hisH encodes the class-I glutamine amidotransferase subunit of imidazole-glycerol-phosphate synthase (IGPS). HisH hydrolyzes L-glutamine and channels the resulting ammonia to the HisF cyclase subunit, which converts PRFAR to imidazole-glycerol phosphate and AICAR. The coupled HisF-HisH reaction is the fifth step of L-histidine biosynthesis.
| GO Term | Evidence | Action | Reason |
|---|---|---|---|
| GO:0000105 L-histidine biosynthetic process | IEA GO_REF:0000120 | ACCEPT | Summary: HisH is an obligate component of the fifth histidine-biosynthesis reaction. Reason: UniProt, UniPathway, and HisH-specific family assignments place the HisF-HisH IGPS reaction at step 5 of 9 in L-histidine biosynthesis. |
| GO:0000107 imidazoleglycerol-phosphate synthase activity | IEA GO_REF:0000120 | ACCEPT | Summary: HisH contributes the ammonia-generating subunit of IGPS activity. Reason: GO:0000107 and RHEA:24793 describe the coupled HisF-HisH reaction. HisH supplies channelled ammonia while HisF performs the cyclization chemistry. Support is the HAMAP-rule (MF_00278) FUNCTION and SUBUNIT text plus HisH family membership (NCBIfam TIGR01855, InterPro IPR010139); it describes the HisH-HisF heterodimer, so the IGPS activity is a complex-level activity to which HisH contributes the glutaminase half-reaction. No KT2440 assay is cached. Supporting Evidence: file:PSEPK/hisH/hisH-uniprot.txt IGPS catalyzes the conversion of PRFAR and glutamine to IGP, AICAR and glutamate. file:PSEPK/hisH/hisH-uniprot.txt The HisH subunit catalyzes the hydrolysis of glutamine to glutamate and ammonia as part of the synthesis of IGP and AICAR. file:PSEPK/hisH/hisH-uniprot.txt DR NCBIfam; TIGR01855; IMP_synth_hisH; 1. |
| GO:0004359 glutaminase activity | IEA GO_REF:0000120 | ACCEPT | Summary: HisH catalyzes glutamine hydrolysis as its subunit-level activity. Reason: The reviewed UniProt entry assigns EC 3.5.1.2 and RHEA:15889 and describes glutamine hydrolysis as the source of ammonia channelled to HisF. Supporting Evidence: file:PSEPK/hisH/hisH-uniprot.txt The HisH subunit catalyzes the hydrolysis of file:PSEPK/hisH/hisH-deep-research-openscientist.md catalyzes the hydrolysis of L-glutamine to L-glutamate plus ammonia (EC 3.5.1.2) |
| GO:0005737 cytoplasm | IEA GO_REF:0000120 | KEEP AS NON CORE | Summary: HisH is a soluble cytoplasmic biosynthetic enzyme. Reason: The location is supported by UniProt but is contextual rather than the core biochemical role. |
| GO:0016763 pentosyltransferase activity | IEA GO_REF:0000002 | REMOVE | Summary: HisH does not catalyze pentosyl-group transfer. Reason: The InterPro2GO assignment conflicts with the HisH-specific family, EC 3.5.1.2 glutaminase chemistry, and the composite IGPS reaction. HisH hydrolyzes glutamine to supply ammonia; no pentosyl donor or transfer reaction is involved. |
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