Existing Annotations Review

GO Term	Evidence	Action	Reason
GO:0004056 argininosuccinate lyase activity	IBA GO_REF:0000033	ACCEPT	Summary: Phylogenetically inferred core molecular function. ASL cleaves L-argininosuccinate to L-arginine and fumarate (EC 4.3.2.1), the reaction that defines this orthology group and is directly supported for the human enzyme by biochemical assay. Reason: This is the correct, well-supported core molecular function of ASL. The IBA is concordant with multiple human experimental annotations (EXP/IDA) and with the UniProt-curated catalytic activity. Supporting Evidence: PMID:11747433 Argininosuccinate lyase (ASL) is a homotetrameric enzyme that catalyzes the reversible cleavage of argininosuccinate to arginine and fumarate.
GO:0006526 L-arginine biosynthetic process	IBA GO_REF:0000033	ACCEPT	Summary: Phylogenetically inferred involvement in L-arginine biosynthesis. ASL performs the final (argininosuccinate-cleaving) step of de novo arginine synthesis from ornithine and carbamoyl phosphate. Reason: Correct core biological process, concordant with human IDA annotations and the UniProt-curated arginine-biosynthesis pathway (step 3/3). ASL supplies arginine both for the urea cycle in liver and for other arginine-dependent pathways in non-hepatic tissues. Supporting Evidence: PMID:11747432 a reaction involved in the biosynthesis of arginine in all species and in the production of urea in ureotelic species
GO:0005829 cytosol	IBA GO_REF:0000033	ACCEPT	Summary: Phylogenetically inferred cytosolic localization. ASL is a soluble cytosolic enzyme; its urea-cycle and arginine-biosynthesis reactions occur in the cytosol. Reason: Correct core cellular component, concordant with the human TAS cytosol/cytoplasm annotations and with the soluble, non-membrane biochemistry of the enzyme. Supporting Evidence: PMID:282632 ASL activity was visualized on gels after electrophoresis by a new method, termed bioautography
GO:0003824 catalytic activity	IEA GO_REF:0000002	MARK AS OVER ANNOTATED	Summary: Root-level catalytic activity assigned electronically from InterPro domain membership (fumarase/aspartase superfamily). This is the uninformative parent of the specific, correct term. Reason: ASL's molecular function is captured precisely and correctly by GO:0004056 argininosuccinate lyase activity (EC 4.3.2.1), which is annotated with strong experimental (EXP/IDA) and phylogenetic (IBA) support. GO:0003824 is the most general MF root and adds no information beyond "is an enzyme"; it should not be considered a core function statement.
GO:0004056 argininosuccinate lyase activity	IEA GO_REF:0000120	ACCEPT	Summary: Electronic assignment of argininosuccinate lyase activity from InterPro signature IPR009049, RHEA:24020 and EC 4.3.2.1. This is the correct core molecular function. Reason: Correct and specific molecular function, fully concordant with the human experimental and phylogenetic annotations to the same term.
GO:0006526 L-arginine biosynthetic process	IEA GO_REF:0000120	ACCEPT	Summary: Electronic assignment of L-arginine biosynthetic process from UniPathway mapping and ortholog evidence. Correct core process. Reason: Concordant with human IDA and IBA annotations to the same process; matches the UniProt-curated arginine biosynthesis pathway (step 3/3).
GO:0005515 protein binding	IPI PMID:25416956 A proteome-scale map of the human interactome network.	KEEP AS NON CORE	Summary: Generic protein binding recorded from a proteome-scale binary interactome (Y2H) screen (interactor NTAQ1, Q96HA8). The bare protein binding term is uninformative about ASL's molecular function. Reason: Per curation guidelines, bare GO:0005515 protein binding is not an informative molecular-function statement and is not a core function. The biologically meaningful self-association of ASL is captured by GO:0042802 (identical protein binding); the physiologically important heteromeric interactions (ASS1, SLC7A1, NOS) underlie the nitric-oxide role captured by GO:0045429. The interaction evidence itself is retained as non-core.
GO:0005515 protein binding	IPI PMID:26871637 Widespread Expansion of Protein Interaction Capabilities by ...	KEEP AS NON CORE	Summary: Generic protein binding from a high-throughput interactome study of alternative-splicing isoforms (interactor MCMBP isoform, Q9BTE3-2). Uninformative MF term. Reason: Bare protein binding is not an informative molecular function and is not core. The interaction detection is retained as non-core supporting data; the informative self-interaction is annotated separately as GO:0042802.
GO:0005515 protein binding	IPI PMID:31515488 Extensive disruption of protein interactions by genetic vari...	KEEP AS NON CORE	Summary: Generic protein binding from a large-scale study of interaction disruption by genetic variants (interactor NTAQ1, Q96HA8). Uninformative MF term. Reason: Bare protein binding is not an informative molecular function and is not core; retained as non-core interaction evidence.
GO:0005515 protein binding	IPI PMID:32296183 A reference map of the human binary protein interactome.	KEEP AS NON CORE	Summary: Generic protein binding from the HuRI reference binary interactome (multiple interactors, e.g. TRIM3 O75382, NTAQ1 Q96HA8, MCMBP Q9BTE3-2). Uninformative MF term. Reason: Bare protein binding is not an informative molecular function and is not core; retained as non-core interaction evidence. Physiologically relevant heteromeric partners (ASS1/SLC7A1/NOS) are not among these high-throughput hits.
GO:0042802 identical protein binding	IPI PMID:21988832 Toward an understanding of the protein interaction network o...	ACCEPT	Summary: ASL self-association (P04424-P04424) detected in a human liver protein interaction network study. This reflects the biologically real homotetramer. Reason: ASL is an obligate homotetramer whose subunits jointly form the shared active sites; self-association is intrinsic to its catalytic architecture and is directly supported by structural and biochemical work. This is an informative, correct molecular-function statement (unlike bare protein binding). Supporting Evidence: PMID:11747433 Argininosuccinate lyase (ASL) is a homotetrameric enzyme that catalyzes the reversible cleavage of argininosuccinate to arginine and fumarate.
GO:0042802 identical protein binding	IPI PMID:25416956 A proteome-scale map of the human interactome network.	ACCEPT	Summary: ASL self-association (P04424-P04424) detected in a proteome-scale binary interactome, consistent with the homotetramer. Reason: Corroborates the biologically real ASL homotetramer; informative and correct. Supporting Evidence: PMID:11747433 Argininosuccinate lyase (ASL) is a homotetrameric enzyme that catalyzes the reversible cleavage of argininosuccinate to arginine and fumarate.
GO:0042802 identical protein binding	IPI PMID:25502805 A massively parallel pipeline to clone DNA variants and exam...	ACCEPT	Summary: ASL self-association (P04424-P04424) detected in a massively parallel clone/variant interaction pipeline, consistent with the homotetramer. Reason: Corroborates the homotetramer; informative and correct self-interaction annotation. Supporting Evidence: PMID:11747433 Argininosuccinate lyase (ASL) is a homotetrameric enzyme that catalyzes the reversible cleavage of argininosuccinate to arginine and fumarate.
GO:0042802 identical protein binding	IPI PMID:31515488 Extensive disruption of protein interactions by genetic vari...	ACCEPT	Summary: ASL self-association (P04424-P04424) detected in a study of variant effects on protein interactions, consistent with the homotetramer. Reason: Corroborates the homotetramer; informative and correct self-interaction annotation. Supporting Evidence: PMID:11747433 Argininosuccinate lyase (ASL) is a homotetrameric enzyme that catalyzes the reversible cleavage of argininosuccinate to arginine and fumarate.
GO:0042802 identical protein binding	IPI PMID:32296183 A reference map of the human binary protein interactome.	ACCEPT	Summary: ASL self-association (P04424-P04424) detected in the HuRI reference binary interactome, consistent with the homotetramer. Reason: Corroborates the biologically real ASL homotetramer; informative and correct. Supporting Evidence: PMID:11747433 Argininosuccinate lyase (ASL) is a homotetrameric enzyme that catalyzes the reversible cleavage of argininosuccinate to arginine and fumarate.
GO:0045429 positive regulation of nitric oxide biosynthetic process	IEA GO_REF:0000107	KEEP AS NON CORE	Summary: Ensembl-Compara ortholog-transfer of a mouse Asl (Q91YI0) experimental annotation for the role of ASL in promoting nitric oxide biosynthesis. This transfers the same biology established experimentally for both mouse and human ASL in PMID:22081021. Reason: The underlying biology is genuine and experimentally supported in both species - ASL contributes, via a catalysis-independent structural role in the NOS multiprotein complex, to nitric oxide production. The orthology-transfer IEA is redundant with the human IMP annotation of the same term (PMID:22081021) but is not wrong. This is a secondary (moonlighting/structural) function rather than the enzyme's core catalytic function, hence non-core. Supporting Evidence: PMID:22081021 Mechanistic studies showed that ASL has a structural function in addition to its catalytic activity, by which it contributes to the formation of a multiprotein complex required for NO production.
GO:0000050 urea cycle	IEA GO_REF:0000041	ACCEPT	Summary: Electronic assignment of urea cycle from UniPathway mapping. ASL performs the step that regenerates arginine (from argininosuccinate) within the urea cycle, providing for hepatic nitrogen detoxification into urea. Reason: Correct core biological process. This is the canonical urea-cycle role of ASL and is central to the disease mechanism (hyperammonemia in argininosuccinic aciduria). Concordant with UniProt pathway curation (urea cycle, step 1/1 for this reaction). Supporting Evidence: PMID:11747432 a reaction involved in the biosynthesis of arginine in all species and in the production of urea in ureotelic species
GO:0005829 cytosol	TAS Reactome:R-HSA-9956524	ACCEPT	Summary: Reactome-asserted cytosolic localization (from the ASL variant urea-cycle reaction pathway). ASL is a soluble cytosolic enzyme. Reason: Correct core cellular component, concordant with the IBA and TAS cytosol/cytoplasm annotations.
GO:0004056 argininosuccinate lyase activity	EXP PMID:2263616 Molecular analysis of human argininosuccinate lyase: mutant ...	ACCEPT	Summary: Experimental demonstration of argininosuccinate lyase activity via characterization of human ASL and its ASA disease variants (e.g. R95C), including expression of mutant cDNA in COS cells showing loss of ASL activity. Reason: Direct experimental support for the core molecular function in the human enzyme. R95C produces little protein and less than 1% ASL activity, establishing that the assayed activity is that of the ASL gene product. Supporting Evidence: PMID:2263616 Expression in COS cells demonstrated that the R95C mutation produces normal amounts of ASAL mRNA but little protein and less than 1% ASAL activity.
GO:0004056 argininosuccinate lyase activity	IDA PMID:9045711 Intragenic complementation at the human argininosuccinate ly...	ACCEPT	Summary: Direct assay of ASL activity in COS-cell expression / intragenic complementation experiments, where the Q286R and D87G alleles each conferred loss of ASL activity and cotransfection partially restored it. Reason: Strong direct experimental support for the core catalytic function of human ASL. Supporting Evidence: PMID:9045711 each conferred loss of ASL activity in COS cell transfection assays
GO:0006525 arginine metabolic process	IDA PMID:9045711 Intragenic complementation at the human argininosuccinate ly...	KEEP AS NON CORE	Summary: Involvement in arginine metabolism inferred from direct assay of ASL activity and the resulting arginine production/loss in the complementation experiments. Reason: Correct but general. GO:0006525 arginine metabolic process is a broad parent; ASL's specific role is captured more precisely by GO:0006526 L-arginine biosynthetic process (the direction ASL contributes to). Retained as an accurate but non-core parent annotation. Supporting Evidence: PMID:9045711 each conferred loss of ASL activity in COS cell transfection assays
GO:0045429 positive regulation of nitric oxide biosynthetic process	IMP PMID:22081021 Requirement of argininosuccinate lyase for systemic nitric o...	KEEP AS NON CORE	Summary: Experimentally demonstrated requirement of ASL for nitric oxide production. Human ASA (ASL-null) subjects and cells, a hypomorphic Asl mouse, and ASL-knockdown cells all show reduced NOS-dependent NO. Crucially, catalytically dead but structurally intact human ASL mutants (R236W, R113Q) still support NOS complex formation and restore arginine-stimulated NO, showing this is a catalysis-independent structural role in assembling the NOS multiprotein complex (ASS1, SLC7A1, NOS). Reason: This is a genuine, well-supported second function of ASL (a moonlighting/structural role distinct from its catalytic activity) and explains the ammonia-independent systemic features (hypertension, hepatic/neurologic disease) of argininosuccinic aciduria. It is captured as a core function in core_functions as the NOS scaffold role, but relative to the enzyme's canonical urea-cycle/arginine-biosynthesis catalysis it is treated as non-core at the annotation level. Supporting Evidence: PMID:22081021 Mechanistic studies showed that ASL has a structural function in addition to its catalytic activity, by which it contributes to the formation of a multiprotein complex required for NO production. PMID:22081021 Loss of Asl in both humans and mice leads to reduced NO synthesis, owing to both decreased endogenous arginine synthesis and an impaired ability to use extracellular arginine for NO production.
GO:0004056 argininosuccinate lyase activity	IDA PMID:11747433 Mechanisms for intragenic complementation at the human argin...	ACCEPT	Summary: Direct biochemical characterization of recombinant human ASL and its active-site (Q286R, D87G) and stability (M360T, A398D) mutants, confirming argininosuccinate lyase activity and its dependence on the homotetrameric shared-active-site architecture. Reason: Strong direct experimental support for the core catalytic function; the paper reconstructs the reaction in vivo and in vitro with recombinant protein. Supporting Evidence: PMID:11747433 Argininosuccinate lyase (ASL) is a homotetrameric enzyme that catalyzes the reversible cleavage of argininosuccinate to arginine and fumarate.
GO:0006526 L-arginine biosynthetic process	IDA PMID:11747432 Three-dimensional structure of the argininosuccinate lyase f...	ACCEPT	Summary: The 2.65 A structure of the human ASL Q286R allele together with catalytic characterization supports ASL's role in the arginine-producing reaction of arginine biosynthesis. Reason: Correct core biological process, supported by direct structural/biochemical study of the human enzyme. The reaction is explicitly stated to be part of arginine biosynthesis. Supporting Evidence: PMID:11747432 a reaction involved in the biosynthesis of arginine in all species and in the production of urea in ureotelic species
GO:0006526 L-arginine biosynthetic process	IDA PMID:11747433 Mechanisms for intragenic complementation at the human argin...	ACCEPT	Summary: Biochemical reconstitution of the ASL reaction (argininosuccinate to arginine + fumarate) with recombinant human protein supports involvement in arginine biosynthesis. Reason: Correct core biological process, supported by direct assay of the arginine-producing reaction. Supporting Evidence: PMID:11747433 Argininosuccinate lyase (ASL) is a homotetrameric enzyme that catalyzes the reversible cleavage of argininosuccinate to arginine and fumarate.
GO:0004056 argininosuccinate lyase activity	IDA PMID:11747432 Three-dimensional structure of the argininosuccinate lyase f...	ACCEPT	Summary: Catalytic characterization and high-resolution structure of human ASL (Q286R allele) directly demonstrate argininosuccinate lyase activity and its kinetics (KM 0.12 mM for argininosuccinate). Reason: Strong direct experimental support for the core molecular function in the human enzyme. Supporting Evidence: PMID:11747432 Argininosuccinate lyase (ASL) catalyzes the reversible breakdown of argininosuccinate to arginine and fumarate
GO:0070062 extracellular exosome	HDA PMID:19056867 Large-scale proteomics and phosphoproteomics of urinary exos...	KEEP AS NON CORE	Summary: ASL peptides detected in urinary exosomes by large-scale proteomics/phosphoproteomics. This is a mass-spectrometry catalog location, not a site where ASL performs its known function. Reason: High-throughput proteomic detection in exosomes is common for abundant cytosolic enzymes and does not reflect a functional extracellular localization. ASL is a soluble cytosolic urea-cycle enzyme; the exosome finding is retained as non-core observational data. Cytosol (GO:0005829) is the functionally relevant compartment.
GO:0005829 cytosol	TAS Reactome:R-HSA-70573	ACCEPT	Summary: Reactome-asserted cytosolic localization (from the argininosuccinate to fumarate + arginine urea-cycle reaction). Correct. Reason: Correct core cellular component, concordant with the IBA and other TAS cytosol/cytoplasm annotations.
GO:0004056 argininosuccinate lyase activity	TAS PMID:282632 Argininosuccinic aciduria: assignment of the argininosuccina...	ACCEPT	Summary: Traceable assertion of ASL enzymatic activity (EC 4.3.2.1) from an early study that assayed human ASL by bioautography and mapped the ASL gene to chromosome 7. Reason: Correct core molecular function; the enzyme activity (EC 4.3.2.1) was directly detected and used to map the human gene. Supporting Evidence: PMID:282632 associated with a deficiency of argininosuccinate lyase (ASL; L-argininosuccinate arginine-lyase, EC 4.3.2.1)
GO:0005737 cytoplasm	TAS PMID:282632 Argininosuccinic aciduria: assignment of the argininosuccina...	ACCEPT	Summary: Traceable assertion of cytoplasmic localization for ASL. The more specific and functionally accurate term is cytosol (GO:0005829). Reason: Correct but general. Cytoplasm is accurate; the more specific cytosol term (annotated separately by IBA/TAS) is preferred as the core localization. Retained as an accurate broader-term annotation.
GO:0140378 protein complex scaffold activity	IMP PMID:22081021 Requirement of argininosuccinate lyase for systemic nitric o...	NEW	Summary: Proposed molecular-function statement for ASL's catalysis-independent structural role: it scaffolds a tissue-specific nitric oxide synthase multiprotein complex (with ASS1, SLC7A1 and NOS1/NOS2/NOS3). Catalytically dead but structurally intact human ASL (R236W, R113Q) still supports NOS complex formation, while loss of ASL disrupts the complex, defining a scaffold rather than catalytic function. Reason: GOA captures the downstream process (GO:0045429 positive regulation of nitric oxide biosynthetic process, IMP) but not the underlying molecular function. GO:0140378 protein complex scaffold activity best represents ASL's demonstrated role in holding the NOS complex together independently of its lyase catalysis, and grounds the corresponding core function. Supporting Evidence: PMID:22081021 Mechanistic studies showed that ASL has a structural function in addition to its catalytic activity, by which it contributes to the formation of a multiprotein complex required for NO production. file:human/ASL/ASL-deep-research-falcon.md forming a metabolon that channels arginine directly to NOS for nitric oxide (NO) production

