ArgJ (PP_1346) is an inferred cytoplasmic ornithine acetyltransferase that transfers the acetyl group from N-acetyl-L-ornithine to L-glutamate, releasing ornithine and regenerating N-acetylglutamate for L-arginine biosynthesis. Whether the KT2440 enzyme also uses acetyl-CoA efficiently is unresolved; endogenous ArgJ does not prevent arginine auxotrophy after loss of ArgA under tested conditions.
| GO Term | Evidence | Action | Reason |
|---|---|---|---|
| GO:0004042 L-glutamate N-acetyltransferase activity, acting on acetyl-CoA as donor | IEA GO_REF:0000120 | MARK AS OVER ANNOTATED | Summary: HAMAP propagates the acetyl-CoA-dependent initiating activity to KT2440 ArgJ, but no target assay exists and native genetics shows that ArgJ does not replace the dedicated ArgA initiation enzyme. Reason: The HAMAP rule assigns both ArgJ reactions to every family member. Mono- and bifunctional ArgJ proteins coexist (PMID:10931207), and PMID:17347518 cautions that family membership does not establish the second, acetyl-CoA-dependent activity. In KT2440, argA mutants are arginine auxotrophs (PMID:31451546), so any residual ArgJ initiating activity does not substitute for ArgA in vivo. Residual in vitro activity is not excluded, so the row is not removed; it is marked as an over-annotation of a secondary activity of unknown relevance, and the recycling activity (GO:0004358) remains the core ArgJ function. Supporting Evidence: PMID:17347518 Not all OATs possess this dual activity file:PSEPK/argJ/argJ-uniprot.txt Reaction=L-glutamate + acetyl-CoA = N-acetyl-L-glutamate + CoA + H(+); |
| GO:0004358 L-glutamate N-acetyltransferase activity, acting on acetyl-L-ornithine as donor | IEA GO_REF:0000120 | ACCEPT | Summary: ArgJ transfers acetyl from N-acetyl-L-ornithine to glutamate, releasing ornithine. Reason: Reviewed UniProt assigns EC 2.3.1.35 and RHEA:15349 as the second defining ArgJ activity. This assignment uses curated catalytic/family evidence; it is not a direct purified-enzyme measurement in KT2440. Supporting Evidence: file:PSEPK/argJ/argJ-uniprot.txt Reaction=N(2)-acetyl-L-ornithine + L-glutamate = N-acetyl-L-glutamate + L-ornithine; |
| GO:0005737 cytoplasm | IEA GO_REF:0000120 | ACCEPT | Summary: The cytoplasm is the inferred compartment of this soluble biosynthetic enzyme. Reason: This location is part of the core metabolic role. It is supported by conserved soluble-enzyme biology and curated UniProt/HAMAP localization, not direct target imaging. Supporting Evidence: file:PSEPK/argJ/argJ-uniprot.txt SUBCELLULAR LOCATION: Cytoplasm |
| GO:0006526 L-arginine biosynthetic process | IEA GO_REF:0000120 | ACCEPT | Summary: The enzyme contributes catalytic chemistry to L-arginine biosynthesis. Reason: The enzyme catalyzes a chemical step of the acetylated-ornithine route to arginine, supported by curated reaction and family classification. The native insertion mutant remains prototrophic (PMID31451546), compatible with metabolic redundancy; this does not demonstrate inactivity or identify its compensator. Supporting Evidence: file:PSEPK/argJ/argJ-uniprot.txt Reaction=N(2)-acetyl-L-ornithine + L-glutamate = N-acetyl-L-glutamate + L-ornithine; PMID:31451546 It should be noted that these three mutants do not display arginine auxotrophy |
| GO:0006592 L-ornithine biosynthetic process | IEA GO_REF:0000118 | ACCEPT | Summary: ArgJ directly releases L-ornithine from N-acetyl-L-ornithine. Reason: The EC 2.3.1.35 transacetylation reaction produces ornithine in the cyclic route. Supporting Evidence: file:PSEPK/argJ/argJ-uniprot.txt Reaction=N(2)-acetyl-L-ornithine + L-glutamate = N-acetyl-L-glutamate + L-ornithine; |
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Download this section (compressed HTML)Q: Does purified KT2440 ArgJ use acetyl-CoA as well as acetylornithine, and can any measured initiation activity support growth without ArgA?
Experiment: Measure acetyl transfer from acetylornithine and acetyl-CoA to glutamate with purified PP_1346, and test complementation of argA and argJ mutants under defined media conditions.
Type: substrate-specific enzyme kinetics and complementation
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