Arginase-1 (liver-type/type I arginase) is the cytosolic, manganese-dependent ureohydrolase that catalyzes the terminal step of the urea cycle, hydrolyzing L-arginine and water to L-ornithine and urea (EC 3.5.3.1). It is a homotrimer, each subunit containing a binuclear manganese cluster required for catalysis. In the liver, where it is most abundantly expressed, arginase-1 regenerates ornithine to sustain the urea cycle and produces the urea that is excreted, making it central to nitrogen disposal; the distinct mitochondrial paralog arginase-2 (ARG2) operates in extrahepatic tissues. Arginase-1 is also constitutively expressed in the granules of human neutrophils and other myeloid cells, where it acts as an immunoregulatory enzyme: released into the extracellular space or phagolysosome, it depletes local L-arginine, suppressing T-cell and NK-cell proliferation and cytokine production and contributing to antimicrobial defense. Loss-of-function variants cause argininemia (arginase deficiency), a urea cycle disorder characterized by progressive spastic diplegia/paraparesis, seizures, and intellectual disability, with hyperammonemia occurring less frequently than in proximal urea cycle disorders.
| GO Term | Evidence | Action | Reason |
|---|---|---|---|
| GO:0004053 arginase activity | IBA GO_REF:0000033 | ACCEPT | Summary: Phylogenetic (PAN-GO) inference of arginase activity, the defining and core molecular function of ARG1. Reason: This is the correct, specific molecular function. Arginase activity (EC 3.5.3.1, L-arginine + H2O = L-ornithine + urea) is directly demonstrated for human ARG1 by crystallographic and enzymatic studies, so the IBA inference is strongly supported. Supporting Evidence: PMID:17562323 Arginase is a manganese metalloenzyme that catalyzes the hydrolysis of l-arginine to yield l-ornithine and urea. |
| GO:0005737 cytoplasm | IBA GO_REF:0000033 | KEEP AS NON CORE | Summary: Phylogenetic inference that ARG1 acts in the cytoplasm; consistent with its established cytosolic localization. Reason: Correct but non-specific. ARG1 is a cytosolic enzyme; the more precise term GO:0005829 (cytosol), also annotated, better captures the localization. Retained as it is not wrong, but subordinate to the cytosol annotation. Supporting Evidence: PMID:21728378 Arginase I is a cytosolic enzyme found predominantly in the liver, and arginase II is a mitochondrial enzyme found at highest concentrations in the kidney. |
| GO:0006525 arginine metabolic process | IBA GO_REF:0000033 | KEEP AS NON CORE | Summary: Phylogenetic inference that ARG1 participates in arginine metabolism; correct but general. Reason: Accurate at a general level. ARG1 catabolizes L-arginine, so involvement in arginine metabolism is correct; the more specific L-arginine catabolic process (GO:0006527) and urea cycle (GO:0000050) annotations capture the precise role. Supporting Evidence: PMID:17562323 Arginase is a manganese metalloenzyme that catalyzes the hydrolysis of l-arginine to yield l-ornithine and urea. |
| GO:0042130 negative regulation of T cell proliferation | IBA GO_REF:0000033 | KEEP AS NON CORE | Summary: Phylogenetic inference of an immunoregulatory role in suppressing T-cell proliferation, corroborated by direct experimental evidence in human granulocyte arginase. Reason: Well-supported secondary (myeloid/immune) function. Extracellular arginase released from human granulocytes depletes arginine and suppresses T-cell proliferation. This is a genuine role but distinct from the core hepatic urea-cycle function. Supporting Evidence: PMID:16709924 Human granulocyte arginase induces a profound suppression of T-cell proliferation and cytokine synthesis. |
| GO:0000050 urea cycle | IBA GO_REF:0000033 | ACCEPT | Summary: Phylogenetic inference that ARG1 participates in the urea cycle; this is a core biological process for the enzyme. Reason: ARG1 catalyzes the terminal step of the urea cycle, regenerating ornithine and releasing urea. This is a core biological process and the IBA inference is strongly supported by direct evidence. Supporting Evidence: PMID:3540966 Arginase (EC 3.5.3.1) catalyzes the last step of the urea cycle in the liver of ureotelic animals. |