Core Functions

Catalyzes the reversible cleavage of L-argininosuccinate to L-arginine and fumarate (EC 4.3.2.1), a step of the cytosolic urea cycle, as an obligate homotetramer with shared active sites.

Molecular Function:

argininosuccinate lyase activity

Directly Involved In:

urea cycle

Cellular Locations:

cytosol

Supporting Evidence:

PMID:11747433
Argininosuccinate lyase (ASL) is a homotetrameric enzyme that catalyzes the reversible cleavage of argininosuccinate to arginine and fumarate.
PMID:282632
associated with a deficiency of argininosuccinate lyase (ASL; L-argininosuccinate arginine-lyase, EC 4.3.2.1)

Regenerates L-arginine from argininosuccinate as the final step of de novo arginine biosynthesis, supplying arginine for downstream pathways in hepatic and non-hepatic tissues.

Molecular Function:

argininosuccinate lyase activity

Directly Involved In:

L-arginine biosynthetic process

Cellular Locations:

cytosol

Supporting Evidence:

PMID:11747432
a reaction involved in the biosynthesis of arginine in all species and in the production of urea in ureotelic species

Provides a catalysis-independent scaffold function that holds together a tissue-specific nitric oxide synthase multiprotein complex (with ASS1, SLC7A1 and NOS1/NOS2/NOS3), channelling arginine to nitric oxide production and thereby positively regulating nitric oxide biosynthesis.

Molecular Function:

protein complex scaffold activity

Directly Involved In:

positive regulation of nitric oxide biosynthetic process

Cellular Locations:

cytosol

Supporting Evidence:

PMID:22081021
Mechanistic studies showed that ASL has a structural function in addition to its catalytic activity, by which it contributes to the formation of a multiprotein complex required for NO production.

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:0000041

Gene Ontology annotation based on UniPathway vocabulary mapping

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:11747432

Three-dimensional structure of the argininosuccinate lyase frequently complementing allele Q286R.

PMID:11747433

Mechanisms for intragenic complementation at the human argininosuccinate lyase locus.

PMID:19056867

Large-scale proteomics and phosphoproteomics of urinary exosomes.

PMID:21988832

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

PMID:22081021

Requirement of argininosuccinate lyase for systemic nitric oxide production.

PMID:2263616

Molecular analysis of human argininosuccinate lyase: mutant characterization and alternative splicing of the coding region.

PMID:25416956

A proteome-scale map of the human interactome network.

PMID:25502805

A massively parallel pipeline to clone DNA variants and examine molecular phenotypes of human disease mutations.

PMID:26871637

Widespread Expansion of Protein Interaction Capabilities by Alternative Splicing.

PMID:282632

Argininosuccinic aciduria: assignment of the argininosuccinate lyase gene to the pter to q22 region of human chromosome 7 by bioautography.

