthase activity
  directly_involved_in:
    - id: GO:0000050
      label: urea cycle
    - id: GO:0006526
      label: L-arginine biosynthetic process
  locations:
    - id: GO:0005829
      label: cytosol
  substrates:
    - id: CHEBI:57743
      label: L-citrulline
    - id: CHEBI:29991
      label: L-aspartate
    - id: CHEBI:30616
      label: ATP
  supported_by:
    - reference_id: PMID:8792870
      supporting_text: "Argininosuccinate synthetase (ASS) is a urea cycle enzyme with a tetrameric"
    - reference_id: PMID:27287393
      supporting_text: "map near the substrate (aspartate or citrulline)"
    - reference_id: PMID:28985504
      supporting_text: "synthase (ASS1) to inactivate ASS1, which catalyzes the rate-limiting step of"
references:
- id: GO_REF:0000002
  title: Gene Ontology annotation through association of InterPro records with GO
    terms
  findings: []
- id: GO_REF:0000033
  title: Annotation inferences using phylogenetic trees
  findings: []
- id: GO_REF:0000044
  title: Gene Ontology annotation based on UniProtKB/Swiss-Prot Subcellular Location
    vocabulary mapping, accompanied by conservative changes to GO terms applied by
    UniProt
  findings: []
- id: GO_REF:0000052
  title: Gene Ontology annotation based on curation of immunofluorescence data
  findings: []
- id: GO_REF:0000107
  title: Automatic transfer of experimentally verified manual GO annotation data to
    orthologs using Ensembl Compara
  findings: []
- id: GO_REF:0000120
  title: Combined Automated Annotation using Multiple IEA Methods
  findings: []
- id: PMID:12620389
  title: Novel raf kinase protein-protein interactions found by an exhaustive yeast
    two-hybrid analysis.
  findings: []
  reference_review:
    relevance: LOW
    correctness: VERIFIED
    review_notes: >-
      High-throughput Y2H atlas of Raf-kinase interactors; ASS1/ARAF interaction is a screen hit
      with no established functional relevance to ASS1. Correctly cited for a binary interaction but
      only supports the uninformative "protein binding" term.
- id: PMID:16189514
  title: Towards a proteome-scale map of the human protein-protein interaction network.
  findings: []
  reference_review:
    relevance: MEDIUM
    correctness: VERIFIED
    review_notes: >-
      Interactome map reporting the ASS1 self-interaction, consistent with the known homotetramer.
- id: PMID:17496144
  title: Restructuring of the dinucleotide-binding fold in an NADP(H) sensor protein.
  findings: []
  reference_review:
    relevance: MEDIUM
    correctness: VERIFIED
    review_notes: >-
      Describes NMRAL1 (HSCARG) and notes it may regulate argininosuccinate synthetase; source of
      the ASS1-NMRAL1 interaction. Supports only the uninformative "protein binding" term.
- id: PMID:18473344
  title: Investigation of citrullinemia type I variants by in vitro expression studies.
  findings: []
  reference_review:
    relevance: HIGH
    correctness: VERIFIED
    review_notes: >-
      Bacterial expression/enzymology of wild-type and CTLN1 mutant ASS with measured KM and Vmax;
      directly supports argininosuccinate synthase activity, arginine biosynthesis, urea cycle, and
      the disease link. Basis for UniProt EC 6.3.4.5 and kinetic parameters.
- id: PMID:19056867
  title: Large-scale proteomics and phosphoproteomics of urinary exosomes.
  findings: []
  reference_review:
    relevance: LOW
    correctness: VERIFIED
    review_notes: >-
      Urinary exosome proteomics; ASS1 detected as an MS inventory hit, not evidence of functional
      exosomal localization for this cytosolic enzyme.
- id: PMID:21106532
  title: Endothelial argininosuccinate synthetase 1 regulates nitric oxide production
    and monocyte adhesion under static and laminar shear stress conditions.
  findings: []
  reference_review:
    relevance: HIGH
    correctness: VERIFIED
    review_notes: >-
      Endothelial cell study establishing the citrulline-NO cycle role of ASS1 (arginine supply for
      NOS3, effects on NO production and monocyte adhesion under shear stress). Supports the NO /
      shear-stress / adhesion BP annotations as non-core extrahepatic functions.
- id: PMID:21988832
  title: Toward an understanding of the protein interaction network of the human liver.
  findings: []
  reference_review:
    relevance: MEDIUM
    correctness: VERIFIED
    review_notes: >-
      Human liver interactome study reporting the ASS1 self-interaction, consistent with the
      homotetramer.
- id: PMID:22658674
  title: Insights into RNA biology from an atlas of mammalian mRNA-binding proteins.
  findings: []
  reference_review:
    relevance: LOW
    correctness: LOW_QUALITY
    review_notes: >-
      Single high-throughput mRNA-interactome-capture screen that recovered many metabolic enzymes,
      including ASS1, as putative RBPs. No orthogonal validation of an RNA-binding function for