| GO:0030145 manganese ion binding | IBA GO_REF:0000033 | ACCEPT | Summary: Phylogenetic inference of manganese ion binding; ARG1 requires a binuclear Mn(2+) cluster for catalysis. Reason: Directly supported by high-resolution crystal structures showing two manganese ions per subunit forming the catalytic binuclear cluster. Core molecular function cofactor requirement. Supporting Evidence: PMID:16141327 The ultrahigh-resolution structure of the human arginase I-ABH complex yields an unprecedented view of the binuclear manganese cluster |
| GO:0005829 cytosol | IBA GO_REF:0000033 | ACCEPT | Summary: Phylogenetic inference that ARG1 acts in the cytosol; this is the established subcellular location of type I arginase. Reason: Arginase I is a cytosolic enzyme (in contrast to mitochondrial ARG2). This is the core localization where ureagenic arginine hydrolysis occurs. Supporting Evidence: PMID:21728378 Arginase I is a cytosolic enzyme found predominantly in the liver, and arginase II is a mitochondrial enzyme found at highest concentrations in the kidney. |
| GO:0004053 arginase activity | IEA GO_REF:0000120 | ACCEPT | Summary: Automated (multiple-method) inference of arginase activity, mapped from RHEA:20569/EC:3.5.3.1 and orthology. Reason: Correct and specific molecular function, consistent with the RHEA reaction L-arginine + H2O = L-ornithine + urea and the experimental annotations. Duplicate of the IBA/EXP arginase-activity annotations, which is acceptable. Supporting Evidence: PMID:16141327 we demonstrate the inhibition of arginase activity by ABH in human and murine myeloid cells |
| GO:0005737 cytoplasm | IEA GO_REF:0000044 | KEEP AS NON CORE | Summary: Automated mapping from the UniProt Cytoplasm subcellular-location keyword. Reason: Correct but general; cytosol (GO:0005829) is the more precise term for this cytosolic enzyme. Retained as a valid broader localization. Supporting Evidence: PMID:16141327 exploration of inhibition in the immune response |
| GO:0006525 arginine metabolic process | IEA GO_REF:0000002 | KEEP AS NON CORE | Summary: InterPro2GO mapping (arginase domain) to arginine metabolic process. Reason: Correct but general. The specific catabolic role (L-arginine catabolic process, GO:0006527) and urea cycle (GO:0000050) better capture ARG1's function; this broad parent is acceptable as an IEA. Supporting Evidence: PMID:17562323 Arginase is a manganese metalloenzyme that catalyzes the hydrolysis of l-arginine to yield l-ornithine and urea. |
| GO:0016813 hydrolase activity, acting on carbon-nitrogen (but not peptide) bonds, in linear amidines | IEA GO_REF:0000002 | MODIFY | Summary: InterPro2GO mapping (ureohydrolase Mn-binding site) to a broad hydrolase-on-C-N-linear-amidines term. Reason: This is the parent term of the specific and experimentally established arginase activity (GO:0004053). Arginase hydrolyzes the C-N bond of the linear amidine L-arginine, so the term is not wrong, but it is over-general given the precise activity is known. Replace with the specific molecular function. Proposed replacements: arginase activity Supporting Evidence: PMID:21728378 Arginase is a binuclear manganese metalloenzyme that hydrolyzes L-arginine to form L-ornithine and urea |
| GO:0042127 regulation of cell population proliferation | IEA GO_REF:0000117 | MARK AS OVER ANNOTATED | Summary: ARBA machine-learning inference of a general role in regulating cell population proliferation. Reason: Overly general electronic annotation. ARG1's proliferation-related effects are specifically on immune cells via arginine depletion (captured by the more specific negative regulation of T-cell proliferation terms). This broad, direction-less parent adds no functional specificity and is likely an over-annotation. Supporting Evidence: PMID:16709924 Human granulocyte arginase induces a profound suppression of T-cell proliferation and cytokine synthesis. |
| GO:0046872 metal ion binding | IEA GO_REF:0000002 | MODIFY | Summary: InterPro2GO mapping to a generic metal ion binding term. Reason: The specific metal bound is known to be manganese (a binuclear Mn(2+) cluster, two ions per subunit), captured by GO:0030145 (manganese ion binding), which is also annotated. The generic parent should be specialized. Proposed replacements: manganese ion binding Supporting Evidence: PMID:16141327 The ultrahigh-resolution structure of the human arginase I-ABH complex yields an unprecedented view of the binuclear manganese cluster |