PMID:31515488

Extensive disruption of protein interactions by genetic variants across the allele frequency spectrum in human populations.

PMID:32296183

A reference map of the human binary protein interactome.

PMID:9045711

Intragenic complementation at the human argininosuccinate lyase locus. Identification of the major complementing alleles.

Reactome:R-HSA-70573

argininosuccinate <=> fumarate + arginine

Reactome:R-HSA-9956524

ASL variants don't synthesize fumarate and arginine

file:human/ASL/ASL-deep-research-falcon.md

Deep research report (falcon) for human ASL

Deep Research

Falcon

(ASL-deep-research-falcon.md)

Comprehensive Functional Annotation of Human ASL (Argininosuccinate Lyase) Falcon Edison Scientific Literature 40 citations 1 artifacts 2026-07-05T13:25:20.571681

Edison artifact artifact-00 (text/markdown)

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We are specifically interested in the primary function of the gene - for enzymes, what reaction is catalyzed, and what is the substrate specificity? For transporters, what is the substrate? For structural proteins or adapters, what is the broader structural role? For signaling molecules, what is the role in the pathway.

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Include evidence where possible. We are interested in both experimental evidence as well as inference from structure, evolution, or bioinformatic analysis. Precise studies should be prioritized over high-throughput, where available.

Comprehensive Functional Annotation of Human ASL (Argininosuccinate Lyase)

Gene and Protein Identity

The human ASL gene (UniProt: P04424) encodes argininosuccinate lyase (ASAL; EC 4.3.2.1), also known as arginosuccinase. The gene is located on chromosome 7 (7q11.21), spanning approximately 17,554 base pairs organized into 16 coding exons plus an exon 0 that encodes only the 5′ untranslated region (baruteau2019argininosuccinicaciduriarecent pages 1-6, erez2011argininosuccinatelyasedeficiency—argininosuccinic pages 4-5, baruteau2019argininosuccinicaciduriarecent pages 6-9). The encoded protein consists of 464 amino acids with a monomer molecular weight of approximately 52 kDa (nagamani2012argininosuccinatelyasedeficiency pages 2-3). ASL belongs to the lyase 1 family and is a member of the β-elimination/fumarate lyase superfamily, sharing structural homology with fumarase, aspartase, and adenylosuccinate lyase (chakraborty1999mutationalanalysisof pages 48-53, toth2000thestructureof pages 1-2).

The following table summarizes the key molecular and functional properties of human ASL:

Property	Summary
Gene name	ASL (argininosuccinate lyase; argininosuccinase) in Homo sapiens (human) (baruteau2019argininosuccinicaciduriarecent pages 1-6, erez2011argininosuccinatelyasedeficiency—argininosuccinic pages 4-5)
UniProt accession	P04424
Chromosome location	Chromosome 7; reported as 7q11.21 / cen-q11.2, with gene structure including exon 0 for 5' UTR and 16 coding exons (baruteau2019argininosuccinicaciduriarecent pages 1-6, erez2011argininosuccinatelyasedeficiency—argininosuccinic pages 4-5, baruteau2019argininosuccinicaciduriarecent pages 6-9)
Protein size	464 aa, about 52 kDa per monomer (tetramer ~208 kDa) (nagamani2012argininosuccinatelyasedeficiency pages 2-3)
Quaternary structure	Homotetramer with 4 active sites; each active site is formed at the interface of three subunits (chakraborty1999mutationalanalysisof pages 48-53, baruteau2019argininosuccinicaciduriarecent pages 1-6, nagamani2012argininosuccinatelyasedeficiency pages 2-3)
EC number	EC 4.3.2.1 (argininosuccinate lyase) (baruteau2019argininosuccinicaciduriarecent pages 1-6)
Reaction catalyzed	Reversible cleavage of argininosuccinate → L-arginine + fumarate; this is the 4th step of the urea cycle and also supplies arginine in the citrulline-NO cycle (chakraborty1999mutationalanalysisof pages 36-42, baruteau2019argininosuccinicaciduriarecent pages 1-6, wu1998argininemetabolismnitric pages 2-3)
Substrate specificity	Physiologic substrate is argininosuccinic acid (argininosuccinate); ASL is the only enzyme capable of generating endogenous arginine in mammalian cells (nagamani2012argininosuccinatelyasedeficiency pages 2-3, keshet2018arginineandthe pages 2-2)
Catalytic mechanism	β-elimination (ElcB) mechanism with a carbanion intermediate; elimination proceeds with trans stereochemistry, and C–N bond cleavage is likely rate-limiting (chakraborty1999mutationalanalysisof pages 36-42, chakraborty1999mutationalanalysisof pages 42-48)
Subcellular localization	Cytosolic enzyme; also functions in a compartmentalized CAT1-ASS1-ASL-NOS complex for arginine channeling to NOS (baruteau2019argininosuccinicaciduriarecent pages 1-6, baruteau2019argininosuccinicaciduriarecent pages 6-9, mori2004argininemetabolicenzymes pages 2-3)
Primary tissue expression	Expressed predominantly in liver; also present in kidney (proximal tubules), brain, heart, muscle, skin, hematopoietic tissues, small intestine, pancreas, fibroblasts, and erythrocytes. Kidney is a major site of endogenous arginine synthesis (~60% net synthesis in adults) (baruteau2019argininosuccinicaciduriarecent pages 1-6, nagamani2012argininosuccinatelyasedeficiency pages 2-3, chakraborty1999mutationalanalysisof pages 36-42)
Pathway involvement	Urea cycle: supports ammonia detoxification/ureagenesis. Citrulline-NO cycle: regenerates arginine from citrulline to support nitric oxide synthesis by NOS (baruteau2019argininosuccinicaciduriarecent pages 1-6, mori2004argininemetabolicenzymes pages 1-2)
Superfamily / family membership	Member of the β-elimination / fumarate-lyase-related superfamily, related to δ-crystallin, fumarase, aspartase, and adenylosuccinate lyase; highly conserved across bacteria to mammals (chakraborty1999mutationalanalysisof pages 48-53, erez2011argininosuccinatelyasedeficiency—argininosuccinic pages 4-5, toth2000thestructureof pages 1-2)
Key catalytic residues	Frequently implicated catalytic residues include H91, H162, K289, E296; H162/K289/E296 are central to proton abstraction and charge-relay chemistry (chakraborty1999mutationalanalysisof pages 42-48, chakraborty1999mutationalanalysisof pages 48-53)
Disease association	Biallelic pathogenic variants cause ASL deficiency (ASLD), also called argininosuccinic aciduria (ASA), a urea-cycle disorder with hyperammonemia and broader systemic disease including neurocognitive and liver manifestations (baruteau2019argininosuccinicaciduriarecent pages 1-6, gurung2024mrnatherapycorrects pages 11-12, kho2023argininosuccinatelyasedeficiency pages 4-6)

Table: This table summarizes the core molecular, structural, biochemical, and disease-related properties of human argininosuccinate lyase (ASL). It is useful as a compact reference for functional annotation and for connecting ASL’s enzymatic role to its pathway context and disease relevance.

1. Enzymatic Function: Reaction and Substrate Specificity

ASL catalyzes the reversible cleavage of L-argininosuccinate into L-arginine and fumarate (chakraborty1999mutationalanalysisof pages 36-42, baruteau2019argininosuccinicaciduriarecent pages 1-6, wu1998argininemetabolismnitric pages 2-3). This reaction represents the fourth step of the urea cycle and is the sole enzymatic means of generating endogenous arginine in mammalian cells (nagamani2012argininosuccinatelyasedeficiency pages 2-3, keshet2018arginineandthe pages 2-2). The physiological substrate is argininosuccinic acid (argininosuccinate), and the products are L-arginine and fumarate (nagamani2012argininosuccinatelyasedeficiency pages 2-3). Kinetic studies using the homologous duck δ II crystallin (which retains ASL activity) have reported a V_max of 3.47 μmol/min/mg protein and a K_m of 0.35 mM (chakraborty1999mutationalanalysisof pages 32-36). In bovine and human ASL, non-linear kinetics with negative cooperativity at high substrate concentrations have been observed, with potential allosteric regulation by GTP (chakraborty1999mutationalanalysisof pages 42-48).

The reaction proceeds via an E1cB (elimination, unimolecular, conjugate base) mechanism involving a carbanion intermediate (chakraborty1999mutationalanalysisof pages 36-42, chakraborty1999mutationalanalysisof pages 42-48). Catalysis is initiated by proton abstraction at the Cβ position of argininosuccinate, generating a carbanion intermediate, followed by proton donation at the guanidinium nitrogen concurrent with cleavage of the Cα–N bond. The elimination proceeds with trans stereochemistry, requiring five atoms (catalytic base, H, Cβ, Cα, and N) to be coplanar. C–N bond cleavage is the likely rate-limiting step, and fumarate release exceeds arginine release by an order of magnitude (chakraborty1999mutationalanalysisof pages 36-42, chakraborty1999mutationalanalysisof pages 42-48).

2. Protein Structure and Catalytic Architecture

ASL functions as a cytosolic homotetramer with a total molecular weight of approximately 208 kDa, containing four catalytically active sites (chakraborty1999mutationalanalysisof pages 48-53, baruteau2019argininosuccinicaciduriarecent pages 1-6, nagamani2012argininosuccinatelyasedeficiency pages 2-3). Each monomer adopts a predominantly α-helical fold organized into three domains. The active sites are formed at the interfaces of three different subunits within the tetramer, meaning that proper quaternary assembly is essential for enzymatic activity (chakraborty1999mutationalanalysisof pages 48-53, nagamani2012argininosuccinatelyasedeficiency pages 2-3). This multi-subunit active site architecture also underpins the phenomenon of intragenic complementation, whereby heterotetramers formed from two individually inactive mutant monomers can regain partial enzymatic function (baruteau2019argininosuccinicaciduriarecent pages 6-9, engel2012bacterialexpressionof pages 7-8).

Key catalytic residues include His162, which acts as the general base for proton abstraction; Lys289, which is absolutely conserved and stabilizes the carbanion intermediate; Glu296, which participates in a charge-relay network with His162 to enhance its basicity; and His91, which plays a role in substrate binding and catalysis (chakraborty1999mutationalanalysisof pages 42-48, chakraborty1999mutationalanalysisof pages 48-53). These residues are spatially distributed across different monomers but cluster together at the active site upon tetramer formation. Despite low overall sequence identity (approximately 15%) among superfamily members, three highly conserved regions that contribute these catalytic residues are maintained across all members of the fumarate lyase superfamily (chakraborty1999mutationalanalysisof pages 48-53).

