{"id":"069fc175-b89b-581a-8f57-c22d64d2cee3","stable_key":"911fb3c7-8cc3-5667-b677-5682fab67648:histidine-urda-flavin","predicate":"participates_in","statement":"The UrdA catalytic-domain structures contained FAD alongside substrate or product, and assays supported flavin-associated urocanate reduction.","claim_class":"mechanistic","status":"source_derived_draft","evidence_grade":"ungraded","direction":"context_dependent","is_public":true,"mechanism_event_id":"db5669bc-3ea5-5831-8ead-432448ea995b","mechanism_event_label":"This microbial reaction uses a riboflavin-derived chemical tool.","subject":{"id":"e2cd7179-f218-54e8-9ce9-7a836ae35fac","slug":"fad","display_name":"FAD","entity_type_key":"small_molecule"},"object":{"id":"206711aa-90bc-5f09-a2d1-d9541f859f9f","slug":"shewanella-oneidensis-urda","display_name":"Shewanella oneidensis MR-1 urocanate reductase / UrdA","entity_type_key":"protein"},"evidence_count":1,"mechanism_event":{"id":"db5669bc-3ea5-5831-8ead-432448ea995b","stable_key":"911fb3c7-8cc3-5667-b677-5682fab67648:histidine-urda-flavin-event","event_type":"observed_relationship","label":"This microbial reaction uses a riboflavin-derived chemical tool.","description":"The UrdA catalytic-domain structures contained FAD alongside substrate or product, and assays supported flavin-associated urocanate reduction.","status":"provisional","compartment":null,"participants":[{"entity":{"id":"e2cd7179-f218-54e8-9ce9-7a836ae35fac","slug":"fad","display_name":"FAD","entity_type_key":"small_molecule"},"role":"subject","stoichiometry":null,"state_label":"","sequence_order":0,"notes":""},{"entity":{"id":"206711aa-90bc-5f09-a2d1-d9541f859f9f","slug":"shewanella-oneidensis-urda","display_name":"Shewanella oneidensis MR-1 urocanate reductase / UrdA","entity_type_key":"protein"},"role":"target","stoichiometry":null,"state_label":"","sequence_order":1,"notes":""},{"entity":{"id":"44374451-3436-5136-a8ae-5dcc6d8c353b","slug":"histidine","display_name":"L-Histidine","entity_type_key":"small_molecule"},"role":"context_participant","stoichiometry":null,"state_label":"","sequence_order":2,"notes":""},{"entity":{"id":"86f82ca3-8f80-5c1f-b724-27b78660c2a9","slug":"trans-urocanate","display_name":"trans-Urocanate","entity_type_key":"small_molecule"},"role":"context_participant","stoichiometry":null,"state_label":"","sequence_order":3,"notes":""},{"entity":{"id":"06c093ed-025c-54bc-8016-6a3da64ffbf9","slug":"imidazole-propionate","display_name":"Imidazole propionate","entity_type_key":"small_molecule"},"role":"context_participant","stoichiometry":null,"state_label":"","sequence_order":4,"notes":""}]},"contexts":[{"dimension":"evidence_access","value_text":"Primary full text","comparator":null,"unit":null,"notes":"","entity":null},{"dimension":"experimental_model","value_text":"Bacterial structural enzymology; FAD-supplemented enzyme assays.","comparator":null,"unit":null,"notes":"","entity":null},{"dimension":"limitations","value_text":"Does not show that human riboflavin intake limits or increases microbial imidazole-propionate production.","comparator":null,"unit":null,"notes":"","entity":null},{"dimension":"nutrient_topic","value_text":"L-Histidine collection; species, compartment, exposure, co-substrates and manipulation remain explicit.","comparator":null,"unit":null,"notes":"","entity":{"slug":"histidine","display_name":"L-Histidine","entity_type_key":"small_molecule"}},{"dimension":"plain_language","value_text":"This microbial reaction uses a riboflavin-derived chemical tool.","comparator":null,"unit":null,"notes":"","entity":null},{"dimension":"primary_references","value_text":"Structural characterization of the microbial enzyme urocanate reductase mediating imidazole propionate production. · 2021 · https://pubmed.ncbi.nlm.nih.gov/33649331/ · DOI 10.1038/s41467-021-21548-y","comparator":null,"unit":null,"notes":"","entity":null}],"evidence":[{"id":"0260c8b3-8d35-53c9-975f-8181ac35c134","evidence_kind":"source_excerpt","locator":"Lines 274-280","start_line":274,"end_line":280,"excerpt":"## histidine-urda-flavin\nThis microbial reaction uses a riboflavin-derived chemical tool.\nThe UrdA catalytic-domain structures contained FAD alongside substrate or product, and assays supported flavin-associated urocanate reduction.\nModel: Bacterial structural enzymology; FAD-supplemented enzyme assays.\nLimitations: Does not show that human riboflavin intake limits or increases microbial imidazole-propionate production.\nEvidence access: Primary full text\nStructural characterization of the microbial enzyme urocanate reductase mediating imidazole propionate production. · 2021 · https://pubmed.ncbi.nlm.nih.gov/33649331/ · DOI 10.1038/s41467-021-21548-y","model_system":"Bacterial structural enzymology; FAD-supplemented enzyme assays.","directness":"reported_statement","verification_status":"source_derived_draft","notes":"Original curation paraphrase; evidence access and experimental limitations specified.","relationship":"supports","weight":1.0,"link_notes":"","source":{"id":"ce59e6c9-1213-523b-9d0b-400b7a81cd1c","stable_key":"import-911fb3c7-8cc3-5667-b677-5682fab67648","title":"L-Histidine: supply, catabolism, histamine, receptors and cross-nutrient mechanisms (2026-09-19)","document_type":"imported_text","citation_label":"AI-assisted research curation; primary references, access levels and experimental limitations individually identified. 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