| GO:0042832 defense response to protozoan | IEA GO_REF:0000107 | KEEP AS NON CORE | Summary: Ensembl-Compara orthology transfer from mouse Arg1 (Q61176) of a role in antiprotozoal defense. Reason: This is an orthology-transferred (GO_REF:0000107, from mouse) immune role consistent with ARG1's known myeloid arginine-depletion function in antimicrobial defense, but it is a peripheral/species-informed role rather than the core hepatic function. Retained as non-core; the underlying human evidence is indirect. Supporting Evidence: PMID:15546957 arginase I is localized in azurophil granules of neutrophils and constitutes a novel antimicrobial effector pathway, likely through arginine depletion in the phagolysosome |
| GO:0046007 negative regulation of activated T cell proliferation | IEA GO_REF:0000107 | KEEP AS NON CORE | Summary: Ensembl-Compara orthology transfer from mouse Arg1 of negative regulation of activated T-cell proliferation. Reason: Consistent with the well-documented human function whereby extracellular/granulocyte arginase depletes arginine and suppresses T-cell proliferation. A genuine secondary immunoregulatory role; retained as non-core. Supporting Evidence: PMID:16709924 Human granulocyte arginase induces a profound suppression of T-cell proliferation and cytokine synthesis. |
| GO:2000552 negative regulation of T-helper 2 cell cytokine production | IEA GO_REF:0000107 | KEEP AS NON CORE | Summary: Ensembl-Compara orthology transfer from mouse Arg1 of a role in limiting Th2 cytokine production. Reason: Orthology-transferred (from mouse) immunoregulatory role. ARG1's arginine depletion suppresses T-cell cytokine synthesis; this specific Th2 term reflects the mouse ILC2/type-2 inflammation context. Retained as a plausible non-core immune role; the direct human evidence is limited. Supporting Evidence: PMID:16709924 Human granulocyte arginase induces a profound suppression of T-cell proliferation and cytokine synthesis. |
| GO:0000050 urea cycle | IEA GO_REF:0000041 | ACCEPT | Summary: UniPathway mapping (UPA00158) to the urea cycle. Reason: Correct core biological process. ARG1 performs the terminal step of the urea cycle. Duplicate of the IBA urea-cycle annotation, which is acceptable. Supporting Evidence: PMID:3540966 Arginase (EC 3.5.3.1) catalyzes the last step of the urea cycle in the liver of ureotelic animals. |
| GO:0070947 neutrophil-mediated killing of fungus | IMP PMID:15546957 Arginase I is constitutively expressed in human granulocytes... | KEEP AS NON CORE | Summary: Experimental (IMP) annotation from the study showing arginase I in azurophil granules participates in fungicidal activity of human neutrophils. Reason: Supported by the cited experimental study demonstrating a granulocyte antimicrobial effector role via arginine depletion. This is a genuine, well-evidenced secondary function in myeloid cells, distinct from the core hepatic urea-cycle role. Note UniProt now uses the closely related term GO:0070965 (positive regulation of neutrophil mediated killing of fungus) for the same evidence. Supporting Evidence: PMID:15546957 arginase I is localized in azurophil granules of neutrophils and constitutes a novel antimicrobial effector pathway, likely through arginine depletion in the phagolysosome |
| GO:0006527 L-arginine catabolic process | IMP PMID:22959135 Analysis of novel ARG1 mutations causing hyperargininemia an... | ACCEPT | Summary: Experimental (IMP) annotation from analysis of ARG1 mutations causing hyperargininemia, correlating loss of arginase activity with impaired L-arginine catabolism. Reason: Core biological process. ARG1 catalyzes the breakdown of L-arginine; loss-of-function mutations cause hyperargininemia (accumulation of arginine), directly demonstrating its role in L-arginine catabolism. The curator assessed erythrocyte enzyme activity across a patient mutation series. Supporting Evidence: PMID:22959135 It is caused by the deficient activity of the enzyme arginase I, encoded by the gene ARG1. |