3. Subcellular Localization and Tissue Distribution

ASL is a cytosolic enzyme (baruteau2019argininosuccinicaciduriarecent pages 1-6, chakraborty1999mutationalanalysisof pages 36-42, wu1998argininemetabolismnitric pages 2-3). It is predominantly expressed in the liver, where it functions as part of the hepatic urea cycle localized in periportal hepatocytes (baruteau2019argininosuccinicaciduriarecent pages 1-6, wu1998argininemetabolismnitric pages 5-6). However, ASL expression is ubiquitous and is also found at significant levels in the kidney (specifically in proximal tubules, where approximately 60% of net endogenous arginine synthesis occurs in adult mammals), brain, heart, skeletal muscle, skin, hematopoietic tissues, small intestine, pancreas, fibroblasts, and erythrocytes (baruteau2019argininosuccinicaciduriarecent pages 1-6, nagamani2012argininosuccinatelyasedeficiency pages 2-3, erez2011argininosuccinatelyasedeficiency—argininosuccinic pages 3-4, chakraborty1999mutationalanalysisof pages 36-42).

Importantly, ASL is not only a soluble cytoplasmic enzyme but also participates in a multiprotein complex at specific subcellular locations. In endothelial cells, ASL has been shown to colocalize with the cationic amino acid transporter CAT1, argininosuccinate synthase (ASS1), and endothelial nitric oxide synthase (eNOS) in caveolae, forming a metabolon that channels arginine directly to NOS for nitric oxide (NO) production (baruteau2019argininosuccinicaciduriarecent pages 6-9, mori2004argininemetabolicenzymes pages 2-3). This compartmentalized complex is critical for efficient NO biosynthesis and has functional significance beyond what bulk arginine availability alone would predict.

4. Biochemical and Signaling Pathways

4.1 The Urea Cycle

ASL catalyzes the fourth of five enzymatic steps in the urea cycle, which is the primary pathway for detoxification of ammonia in mammals (baruteau2019argininosuccinicaciduriarecent pages 1-6). In this pathway, ammonia derived from amino acid catabolism is converted to urea through the sequential actions of carbamoyl phosphate synthetase I (CPS1), ornithine transcarbamylase (OTC), argininosuccinate synthase (ASS1), ASL, and arginase 1 (ARG1). The first two steps occur in the mitochondrial matrix, while ASS1, ASL, and ARG1 operate in the cytosol. ASL cleaves argininosuccinate to produce arginine, which is then hydrolyzed by arginase to yield urea and ornithine, completing the cycle. The fumarate released by ASL can enter the TCA cycle as an anaplerotic substrate (wu1998argininemetabolismnitric pages 2-3).

4.2 The Citrulline-NO Cycle

Beyond its role in ureagenesis, ASL functions as a critical component of the citrulline-NO cycle (also called the arginine-citrulline cycle), which supports nitric oxide synthesis (baruteau2019argininosuccinicaciduriarecent pages 1-6, mori2004argininemetabolicenzymes pages 1-2, mori2004argininemetabolicenzymes pages 2-3, keshet2018arginineandthe pages 2-2). In this pathway, ASS1 condenses citrulline (a byproduct of NOS activity) with aspartate to form argininosuccinate, which ASL then cleaves to regenerate arginine. Arginine is subsequently used by NOS to produce NO and citrulline, completing the cycle. This recycling mechanism is essential for sustained NO production in cells expressing all three NOS isoforms (neuronal nNOS, endothelial eNOS, and inducible iNOS) (mori2004argininemetabolicenzymes pages 1-2).

The citrulline-NO cycle has been demonstrated to be functional in multiple cell types, including activated macrophages, microglia, glial cells, neuronal PC12 cells, retinal pigment epithelial cells, and vascular endothelial cells (mori2004argininemetabolicenzymes pages 1-2). ASL and ASS are coinduced with iNOS during inflammatory stimulation in macrophages, and colocalize with both nNOS and eNOS in neurons and endothelial cells, respectively (mori2004argininemetabolicenzymes pages 2-3). The colocalization of ASL with eNOS in endothelial caveolae, as part of a multiprotein complex including CAT1 and ASS1, facilitates efficient arginine channeling that is essential for regulated NO production (baruteau2019argininosuccinicaciduriarecent pages 6-9, mori2004argininemetabolicenzymes pages 2-3).

4.3 Arginine as a Metabolic Nexus

Because ASL is the only enzyme in mammalian cells capable of generating endogenous arginine de novo, its product serves as a precursor for multiple biologically important pathways, including the synthesis of urea, NO, polyamines, proline, glutamate, creatine, and agmatine (nagamani2012argininosuccinatelyasedeficiency pages 2-3, erez2011argininosuccinatelyasedeficiency—argininosuccinic pages 3-4, keshet2018arginineandthe pages 2-2). This positions ASL at a critical metabolic nexus linking nitrogen disposal, signaling, protein synthesis, and energy metabolism.

5. Evolutionary Conservation and Relationship to δ-Crystallin

ASL is highly evolutionarily conserved across species ranging from bacteria and yeast to plants and mammals (erez2011argininosuccinatelyasedeficiency—argininosuccinic pages 4-5, baruteau2019argininosuccinicaciduriarecent pages 6-9). Human and yeast ASL sequences share approximately 50% nucleotide identity and 54% amino acid identity (chakraborty1999mutationalanalysisof pages 36-42). Notably, ASL shares a common ancestral origin with avian δ-crystallins, which were recruited from an ancestral ASL gene to serve structural roles in the lens of birds and reptiles (erez2011argininosuccinatelyasedeficiency—argininosuccinic pages 4-5, chakraborty1999mutationalanalysisof pages 32-36). Of the two avian δ-crystallin isoforms (δI and δII), which share approximately 89% amino acid sequence identity, only δII retains catalytic ASL activity with kinetic parameters comparable to mammalian ASL, while δI has been specialized for a purely structural role (chakraborty1999mutationalanalysisof pages 32-36). This represents a classic example of gene sharing, where a single gene serves both enzymatic and structural functions. The conservation of ASL in birds, which lack a functional urea cycle, further demonstrates that ASL's role in arginine generation for protein synthesis and NO production is evolutionarily fundamental, independent of ureagenesis (erez2011argininosuccinatelyasedeficiency—argininosuccinic pages 4-5). Fifteen of the intron/exon boundaries are in identical positions between the rat ASL gene and chicken δ-crystallin genes, providing strong structural evidence for their shared origin (chakraborty1999mutationalanalysisof pages 32-36).

6. ASL Deficiency and Disease

6.1 Argininosuccinic Aciduria (ASA)

Biallelic pathogenic variants in ASL cause argininosuccinate lyase deficiency (ASLD; OMIM 207900), also known as argininosuccinic aciduria (ASA), an autosomal recessive urea cycle disorder (baruteau2019argininosuccinicaciduriarecent pages 1-6, kho2023argininosuccinatelyasedeficiency pages 1-2). ASLD presents as a spectrum of disease ranging from severe neonatal-onset hyperammonemia to late-onset and even asymptomatic forms. Approximately 140 pathogenic variants have been documented in the ASL gene, including missense, nonsense, insertion, deletion, and splicing mutations, with exons 4, 5, and 7 identified as mutational hotspots (erez2011argininosuccinatelyasedeficiency—argininosuccinic pages 4-5, baruteau2019argininosuccinicaciduriarecent pages 6-9). Three founder mutations have been identified in Saudi Arabian and Finnish populations (baruteau2019argininosuccinicaciduriarecent pages 6-9). A notable feature of ASLD is the phenomenon of intragenic complementation, whereby compound heterozygous patients may have milder phenotypes than expected from individual allelic effects, owing to the multi-subunit active site architecture (baruteau2019argininosuccinicaciduriarecent pages 6-9, engel2012bacterialexpressionof pages 7-8).

6.2 Beyond Hyperammonemia: NO Deficiency and Systemic Disease

A critical insight from recent research is that ASLD is not merely a disorder of ammonia detoxification but a systemic disease with neurocognitive, hepatic, and vascular manifestations that can occur independently of hyperammonemia (baruteau2019argininosuccinicaciduriarecent pages 1-6, kho2023argininosuccinatelyasedeficiency pages 1-2). This is attributable to ASL's role in the citrulline-NO cycle: loss of ASL leads to cell-autonomous NO deficiency because arginine cannot be regenerated intracellularly for NOS, even when extracellular arginine is available (kho2023argininosuccinatelyasedeficiency pages 4-6, kho2023argininosuccinatelyasedeficiency pages 6-7, kho2023argininosuccinatelyasedeficiency pages 2-4). A landmark study by Kho et al. (2023) demonstrated that ASL deficiency disrupts blood-brain barrier (BBB) integrity through NO-mediated dysregulation of tight junction claudin proteins, specifically causing upregulation of claudin-1 and downregulation of claudin-5 in brain microvascular endothelial cells (kho2023argininosuccinatelyasedeficiency pages 4-6, kho2023argininosuccinatelyasedeficiency pages 2-4, kho2023argininosuccinatelyasedeficiency pages 7-9). In vivo, hypomorphic ASL-deficient mice showed BBB leakage that was partially rescued by NO supplementation with sodium nitrite, establishing a direct mechanistic link between ASL-dependent NO production and BBB maintenance (kho2023argininosuccinatelyasedeficiency pages 6-7, kho2023argininosuccinatelyasedeficiency pages 9-10).

Additionally, Gurung et al. (2024) identified dysregulation of glutathione biosynthesis and oxidative stress as a novel pathophysiological mechanism in ASLD, with upregulated cysteine metabolism contrasting with glutathione depletion and downregulated antioxidant pathways in both patients and animal models (gurung2024mrnatherapycorrects pages 11-12, gurung2024mrnatherapycorrects pages 1-3).

6.3 Emerging Therapeutic Approaches

Several novel therapeutic strategies for ASLD are under active development:

mRNA Therapy: Gurung et al. (2024) demonstrated that human ASL mRNA encapsulated in lipid nanoparticles (LNP) corrected glutathione metabolism, improved chronic liver disease, and restored ureagenesis in ASL-deficient mouse models. Treatment from birth normalized plasma metabolites and liver ASL expression. The study also introduced [18F]FSPG PET as a noninvasive tool to monitor disease and therapeutic response (gurung2024mrnatherapycorrects pages 11-12, gurung2024mrnatherapycorrects pages 1-3). Independently, Daly et al. (2023) showed that nucleoside-modified ASL mRNA-LNP provided complete survival protection in ASL-deficient mice at 3 mg/kg administered twice weekly, with a favorable safety and immunogenicity profile (daly2023aslmrnalnptherapeutic pages 1-2, daly2023aslmrnalnptherapeutic pages 11-13).