      ASS1; basis for flagging the RNA binding annotation as over-annotated.
- id: PMID:23533145
  title: In-depth proteomic analyses of exosomes isolated from expressed prostatic
    secretions in urine.
  findings: []
  reference_review:
    relevance: LOW
    correctness: VERIFIED
    review_notes: >-
      Prostatic-secretion/urinary exosome proteomics; ASS1 detected as an MS inventory hit, not a
      functional localization.
- id: PMID:25416956
  title: A proteome-scale map of the human interactome network.
  findings: []
  reference_review:
    relevance: MEDIUM
    correctness: VERIFIED
    review_notes: >-
      Proteome-scale interactome map reporting the ASS1 self-interaction, consistent with the
      homotetramer.
- id: PMID:27287393
  title: 'Kinetic mutations in argininosuccinate synthetase deficiency: characterisation
    and in vitro correction by substrate supplementation.'
  findings: []
  reference_review:
    relevance: HIGH
    correctness: VERIFIED
    review_notes: >-
      Characterized 21 kinetic CTLN1 mutations by MS-based activity assays; 13 inactive, 8 with
      decreased aspartate/citrulline affinity rescuable by aspartate supplementation. Strong support
      for argininosuccinate synthase activity, substrate (amino acid) binding, and the urea
      cycle/arginine biosynthesis roles.
- id: PMID:28587924
  title: PRMT7 Interacts with ASS1 and Citrullinemia Mutations Disrupt the Interaction.
  findings: []
  reference_review:
    relevance: MEDIUM
    correctness: VERIFIED
    review_notes: >-
      Identifies and confirms (Y2H + pull-down) a direct PRMT7-ASS1 interaction disrupted by
      citrullinemia mutations. Genuine interaction but captured only as uninformative "protein
      binding".
- id: PMID:28985504
  title: CLOCK Acetylates ASS1 to Drive Circadian Rhythm of Ureagenesis.
  findings: []
  reference_review:
    relevance: HIGH
    correctness: VERIFIED
    review_notes: >-
      Shows CLOCK acetylates ASS1 K165/K176 to inactivate it in a circadian manner, driving a
      circadian rhythm of ureagenesis; also source of the direct cytosol localization and the
      ASS1-CLOCK interaction. Confirms ASS1 as the rate-limiting arginine-biosynthesis enzyme.
- id: PMID:6194510
  title: Sequence for human argininosuccinate synthetase cDNA.
  findings: []
  reference_review:
    relevance: MEDIUM
    correctness: VERIFIED
    review_notes: >-
      Early human ASS cDNA sequencing paper; cited (TAS) for cytoplasmic localization, generalized
      here to the more specific cytosol.
- id: PMID:7977368
  title: Mutations in argininosuccinate synthetase mRNA of Japanese patients, causing
    classical citrullinemia.
  findings: []
  reference_review:
    relevance: HIGH
    correctness: VERIFIED
    review_notes: >-
      Identifies ASS1 mutations causing classical citrullinemia; basis for the experimental urea
      cycle, argininosuccinate synthase activity, amino acid binding, and substrate
      (aspartate/citrulline) catabolic-process annotations.
- id: PMID:8792870
  title: Characterization of human wild-type and mutant argininosuccinate synthetase
    proteins expressed in bacterial cells.
  findings: []
  reference_review:
    relevance: HIGH
    correctness: VERIFIED
    review_notes: >-
      Recombinant human ASS enzymology; wild-type matched native liver enzyme, mutants showed
      reduced/abolished activity and abnormal kinetics. Explicitly describes ASS as a urea cycle
      enzyme with a tetrameric structure of identical subunits; supports catalytic activity, urea
      cycle, arginine biosynthesis, and the homotetramer.
- id: Reactome:R-HSA-70577
  title: ASS1 tetramer:NMRAL1 dimer:NADPH transforms L-Asp and L-Cit to ARSUA
  findings: []
- id: Reactome:R-HSA-9956517
  title: ASS1 variants don't synthesize arginosuccinate
  findings: []

ASS1

Gene Description

Existing Annotations Review

Core Functions

References

Deep Research

Falcon

Comprehensive Research Report: Human ASS1 (Argininosuccinate Synthase 1)

1. Gene and Protein Identity

2. Enzymatic Function: Reaction, Substrates, and Mechanism

2.1 Catalyzed Reaction

2.2 Catalytic Mechanism

3. Structural Biology

3.1 Domain Architecture

3.2 Quaternary Structure

4. Subcellular Localization

4.1 Cytosolic Localization

4.2 Nuclear Localization

5. Biological Pathways and Functions

5.1 Urea Cycle

5.2 De Novo Arginine Biosynthesis

5.3 Citrulline-NO Recycling Cycle

5.4 Aspartate Partitioning and Pyrimidine Metabolism

5.5 AMPK and Hepatic Lipid Metabolism

5.6 Nuclear DNA Damage Response

5.7 Circadian Regulation of Ureagenesis

6. Post-Translational Regulation

7. Disease Associations

7.1 Citrullinemia Type I (CTLN1)

7.2 Cancer and Arginine Auxotrophy

8. Summary

Artifacts

Citations

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