| GO:0005829 cytosol | TAS Reactome:R-HSA-9956512 | ACCEPT | Summary: Reactome traceable-author annotation (ARG1 variant reaction) placing ARG1 in the cytosol. Reason: Correct core localization for the cytosolic type I arginase. Consistent with the IBA cytosol annotation and biochemical evidence. Supporting Evidence: PMID:21728378 Arginase I is a cytosolic enzyme found predominantly in the liver, and arginase II is a mitochondrial enzyme found at highest concentrations in the kidney. |
| GO:0004053 arginase activity | EXP PMID:16141327 Crystal structure of human arginase I at 1.29-A resolution a... | ACCEPT | Summary: Direct experimental evidence of arginase activity from the 1.29-A crystal structure and inhibition study of human arginase I. Reason: Core molecular function established by direct enzymatic assay and structural characterization of catalysis, including inhibition of arginase activity in human myeloid cells. Supporting Evidence: PMID:16141327 we demonstrate the inhibition of arginase activity by ABH in human and murine myeloid cells |
| GO:0004053 arginase activity | EXP PMID:17562323 Expression, purification, assay, and crystal structure of pe... | ACCEPT | Summary: Direct experimental evidence that (perdeuterated) human arginase I catalyzes hydrolysis of L-arginine to L-ornithine and urea with wild-type activity. Reason: Core molecular function, directly assayed. The enzyme is explicitly characterized as a manganese metalloenzyme catalyzing L-arginine hydrolysis. Supporting Evidence: PMID:17562323 Arginase is a manganese metalloenzyme that catalyzes the hydrolysis of l-arginine to yield l-ornithine and urea. |
| GO:0004053 arginase activity | EXP PMID:21728378 Binding of alpha,alpha-disubstituted amino acids to arginase... | ACCEPT | Summary: Direct experimental evidence (kinetic assay plus crystal structures) of human arginase I catalytic activity. Reason: Core molecular function, directly measured. The enzyme is characterized as a binuclear manganese metalloenzyme hydrolyzing L-arginine to L-ornithine and urea. Supporting Evidence: PMID:21728378 Arginase is a binuclear manganese metalloenzyme that hydrolyzes L-arginine to form L-ornithine and urea |
| GO:0005737 cytoplasm | EXP PMID:16141327 Crystal structure of human arginase I at 1.29-A resolution a... | KEEP AS NON CORE | Summary: Experimental subcellular localization of ARG1 to the cytoplasm. Reason: Correct but general. The more precise cytosol term (GO:0005829) better captures the localization of this cytosolic enzyme. Retained as a valid broader annotation. Supporting Evidence: PMID:21728378 Arginase I is a cytosolic enzyme found predominantly in the liver, and arginase II is a mitochondrial enzyme found at highest concentrations in the kidney. |
| GO:0005515 protein binding | IPI PMID:28813417 CMTM6 maintains the expression of PD-L1 and regulates anti-t... | MARK AS OVER ANNOTATED | Summary: IPI annotation recording an ARG1-CMTM6 interaction detected by mass spectrometry in a study focused on CMTM6-mediated regulation of PD-L1. Reason: Bare "protein binding" is uninformative and does not describe a molecular function. The supporting paper is a CRISPR/proteomics study of CMTM6 as a regulator of PD-L1; ARG1 appears only as one mass-spectrometry co-precipitant of CMTM6, with no evidence that this interaction is functionally relevant to ARG1. Per curation guidelines, avoid uninformative protein binding terms; this should not be treated as a core function. Supporting Evidence: PMID:28813417 CMTM6 is a ubiquitously expressed protein that binds PD-L1 and maintains its cell surface expression. |
| GO:0005576 extracellular region | IDA PMID:16709924 Suppression of T-cell functions by human granulocyte arginas... | KEEP AS NON CORE | Summary: Direct experimental evidence that arginase I is liberated from human granulocytes and accumulates extracellularly during inflammation. Reason: Genuine, experimentally demonstrated secondary localization. Neutrophil arginase is released into the extracellular space, where it depletes arginine. This is real but peripheral to the core intracellular (cytosolic) hepatic function. Supporting Evidence: PMID:16709924 arginase I is liberated from human granulocytes, and very high activities accumulate extracellularly during purulent inflammatory reactions |