CRISPR Base Editing: Jalil et al. (2024) demonstrated that CRISPR adenine base editors (ABE8e) delivered via lipid nanoparticles could correct the common c.1153C>T pathogenic variant in patient-derived primary fibroblasts, restoring ASL enzyme activity to approximately 59% of healthy donor levels and significantly reducing argininosuccinic acid accumulation (jalil2024geneticandfunctional pages 11-12).

These therapeutic advances underscore the dual enzymatic and structural roles of ASL—liver-directed therapies can address ureagenesis and hepatic disease, but the systemic NO-related manifestations, particularly neurological complications, remain a challenge that may require complementary approaches (daly2023aslmrnalnptherapeutic pages 13-15).

7. Summary

Human ASL (P04424) is a cytosolic homotetrameric enzyme that catalyzes the reversible β-elimination of argininosuccinate to yield arginine and fumarate via an E1cB mechanism with a carbanion intermediate. It operates at the intersection of two critical metabolic pathways—the urea cycle for ammonia detoxification and the citrulline-NO cycle for nitric oxide synthesis—and is the sole enzyme capable of endogenous arginine generation. ASL is expressed broadly across tissues, with highest levels in liver and kidney. Its participation in a multiprotein complex with ASS1 and NOS enables arginine channeling for regulated NO production in endothelial and other cell types. ASL is highly conserved from bacteria to mammals and shares evolutionary and structural origins with avian δ-crystallins. Loss-of-function mutations cause argininosuccinic aciduria, a systemic disorder with hyperammonemia, NO deficiency, glutathione dysregulation, and neurovascular complications including blood-brain barrier disruption. Recent therapeutic advances including mRNA-LNP and CRISPR base editing approaches show significant preclinical promise for correcting ASL deficiency.

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Artifacts

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Citations

nagamani2012argininosuccinatelyasedeficiency pages 2-3
baruteau2019argininosuccinicaciduriarecent pages 1-6
chakraborty1999mutationalanalysisof pages 32-36
chakraborty1999mutationalanalysisof pages 42-48
chakraborty1999mutationalanalysisof pages 48-53
wu1998argininemetabolismnitric pages 2-3
mori2004argininemetabolicenzymes pages 1-2
mori2004argininemetabolicenzymes pages 2-3
chakraborty1999mutationalanalysisof pages 36-42
baruteau2019argininosuccinicaciduriarecent pages 6-9
jalil2024geneticandfunctional pages 11-12
daly2023aslmrnalnptherapeutic pages 13-15
toth2000thestructureof pages 1-2
keshet2018arginineandthe pages 2-2
gurung2024mrnatherapycorrects pages 11-12
kho2023argininosuccinatelyasedeficiency pages 4-6
engel2012bacterialexpressionof pages 7-8
wu1998argininemetabolismnitric pages 5-6
kho2023argininosuccinatelyasedeficiency pages 1-2
kho2023argininosuccinatelyasedeficiency pages 6-7
kho2023argininosuccinatelyasedeficiency pages 2-4
kho2023argininosuccinatelyasedeficiency pages 7-9
kho2023argininosuccinatelyasedeficiency pages 9-10
gurung2024mrnatherapycorrects pages 1-3
daly2023aslmrnalnptherapeutic pages 1-2
daly2023aslmrnalnptherapeutic pages 11-13
18F
https://doi.org/10.1002/jimd.12047,
https://doi.org/10.1002/ajmg.c.30289,
https://doi.org/10.1038/gim.2011.1,
https://doi.org/10.1021/bi982150g,
https://doi.org/10.1016/s0969-2126(00
https://doi.org/10.1042/bj3360001,
https://doi.org/10.1242/dmm.033332,
https://doi.org/10.1093/jn/134.10.2820s,
https://doi.org/10.1126/scitranslmed.adh1334,
https://doi.org/10.1172/jci.insight.168475,
https://doi.org/10.1007/s10545-011-9357-x,
https://doi.org/10.3390/biomedicines11061735,
https://doi.org/10.1016/j.ajhg.2024.03.004,

📚 Additional Documentation

Notes

(ASL-notes.md)

ASL (argininosuccinate lyase, P04424) — review notes

Core enzyme function

ASL catalyzes the reversible cleavage of L-argininosuccinate to L-arginine + fumarate (EC 4.3.2.1;
RHEA:24020). It is the third/final step of the L-arginine biosynthesis branch and the second-to-last
step of the urea cycle (cytosolic).

UniProt P04424 FUNCTION: "Catalyzes the reversible cleavage of L-argininosuccinate to fumarate and
L-arginine, an intermediate step reaction in the urea cycle mostly providing for hepatic nitrogen
detoxification into excretable urea as well as de novo L-arginine synthesis in nonhepatic tissues"
(ECO:0000269 from PubMed:11747432, 11747433, 22081021, 2263616, 9045711).
EC 4.3.2.1 established by direct enzyme assay in humans, e.g. PMID:282632.
Homotetramer: PMID:11747433; first
high-resolution human structure is the Q286R allele PMID:11747432. Active sites are shared between tetramer subunits,
the basis of the well-documented intragenic complementation in ASA patients.
Lyase 1 family, argininosuccinate lyase subfamily; fumarase/aspartase (L-aspartase-like) superfamily
(UniProt SIMILARITY + InterPro IPR008948 L-Aspartase-like, IPR000362 Fumarate_lyase_fam).

Second, non-catalytic (structural) role: nitric oxide production

ASL has a well-documented structural role in assembling a NOS-containing multiprotein complex that
channels arginine to nitric oxide synthase; this is independent of catalytic activity.

PMID:22081021
Human catalytic-dead mutants retain the structural function: R236W "abolishes the enzymatic
activity ... but does not abolish its tertiary structure"; overexpressing R113Q (catalytically dead)
in ASA fibroblasts restored arginine-stimulated nitrite (NO) production. Loss of ASL, not loss of
its catalysis, disrupts the NOS complex.
Human ASA subjects show loss of NOS-dependent (flow-mediated) vascular relaxation but normal
response to a NOS-independent NO donor (nitroglycerin), and reduced plasma RSNO/nitrite despite
high plasma arginine — a systemic NO deficiency phenotype distinct from hyperammonemia.
UniProt SUBUNIT: "Forms tissue-specific complexes with ASS1, SLC7A1, HSP90AA1 and nitric oxide
synthase NOS1, NOS2 or NOS3; the complex maintenance is independent of ASL catalytic function"
(partly By similarity to mouse Q91YI0).
GOA term used is GO:0045429 "positive regulation of nitric oxide biosynthetic process" (IMP,
PMID:22081021, human ASL) and an Ensembl-Compara ortholog-transfer IEA (GO_REF:0000107) of the
same term from mouse Asl (Q91YI0). Both point to the same real biology.

Disease

Argininosuccinic aciduria (ASA / ASLD; MIM 207900; MONDO:0008815), autosomal recessive, second most
common urea cycle disorder (~1 in 70,000; dismech kb/disorders/Argininosuccinic_Aciduria.yaml). Beyond
hyperammonemia, chronic ammonia-independent complications (neurocognitive, hepatic fibrosis, systemic
hypertension) are attributed in part to cell-autonomous NO deficiency (PMID:22081021).

Localization

Cytosolic enzyme (GO:0005829). UniProt DR: cytosol IBA (GO_Central), cytoplasm TAS (ProtInc,
PMID:282632). Also detected in urinary exosomes by large-scale proteomics PMID:19056867 — a
mass-spec location catalog finding, not a curated site of action.

Annotation decisions summary

Core: GO:0004056 (MF, EXP/IDA/IBA), GO:0000050 urea cycle (BP), GO:0006526 L-arginine biosynthetic
process (BP), GO:0005829 cytosol (CC), GO:0042802 identical protein binding (homotetramer).
Second core / non-core: GO:0045429 positive regulation of NO biosynthetic process (structural NOS
role, PMID:22081021).
MARK_AS_OVER_ANNOTATED: GO:0003824 catalytic activity (root MF, InterPro IEA) — too general; a
specific EC 4.3.2.1 term (GO:0004056) is annotated.
Bare GO:0005515 protein binding IPI (from high-throughput interactome/Y2H/AP-MS screens): not
informative MF; the biologically meaningful self-association is captured by GO:0042802. Keep as
non-core (evidence exists) but not core.
GO:0070062 extracellular exosome (HDA, urinary exosome proteomics) — mass-spec catalog location,
keep as non-core.
GO:0006525 arginine metabolic process (IDA) — correct but general parent of the more specific
GO:0006526; keep as non-core.

📄 View Raw YAML

id: P04424
gene_symbol: ASL
product_type: PROTEIN
status: INITIALIZED
taxon:
  id: NCBITaxon:9606
  label: Homo sapiens
description: >-
  Argininosuccinate lyase (ASL; arginosuccinase; EC 4.3.2.1) is a cytosolic enzyme
  that catalyzes the reversible cleavage of L-argininosuccinate into L-arginine and
  fumarate. This reaction is the third and final step of L-arginine biosynthesis and
  a step of the urea cycle, in which ASL acts downstream of argininosuccinate synthase
  (ASS1) to regenerate arginine; in hepatocytes arginine is then hydrolyzed by arginase
  to release urea for nitrogen detoxification, while in non-hepatic tissues ASL provides
  arginine for other pathways. ASL is a homotetramer belonging to the lyase 1 family
  (argininosuccinate lyase subfamily) within the fumarase/aspartase (L-aspartase-like)
  superfamily; its four active sites are each built from residues contributed by more
  than one subunit, which is the structural basis for the extensive intragenic (interallelic)
  complementation seen among disease alleles. Beyond its catalytic role, ASL has a
  distinct, catalysis-independent structural function: it is required to assemble and
  maintain a tissue-specific multiprotein complex (with argininosuccinate synthase,
  the arginine transporter SLC7A1/CAT-1, HSP90 and a nitric oxide synthase NOS1/NOS2/NOS3)
  that channels intracellular and extracellular arginine to nitric oxide synthesis.
  Loss of ASL function causes argininosuccinic aciduria, an autosomal recessive urea
  cycle disorder featuring hyperammonemia together with ammonia-independent systemic
  features (systemic hypertension, chronic hepatic disease, neurocognitive impairment)
  attributable in part to cell-autonomous nitric oxide deficiency.
alternative_products:
- name: '1'
  id: P04424-1
- name: '2'
  id: P04424-2
  sequence_note: VSP_047256
- name: '3'
  id: P04424-3
  sequence_note: VSP_047255
existing_annotations:
- term:
    id: GO:0004056
    label: argininosuccinate lyase activity
  evidence_type: IBA
  original_reference_id: GO_REF:0000033
  qualifier: enables
  review:
    summary: >-
      Phylogenetically inferred core molecular function. ASL cleaves L-argininosuccinate
      to L-arginine and fumarate (EC 4.3.2.1), the reaction that defines this orthology
      group and is directly supported for the human enzyme by biochemical assay.
    action: ACCEPT
    reason: >-
      This is the correct, well-supported core molecular function of ASL. The IBA
      is concordant with multiple human experimental annotations (EXP/IDA) and with
      the UniProt-curated catalytic activity.
    supported_by:
    - reference_id: PMID:11747433
      supporting_text: Argininosuccinate lyase (ASL) is a homotetrameric enzyme that
        catalyzes the reversible cleavage of argininosuccinate to arginine and fumarate.
- 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 involvement in L-arginine biosynthesis. ASL performs
      the final (argininosuccinate-cleaving) step of de novo arginine synthesis from
      ornithine and carbamoyl phosphate.
    action: ACCEPT
    reason: >-
      Correct core biological process, concordant with human IDA annotations and the
      UniProt-curated arginine-biosynthesis pathway (step 3/3). ASL supplies arginine
      both for the urea cycle in liver and for other arginine-dependent pathways in
      non-hepatic tissues.
    supported_by:
    - reference_id: PMID:11747432
      supporting_text: a reaction involved in the biosynthesis of arginine in all
        species and in the production of urea in ureotelic species
- 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. ASL is a soluble cytosolic
      enzyme; its urea-cycle and arginine-biosynthesis reactions occur in the cytosol.
    action: ACCEPT
    reason: >-
      Correct core cellular component, concordant with the human TAS cytosol/cytoplasm
      annotations and with the soluble, non-membrane biochemistry of the enzyme.
    supported_by:
    - reference_id: PMID:282632
      supporting_text: ASL activity was visualized on gels after electrophoresis by
        a new method, termed bioautography
- term:
    id: GO:0003824
    label: catalytic activity
  evidence_type: IEA
  original_reference_id: GO_REF:0000002
  qualifier: enables
  review:
    summary: >-
      Root-level catalytic activity assigned electronically from InterPro domain membership
      (fumarase/aspartase superfamily). This is the uninformative parent of the specific,
      correct term.
    action: MARK_AS_OVER_ANNOTATED
    reason: >-
      ASL's molecular function is captured precisely and correctly by GO:0004056 argininosuccinate
      lyase activity (EC 4.3.2.1), which is annotated with strong experimental (EXP/IDA)
      and phylogenetic (IBA) support. GO:0003824 is the most general MF root and adds
      no information beyond "is an enzyme"; it should not be considered a core function
      statement.
- term:
    id: GO:0004056
    label: argininosuccinate lyase activity
  evidence_type: IEA
  original_reference_id: GO_REF:0000120
  qualifier: enables
  review:
    summary: >-
      Electronic assignment of argininosuccinate lyase activity from InterPro signature
      IPR009049, RHEA:24020 and EC 4.3.2.1. This is the correct core molecular function.
    action: ACCEPT
    reason: >-
      Correct and specific molecular function, fully concordant with the human experimental
      and phylogenetic annotations to the same term.
- term:
    id: GO:0006526
    label: L-arginine biosynthetic process
  evidence_type: IEA
  original_reference_id: GO_REF:0000120
  qualifier: involved_in
  review:
    summary: >-
      Electronic assignment of L-arginine biosynthetic process from UniPathway mapping
      and ortholog evidence. Correct core process.
    action: ACCEPT
    reason: >-
      Concordant with human IDA and IBA annotations to the same process; matches the
      UniProt-curated arginine biosynthesis pathway (step 3/3).
- term:
    id: GO:0005515
    label: protein binding
  evidence_type: IPI
  original_reference_id: PMID:25416956
  qualifier: enables
  review:
    summary: >-
      Generic protein binding recorded from a proteome-scale binary interactome (Y2H)
      screen (interactor NTAQ1, Q96HA8). The bare protein binding term is uninformative
      about ASL's molecular function.
    action: KEEP_AS_NON_CORE
    reason: >-
      Per curation guidelines, bare GO:0005515 protein binding is not an informative
      molecular-function statement and is not a core function. The biologically meaningful
      self-association of ASL is captured by GO:0042802 (identical protein binding);
      the physiologically important heteromeric interactions (ASS1, SLC7A1, NOS) underlie
      the nitric-oxide role captured by GO:0045429. The interaction evidence itself
      is retained as non-core.
- term:
    id: GO:0005515
    label: protein binding
  evidence_type: IPI
  original_reference_id: PMID:26871637
  qualifier: enables
  review:
    summary: >-
      Generic protein binding from a high-throughput interactome study of alternative-splicing
      isoforms (interactor MCMBP isoform, Q9BTE3-2). Uninformative MF term.
    action: KEEP_AS_NON_CORE
    reason: >-
      Bare protein binding is not an informative molecular function and is not core.
      The interaction detection is retained as non-core supporting data; the informative
      self-interaction is annotated separately as GO:0042802.
- term:
    id: GO:0005515
    label: protein binding
  evidence_type: IPI
  original_reference_id: PMID:31515488
  qualifier: enables
  review:
    summary: >-
      Generic protein binding from a large-scale study of interaction disruption by
      genetic variants (interactor NTAQ1, Q96HA8). Uninformative MF term.
    action: KEEP_AS_NON_CORE
    reason: >-
      Bare protein binding is not an informative molecular function and is not core;
      retained as non-core interaction evidence.
- term:
    id: GO:0005515
    label: protein binding
  evidence_type: IPI
  original_reference_id: PMID:32296183
  qualifier: enables
  review:
    summary: >-
      Generic protein binding from the HuRI reference binary interactome (multiple
      interactors, e.g. TRIM3 O75382, NTAQ1 Q96HA8, MCMBP Q9BTE3-2). Uninformative
      MF term.
    action: KEEP_AS_NON_CORE
    reason: >-
      Bare protein binding is not an informative molecular function and is not core;
      retained as non-core interaction evidence. Physiologically relevant heteromeric
      partners (ASS1/SLC7A1/NOS) are not among these high-throughput hits.
- term:
    id: GO:0042802
    label: identical protein binding
  evidence_type: IPI
  original_reference_id: PMID:21988832
  qualifier: enables
  review:
    summary: >-
      ASL self-association (P04424-P04424) detected in a human liver protein interaction
      network study. This reflects the biologically real homotetramer.
    action: ACCEPT
    reason: >-
      ASL is an obligate homotetramer whose subunits jointly form the shared active
      sites; self-association is intrinsic to its catalytic architecture and is directly
      supported by structural and biochemical work. This is an informative, correct
      molecular-function statement (unlike bare protein binding).
    supported_by:
    - reference_id: PMID:11747433
      supporting_text: Argininosuccinate lyase (ASL) is a homotetrameric enzyme that
        catalyzes the reversible cleavage of argininosuccinate to arginine and fumarate.
- term:
    id: GO:0042802
    label: identical protein binding
  evidence_type: IPI
  original_reference_id: PMID:25416956
  qualifier: enables
  review:
    summary: >-
      ASL self-association (P04424-P04424) detected in a proteome-scale binary interactome,
      consistent with the homotetramer.
    action: ACCEPT
    reason: Corroborates the biologically real ASL homotetramer; informative and correct.
    supported_by:
    - reference_id: PMID:11747433
      supporting_text: Argininosuccinate lyase (ASL) is a homotetrameric enzyme that
        catalyzes the reversible cleavage of argininosuccinate to arginine and fumarate.
- term:
    id: GO:0042802
    label: identical protein binding
  evidence_type: IPI
  original_reference_id: PMID:25502805
  qualifier: enables
  review:
    summary: >-
      ASL self-association (P04424-P04424) detected in a massively parallel clone/variant
      interaction pipeline, consistent with the homotetramer.
    action: ACCEPT
    reason: Corroborates the homotetramer; informative and correct self-interaction
      annotation.
    supported_by:
    - reference_id: PMID:11747433
      supporting_text: Argininosuccinate lyase (ASL) is a homotetrameric enzyme that
        catalyzes the reversible cleavage of argininosuccinate to arginine and fumarate.
- term:
    id: GO:0042802
    label: identical protein binding
  evidence_type: IPI
  original_reference_id: PMID:31515488
  qualifier: enables
  review:
    summary: >-
      ASL self-association (P04424-P04424) detected in a study of variant effects
      on protein interactions, consistent with the homotetramer.
    action: ACCEPT
    reason: Corroborates the homotetramer; informative and correct self-interaction
      annotation.
    supported_by:
    - reference_id: PMID:11747433
      supporting_text: Argininosuccinate lyase (ASL) is a homotetrameric enzyme that
        catalyzes the reversible cleavage of argininosuccinate to arginine and fumarate.
- term:
    id: GO:0042802
    label: identical protein binding
  evidence_type: IPI
  original_reference_id: PMID:32296183
  qualifier: enables
  review:
    summary: >-
      ASL self-association (P04424-P04424) detected in the HuRI reference binary interactome,
      consistent with the homotetramer.
    action: ACCEPT
    reason: Corroborates the biologically real ASL homotetramer; informative and correct.
    supported_by:
    - reference_id: PMID:11747433
      supporting_text: Argininosuccinate lyase (ASL) is a homotetrameric enzyme that
        catalyzes the reversible cleavage of argininosuccinate to arginine and fumarate.
- term:
    id: GO:0045429
    label: positive regulation of nitric oxide biosynthetic process
  evidence_type: IEA
  original_reference_id: GO_REF:0000107
  qualifier: involved_in
  review:
    summary: >-
      Ensembl-Compara ortholog-transfer of a mouse Asl (Q91YI0) experimental annotation
      for the role of ASL in promoting nitric oxide biosynthesis. This transfers the
      same biology established experimentally for both mouse and human ASL in PMID:22081021.
    action: KEEP_AS_NON_CORE
    reason: >-
      The underlying biology is genuine and experimentally supported in both species
      - ASL contributes, via a catalysis-independent structural role in the NOS multiprotein
      complex, to nitric oxide production. The orthology-transfer IEA is redundant
      with the human IMP annotation of the same term (PMID:22081021) but is not wrong.
      This is a secondary (moonlighting/structural) function rather than the enzyme's
      core catalytic function, hence non-core.
    supported_by:
    - reference_id: PMID:22081021
      supporting_text: Mechanistic studies showed that ASL has a structural function
        in addition to its catalytic activity, by which it contributes to the formation
        of a multiprotein complex required for NO production.
- term:
    id: GO:0000050
    label: urea cycle
  evidence_type: IEA
  original_reference_id: GO_REF:0000041
  qualifier: involved_in
  review:
    summary: >-
      Electronic assignment of urea cycle from UniPathway mapping. ASL performs the
      step that regenerates arginine (from argininosuccinate) within the urea cycle,
      providing for hepatic nitrogen detoxification into urea.
    action: ACCEPT
    reason: >-
      Correct core biological process. This is the canonical urea-cycle role of ASL
      and is central to the disease mechanism (hyperammonemia in argininosuccinic
      aciduria). Concordant with UniProt pathway curation (urea cycle, step 1/1 for
      this reaction).
    supported_by:
    - reference_id: PMID:11747432
      supporting_text: a reaction involved in the biosynthesis of arginine in all
        species and in the production of urea in ureotelic species
- term:
    id: GO:0005829
    label: cytosol
  evidence_type: TAS
  original_reference_id: Reactome:R-HSA-9956524
  qualifier: located_in
  review:
    summary: >-
      Reactome-asserted cytosolic localization (from the ASL variant urea-cycle reaction
      pathway). ASL is a soluble cytosolic enzyme.
    action: ACCEPT
    reason: >-
      Correct core cellular component, concordant with the IBA and TAS cytosol/cytoplasm
      annotations.
- term:
    id: GO:0004056
    label: argininosuccinate lyase activity
  evidence_type: EXP
  original_reference_id: PMID:2263616
  qualifier: enables
  review:
    summary: >-
      Experimental demonstration of argininosuccinate lyase activity via characterization
      of human ASL and its ASA disease variants (e.g. R95C), including expression
      of mutant cDNA in COS cells showing loss of ASL activity.
    action: ACCEPT
    reason: >-
      Direct experimental support for the core molecular function in the human enzyme.
      R95C produces little protein and less than 1% ASL activity, establishing that
      the assayed activity is that of the ASL gene product.
    supported_by:
    - reference_id: PMID:2263616
      supporting_text: Expression in COS cells demonstrated that the R95C mutation
        produces normal amounts of ASAL mRNA but little protein and less than 1% ASAL
        activity.
- term:
    id: GO:0004056
    label: argininosuccinate lyase activity
  evidence_type: IDA
  original_reference_id: PMID:9045711
  qualifier: enables
  review:
    summary: >-
      Direct assay of ASL activity in COS-cell expression / intragenic complementation
      experiments, where the Q286R and D87G alleles each conferred loss of ASL activity
      and cotransfection partially restored it.
    action: ACCEPT
    reason: Strong direct experimental support for the core catalytic function of
      human ASL.
    supported_by:
    - reference_id: PMID:9045711
      supporting_text: each conferred loss of ASL activity in COS cell transfection
        assays
- term:
    id: GO:0006525
    label: arginine metabolic process
  evidence_type: IDA
  original_reference_id: PMID:9045711
  qualifier: involved_in
  review:
    summary: >-
      Involvement in arginine metabolism inferred from direct assay of ASL activity
      and the resulting arginine production/loss in the complementation experiments.
    action: KEEP_AS_NON_CORE
    reason: >-
      Correct but general. GO:0006525 arginine metabolic process is a broad parent;
      ASL's specific role is captured more precisely by GO:0006526 L-arginine biosynthetic
      process (the direction ASL contributes to). Retained as an accurate but non-core
      parent annotation.
    supported_by:
    - reference_id: PMID:9045711
      supporting_text: each conferred loss of ASL activity in COS cell transfection
        assays
- term:
    id: GO:0045429
    label: positive regulation of nitric oxide biosynthetic process
  evidence_type: IMP
  original_reference_id: PMID:22081021