| GO:0042130 negative regulation of T cell proliferation | IDA PMID:16709924 Suppression of T-cell functions by human granulocyte arginas... | KEEP AS NON CORE | Summary: Direct experimental evidence that human granulocyte arginase suppresses T-cell proliferation via arginine depletion. Reason: Well-supported secondary immunoregulatory function. Extracellular arginase depletes arginine, downregulating CD3-zeta and suppressing T-cell proliferation. Genuine but distinct from the core urea-cycle role. Supporting Evidence: PMID:16709924 This T-cell phenotype is due to arginase-mediated depletion of arginine in the T-cell environment, which leads to CD3zeta chain down-regulation but does not alter T-cell viability |
| GO:0060336 negative regulation of type II interferon-mediated signaling pathway | IMP PMID:16709924 Suppression of T-cell functions by human granulocyte arginas... | KEEP AS NON CORE | Summary: IMP annotation of a downstream effect on IFN-gamma signaling, linked to arginase-mediated suppression of T-cell cytokine synthesis. Reason: A downstream immunoregulatory consequence of arginine depletion (suppressed T-cell cytokine synthesis, including IFN-gamma responses) rather than a direct biochemical function of ARG1. Retained as non-core; the curator (UniProt) made this annotation from the full text. Supporting Evidence: PMID:16709924 Human granulocyte arginase induces a profound suppression of T-cell proliferation and cytokine synthesis. |
| GO:0005576 extracellular region | TAS Reactome:R-HSA-6798749 | KEEP AS NON CORE | Summary: Reactome annotation (exocytosis of specific granule lumen proteins) placing ARG1 in the extracellular region upon neutrophil degranulation. Reason: Consistent with the experimentally demonstrated release of neutrophil arginase into the extracellular space during degranulation. A genuine secondary localization, non-core relative to the cytosolic hepatic function. Supporting Evidence: PMID:16709924 arginase I is liberated from human granulocytes, and very high activities accumulate extracellularly during purulent inflammatory reactions |
| GO:0005576 extracellular region | TAS Reactome:R-HSA-6798751 | KEEP AS NON CORE | Summary: Reactome annotation (exocytosis of azurophil granule lumen proteins) placing ARG1 in the extracellular region upon neutrophil degranulation. Reason: Same as the other extracellular-region annotations - reflects release of granule-stored neutrophil arginase. Genuine secondary localization; non-core. Supporting Evidence: PMID:15546957 arginase I is localized in azurophil granules of neutrophils and constitutes a novel antimicrobial effector pathway, likely through arginine depletion in the phagolysosome |
| GO:0035578 azurophil granule lumen | TAS Reactome:R-HSA-6798751 | KEEP AS NON CORE | Summary: Reactome annotation placing ARG1 in the azurophil granule lumen of neutrophils. Reason: Directly supported by experimental localization of arginase I to azurophil granules of neutrophils. A genuine myeloid-cell localization, non-core relative to the core cytosolic hepatic function. Supporting Evidence: PMID:15546957 arginase I is localized in azurophil granules of neutrophils and constitutes a novel antimicrobial effector pathway, likely through arginine depletion in the phagolysosome |
| GO:0035580 specific granule lumen | TAS Reactome:R-HSA-6798749 | KEEP AS NON CORE | Summary: Reactome annotation placing ARG1 in the specific granule lumen of neutrophils. Reason: Reflects the granule storage of arginase I in neutrophils (the primary experimental report emphasizes azurophil granules; Reactome models both granule compartments). Genuine myeloid localization, non-core. Supporting Evidence: PMID:15546957 in human leukocytes arginase I is constitutively expressed only in granulocytes |
| GO:0005634 nucleus | HDA PMID:21630459 Proteomic characterization of the human sperm nucleus. | MARK AS OVER ANNOTATED | Summary: High-throughput proteomics detection of ARG1 in an isolated human sperm nucleus fraction. Reason: This annotation derives from a large-scale catalog of 403 proteins detected in isolated sperm nuclei, not from a targeted study of nuclear ARG1 function. ARG1 is a well-established cytosolic enzyme with no known nuclear function; the detection likely reflects abundant cytoplasmic protein carryover in a bulk proteomic fraction. Marked as over-annotated rather than removed, as a mass-spec detection. Supporting Evidence: PMID:21630459 403 different proteins have been identified from the isolated sperm nuclei |