  qualifier: involved_in
  review:
    summary: >-
      Experimentally demonstrated requirement of ASL for nitric oxide production.
      Human ASA (ASL-null) subjects and cells, a hypomorphic Asl mouse, and ASL-knockdown
      cells all show reduced NOS-dependent NO. Crucially, catalytically dead but structurally
      intact human ASL mutants (R236W, R113Q) still support NOS complex formation
      and restore arginine-stimulated NO, showing this is a catalysis-independent structural
      role in assembling the NOS multiprotein complex (ASS1, SLC7A1, NOS).
    action: KEEP_AS_NON_CORE
    reason: >-
      This is a genuine, well-supported second function of ASL (a moonlighting/structural
      role distinct from its catalytic activity) and explains the ammonia-independent
      systemic features (hypertension, hepatic/neurologic disease) of argininosuccinic
      aciduria. It is captured as a core function in core_functions as the NOS scaffold
      role, but relative to the enzyme's canonical urea-cycle/arginine-biosynthesis
      catalysis it is treated as non-core at the annotation level.
    supported_by:
    - reference_id: PMID:22081021
      supporting_text: Mechanistic studies showed that ASL has a structural function
        in addition to its catalytic activity, by which it contributes to the formation
        of a multiprotein complex required for NO production.
    - reference_id: PMID:22081021
      supporting_text: Loss of Asl in both humans and mice leads to reduced NO synthesis,
        owing to both decreased endogenous arginine synthesis and an impaired ability
        to use extracellular arginine for NO production.
- term:
    id: GO:0004056
    label: argininosuccinate lyase activity
  evidence_type: IDA
  original_reference_id: PMID:11747433
  qualifier: enables
  review:
    summary: >-
      Direct biochemical characterization of recombinant human ASL and its active-site
      (Q286R, D87G) and stability (M360T, A398D) mutants, confirming argininosuccinate
      lyase activity and its dependence on the homotetrameric shared-active-site architecture.
    action: ACCEPT
    reason: >-
      Strong direct experimental support for the core catalytic function; the paper
      reconstructs the reaction in vivo and in vitro with recombinant protein.
    supported_by:
    - reference_id: PMID:11747433
      supporting_text: Argininosuccinate lyase (ASL) is a homotetrameric enzyme that
        catalyzes the reversible cleavage of argininosuccinate to arginine and fumarate.
- term:
    id: GO:0006526
    label: L-arginine biosynthetic process
  evidence_type: IDA
  original_reference_id: PMID:11747432
  qualifier: involved_in
  review:
    summary: >-
      The 2.65 A structure of the human ASL Q286R allele together with catalytic characterization
      supports ASL's role in the arginine-producing reaction of arginine biosynthesis.
    action: ACCEPT
    reason: >-
      Correct core biological process, supported by direct structural/biochemical
      study of the human enzyme. The reaction is explicitly stated to be part of arginine
      biosynthesis.
    supported_by:
    - reference_id: PMID:11747432
      supporting_text: a reaction involved in the biosynthesis of arginine in all
        species and in the production of urea in ureotelic species
- term:
    id: GO:0006526
    label: L-arginine biosynthetic process
  evidence_type: IDA
  original_reference_id: PMID:11747433
  qualifier: involved_in
  review:
    summary: >-
      Biochemical reconstitution of the ASL reaction (argininosuccinate to arginine
      + fumarate) with recombinant human protein supports involvement in arginine
      biosynthesis.
    action: ACCEPT
    reason: >-
      Correct core biological process, supported by direct assay of the arginine-producing
      reaction.
    supported_by:
    - reference_id: PMID:11747433
      supporting_text: Argininosuccinate lyase (ASL) is a homotetrameric enzyme that
        catalyzes the reversible cleavage of argininosuccinate to arginine and fumarate.
- term:
    id: GO:0004056
    label: argininosuccinate lyase activity
  evidence_type: IDA
  original_reference_id: PMID:11747432
  qualifier: enables
  review:
    summary: >-
      Catalytic characterization and high-resolution structure of human ASL (Q286R
      allele) directly demonstrate argininosuccinate lyase activity and its kinetics
      (KM 0.12 mM for argininosuccinate).
    action: ACCEPT
    reason: Strong direct experimental support for the core molecular function in
      the human enzyme.
    supported_by:
    - reference_id: PMID:11747432
      supporting_text: Argininosuccinate lyase (ASL) catalyzes the reversible breakdown
        of argininosuccinate to arginine and fumarate
- term:
    id: GO:0070062
    label: extracellular exosome
  evidence_type: HDA
  original_reference_id: PMID:19056867
  qualifier: located_in
  review:
    summary: >-
      ASL peptides detected in urinary exosomes by large-scale proteomics/phosphoproteomics.
      This is a mass-spectrometry catalog location, not a site where ASL performs
      its known function.
    action: KEEP_AS_NON_CORE
    reason: >-
      High-throughput proteomic detection in exosomes is common for abundant cytosolic
      enzymes and does not reflect a functional extracellular localization. ASL is
      a soluble cytosolic urea-cycle enzyme; the exosome finding is retained as non-core
      observational data. Cytosol (GO:0005829) is the functionally relevant compartment.
- term:
    id: GO:0005829
    label: cytosol
  evidence_type: TAS
  original_reference_id: Reactome:R-HSA-70573
  qualifier: located_in
  review:
    summary: >-
      Reactome-asserted cytosolic localization (from the argininosuccinate to fumarate
      + arginine urea-cycle reaction). Correct.
    action: ACCEPT
    reason: >-
      Correct core cellular component, concordant with the IBA and other TAS cytosol/cytoplasm
      annotations.
- term:
    id: GO:0004056
    label: argininosuccinate lyase activity
  evidence_type: TAS
  original_reference_id: PMID:282632
  qualifier: enables
  review:
    summary: >-
      Traceable assertion of ASL enzymatic activity (EC 4.3.2.1) from an early study
      that assayed human ASL by bioautography and mapped the ASL gene to chromosome
      7.
    action: ACCEPT
    reason: >-
      Correct core molecular function; the enzyme activity (EC 4.3.2.1) was directly
      detected and used to map the human gene.
    supported_by:
    - reference_id: PMID:282632
      supporting_text: associated with a deficiency of argininosuccinate lyase (ASL;
        L-argininosuccinate arginine-lyase, EC 4.3.2.1)
- term:
    id: GO:0005737
    label: cytoplasm
  evidence_type: TAS
  original_reference_id: PMID:282632
  qualifier: located_in
  review:
    summary: >-
      Traceable assertion of cytoplasmic localization for ASL. The more specific and
      functionally accurate term is cytosol (GO:0005829).
    action: ACCEPT
    reason: >-
      Correct but general. Cytoplasm is accurate; the more specific cytosol term (annotated
      separately by IBA/TAS) is preferred as the core localization. Retained as an
      accurate broader-term annotation.
- term:
    id: GO:0140378
    label: protein complex scaffold activity
  evidence_type: IMP
  original_reference_id: PMID:22081021
  qualifier: enables
  review:
    summary: >-
      Proposed molecular-function statement for ASL's catalysis-independent structural
      role: it scaffolds a tissue-specific nitric oxide synthase multiprotein complex
      (with ASS1, SLC7A1 and NOS1/NOS2/NOS3). Catalytically dead but structurally intact
      human ASL (R236W, R113Q) still supports NOS complex formation, while loss of
      ASL disrupts the complex, defining a scaffold rather than catalytic function.
    action: NEW
    reason: >-
      GOA captures the downstream process (GO:0045429 positive regulation of nitric
      oxide biosynthetic process, IMP) but not the underlying molecular function.
      GO:0140378 protein complex scaffold activity best represents ASL's demonstrated
      role in holding the NOS complex together independently of its lyase catalysis,
      and grounds the corresponding core function.
    additional_reference_ids:
    - file:human/ASL/ASL-deep-research-falcon.md
    supported_by:
    - reference_id: PMID:22081021
      supporting_text: Mechanistic studies showed that ASL has a structural function
        in addition to its catalytic activity, by which it contributes to the formation
        of a multiprotein complex required for NO production.
    - reference_id: file:human/ASL/ASL-deep-research-falcon.md
      supporting_text: forming a metabolon that channels arginine directly to NOS
        for nitric oxide (NO) production
core_functions:
- description: >-
    Catalyzes the reversible cleavage of L-argininosuccinate to L-arginine and fumarate
    (EC 4.3.2.1), a step of the cytosolic urea cycle, as an obligate homotetramer
    with shared active sites.
  molecular_function:
    id: GO:0004056
    label: argininosuccinate lyase activity
  directly_involved_in:
  - id: GO:0000050
    label: urea cycle
  locations:
  - id: GO:0005829
    label: cytosol
  supported_by:
  - reference_id: PMID:11747433
    supporting_text: Argininosuccinate lyase (ASL) is a homotetrameric enzyme that
      catalyzes the reversible cleavage of argininosuccinate to arginine and fumarate.
  - reference_id: PMID:282632
    supporting_text: associated with a deficiency of argininosuccinate lyase (ASL;
      L-argininosuccinate arginine-lyase, EC 4.3.2.1)
- description: >-
    Regenerates L-arginine from argininosuccinate as the final step of de novo arginine
    biosynthesis, supplying arginine for downstream pathways in hepatic and non-hepatic
    tissues.
  molecular_function:
    id: GO:0004056
    label: argininosuccinate lyase activity
  directly_involved_in:
  - id: GO:0006526
    label: L-arginine biosynthetic process
  locations:
  - id: GO:0005829
    label: cytosol
  supported_by:
  - reference_id: PMID:11747432
    supporting_text: a reaction involved in the biosynthesis of arginine in all species
      and in the production of urea in ureotelic species
- description: >-
    Provides a catalysis-independent scaffold function that holds together a tissue-specific
    nitric oxide synthase multiprotein complex (with ASS1, SLC7A1 and NOS1/NOS2/NOS3),
    channelling arginine to nitric oxide production and thereby positively regulating
    nitric oxide biosynthesis.
  molecular_function:
    id: GO:0140378
    label: protein complex scaffold activity
  directly_involved_in:
  - id: GO:0045429
    label: positive regulation of nitric oxide biosynthetic process
  locations:
  - id: GO:0005829
    label: cytosol
  supported_by:
  - reference_id: PMID:22081021
    supporting_text: Mechanistic studies showed that ASL has a structural function
      in addition to its catalytic activity, by which it contributes to the formation
      of a multiprotein complex required for NO production.
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:0000041
  title: Gene Ontology annotation based on UniPathway vocabulary mapping
  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:11747432
  title: Three-dimensional structure of the argininosuccinate lyase frequently complementing
    allele Q286R.
  findings: []
  reference_review:
    relevance: HIGH
    correctness: VERIFIED
    review_notes: >-
      PubMed-verified. First high-resolution (2.65 A) structure of human ASL (Q286R
      allele); establishes catalytic activity, kinetics, and homotetrameric architecture.
      Abstract-only in cache but concordant with UniProt curation.
- id: PMID:11747433
  title: Mechanisms for intragenic complementation at the human argininosuccinate
    lyase locus.
  findings: []
  reference_review:
    relevance: HIGH
    correctness: VERIFIED
    review_notes: >-
      PubMed-verified. Defines ASL as a homotetramer catalyzing reversible cleavage
      of argininosuccinate to arginine and fumarate; reconstructs intragenic complementation
      in vitro and in vivo. Abstract-only in cache.
- id: PMID:19056867
  title: Large-scale proteomics and phosphoproteomics of urinary exosomes.
  findings: []
  reference_review:
    relevance: LOW
    correctness: VERIFIED
    review_notes: >-
      High-throughput proteomic detection of ASL in urinary exosomes; a catalog location,
      not evidence of functional extracellular localization.
- 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: >-
      Detects ASL self-interaction (P04424-P04424), consistent with the known homotetramer.
- id: PMID:22081021
  title: Requirement of argininosuccinate lyase for systemic nitric oxide production.
  findings: []
  reference_review:
    relevance: HIGH
    correctness: VERIFIED
    review_notes: >-
      Full text in cache (PMC3348956). Demonstrates a catalysis-independent structural
      role of ASL in NOS multiprotein complex assembly and NO production in both mouse
      and human (including human ASA subjects and catalytically dead R236W/R113Q human
      ASL). Basis for the GO:0045429 IMP and the Ensembl-Compara IEA.
- id: PMID:2263616
  title: 'Molecular analysis of human argininosuccinate lyase: mutant characterization
    and alternative splicing of the coding region.'
  findings: []
  reference_review:
    relevance: HIGH
    correctness: VERIFIED
    review_notes: >-
      PubMed-verified. Establishes that ASA deficiency maps to the ASL structural
      gene; R95C expressed in COS cells gives less than 1% ASL activity. Supports
      core catalytic function. Abstract-only in cache.
- id: PMID:25416956
  title: A proteome-scale map of the human interactome network.
  findings: []
  reference_review:
    relevance: MEDIUM
    correctness: VERIFIED
    review_notes: >-
      Proteome-scale binary interactome; source of an ASL self-interaction (GO:0042802)
      and a generic protein-binding (GO:0005515) annotation.
- id: PMID:25502805
  title: A massively parallel pipeline to clone DNA variants and examine molecular
    phenotypes of human disease mutations.
  findings: []
  reference_review:
    relevance: MEDIUM
    correctness: VERIFIED
    review_notes: >-
      High-throughput clone/variant interaction pipeline; source of an ASL self-interaction
      (GO:0042802) annotation.
- id: PMID:26871637
  title: Widespread Expansion of Protein Interaction Capabilities by Alternative Splicing.
  findings: []
  reference_review:
    relevance: LOW
    correctness: VERIFIED
    review_notes: >-
      High-throughput isoform interactome; source of a generic protein-binding (GO:0005515)
      annotation with an MCMBP isoform.
- id: PMID:282632
  title: 'Argininosuccinic aciduria: assignment of the argininosuccinate lyase gene
    to the pter to q22 region of human chromosome 7 by bioautography.'
  findings: []
  reference_review:
    relevance: MEDIUM
    correctness: VERIFIED
    review_notes: >-
      PubMed-verified. Detects human ASL activity (EC 4.3.2.1) by bioautography and
      maps the ASL gene to chromosome 7. Supports catalytic activity and cytoplasmic
      localization (TAS). Abstract-only in cache.
- id: PMID:31515488
  title: Extensive disruption of protein interactions by genetic variants across the
    allele frequency spectrum in human populations.
  findings: []
  reference_review:
    relevance: LOW
    correctness: VERIFIED
    review_notes: >-
      Large-scale variant interaction study; source of ASL self-interaction (GO:0042802)
      and generic protein-binding (GO:0005515) annotations.
- id: PMID:32296183
  title: A reference map of the human binary protein interactome.
  findings: []
  reference_review:
    relevance: MEDIUM
    correctness: VERIFIED
    review_notes: >-
      HuRI reference interactome; source of an ASL self-interaction (GO:0042802) and
      generic protein-binding (GO:0005515) annotations.
- id: PMID:9045711
  title: Intragenic complementation at the human argininosuccinate lyase locus. Identification
    of the major complementing alleles.
  findings: []
  reference_review:
    relevance: HIGH
    correctness: VERIFIED
    review_notes: >-
      PubMed-verified. Direct COS-cell assay of human ASL activity; Q286R and D87G
      alleles confer loss of activity and cotransfection partially restores it (proof
      of intragenic complementation). Supports core catalytic function and arginine
      metabolism. Abstract-only in cache.
- id: Reactome:R-HSA-70573
  title: argininosuccinate <=> fumarate + arginine
  findings: []
- id: Reactome:R-HSA-9956524
  title: ASL variants don't synthesize fumarate and arginine
  findings: []
- id: file:human/ASL/ASL-deep-research-falcon.md
  title: Deep research report (falcon) for human ASL
  findings: []
  reference_review:
    relevance: MEDIUM
    correctness: VERIFIED
    review_notes: >-
      LLM-generated deep-research synthesis. Corroborates the cytosolic homotetramer,
      the argininosuccinate to arginine + fumarate reaction, urea-cycle and citrulline-NO-cycle
      roles, and the CAT1-ASS1-ASL-NOS metabolon. Only used here for the well-established
      NOS-metabolon claim, which is independently confirmed by PMID:22081021.

ASL

Gene Description

Existing Annotations Review

Core Functions

Catalyzes the reversible cleavage of L-argininosuccinate to L-arginine and fumarate (EC 4.3.2.1), a step of the cytosolic urea cycle, as an obligate homotetramer with shared active sites.

Regenerates L-arginine from argininosuccinate as the final step of de novo arginine biosynthesis, supplying arginine for downstream pathways in hepatic and non-hepatic tissues.

Provides a catalysis-independent scaffold function that holds together a tissue-specific nitric oxide synthase multiprotein complex (with ASS1, SLC7A1 and NOS1/NOS2/NOS3), channelling arginine to nitric oxide production and thereby positively regulating nitric oxide biosynthesis.

References

Deep Research

Falcon

Comprehensive Functional Annotation of Human ASL (Argininosuccinate Lyase)

Gene and Protein Identity

1. Enzymatic Function: Reaction and Substrate Specificity

2. Protein Structure and Catalytic Architecture

3. Subcellular Localization and Tissue Distribution

4. Biochemical and Signaling Pathways

4.1 The Urea Cycle

4.2 The Citrulline-NO Cycle

4.3 Arginine as a Metabolic Nexus

5. Evolutionary Conservation and Relationship to δ-Crystallin

6. ASL Deficiency and Disease

6.1 Argininosuccinic Aciduria (ASA)

6.2 Beyond Hyperammonemia: NO Deficiency and Systemic Disease

6.3 Emerging Therapeutic Approaches

7. Summary

Artifacts

Citations

📚 Additional Documentation

Notes

ASL (argininosuccinate lyase, P04424) — review notes

Core enzyme function

Second, non-catalytic (structural) role: nitric oxide production

Disease

Localization

Annotation decisions summary

📄 View Raw YAML