| GO:0005829 cytosol | TAS Reactome:R-HSA-70569 | ACCEPT | Summary: Reactome annotation (arginine + H2O => ornithine + urea reaction) placing ARG1 in the cytosol. Reason: Core localization. This Reactome reaction is precisely the arginase reaction, correctly localized to the cytosol where the cytosolic type I arginase acts. Supporting Evidence: PMID:21728378 Arginase I is a cytosolic enzyme found predominantly in the liver, and arginase II is a mitochondrial enzyme found at highest concentrations in the kidney. |
| GO:0005829 cytosol | TAS Reactome:R-HSA-9959871 | ACCEPT | Summary: Reactome annotation (ARG1 gene expression) associated with cytosolic localization. Reason: Correct core localization for the cytosolic type I arginase; duplicate of the other cytosol annotations, which is acceptable. Supporting Evidence: PMID:21728378 Arginase I is a cytosolic enzyme found predominantly in the liver, and arginase II is a mitochondrial enzyme found at highest concentrations in the kidney. |
| GO:0004053 arginase activity | TAS PMID:3540966 Molecular cloning and nucleotide sequence of cDNA for human ... | ACCEPT | Summary: Traceable-author statement of arginase activity from the original cloning of human liver arginase cDNA. Reason: Core molecular function. The cloned cDNA conferred arginase activity on E. coli, and the enzyme is identified as EC 3.5.3.1 catalyzing the last urea-cycle step. Duplicate of the experimental arginase-activity annotations, which is acceptable. Supporting Evidence: PMID:3540966 Arginase activity was detected in Escherichia coli cells transformed with the plasmid carrying lambda hARG6 cDNA insert. |
| GO:0005737 cytoplasm | TAS PMID:3540966 Molecular cloning and nucleotide sequence of cDNA for human ... | KEEP AS NON CORE | Summary: Traceable-author statement of cytoplasmic (liver) arginase localization. Reason: Correct but general; cytosol (GO:0005829) is the more precise term. Retained as a valid broader localization. Supporting Evidence: PMID:21728378 Arginase I is a cytosolic enzyme found predominantly in the liver, and arginase II is a mitochondrial enzyme found at highest concentrations in the kidney. |
| GO:0006527 L-arginine catabolic process | TAS PMID:3540966 Molecular cloning and nucleotide sequence of cDNA for human ... | ACCEPT | Summary: Traceable-author statement of ARG1's role in L-arginine catabolism (the terminal urea-cycle step) from the original cloning paper. Reason: Core biological process. ARG1 hydrolyzes L-arginine as the last step of the urea cycle. Duplicate of the IMP L-arginine catabolic process annotation, which is acceptable. Supporting Evidence: PMID:3540966 Arginase (EC 3.5.3.1) catalyzes the last step of the urea cycle in the liver of ureotelic animals. |
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Download this section (compressed HTML)Q: Beyond arginine depletion in the extracellular space/phagolysosome, does human ARG1 have any direct, arginine-independent immunoregulatory function, or are all of its immune effects a consequence of local arginine catabolism?
Q: Is the reported nuclear detection of ARG1 in sperm (PMID:21630459) functionally meaningful, or does it reflect cytoplasmic carryover in bulk proteomics?
Experiment: Structure-guided kinetic characterization of clinically observed missense variants (e.g. those affecting the Mn-binding residues or the R308 trimerization interface) to correlate residual arginase activity with argininemia phenotype severity.
Hypothesis: Argininemia severity is determined by residual arginase activity, which depends on how a given missense variant perturbs the Mn-binding active site or the R308 trimerization interface.
Experiment: Quantitative measurement of local arginine depletion and downstream T-cell CD3-zeta levels using ARG1-deficient versus wild-type human neutrophils to dissect the enzymatic basis of the immunosuppressive effect.
Hypothesis: The immunosuppressive effect of neutrophil ARG1 is entirely due to enzymatic depletion of extracellular L-arginine.
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