{"id":"a3405b1b-24e2-5054-ae67-71122795661b","stable_key":"63ce713e-6aea-59f6-9896-ca30e010b2ce:l-tyrosine-hgd-ring","predicate":"opens_ring_of","statement":"Human HGD catalyzes aromatic-ring cleavage during phenylalanine/tyrosine degradation; its structure contains a coordinated active-site iron ion.","claim_class":"mechanistic","status":"source_derived_draft","evidence_grade":"ungraded","direction":"context_dependent","is_public":true,"mechanism_event_id":"a30ba528-1bba-5459-9f4c-d5a0fe4f6298","mechanism_event_label":"Iron-dependent chemistry opens the aromatic ring for further breakdown.","subject":{"id":"60587707-1969-5d03-a3ba-d03912c5dc40","slug":"hgd","display_name":"Human homogentisate 1,2-dioxygenase / HGD","entity_type_key":"protein"},"object":{"id":"ea7ed42c-7c9f-5d5a-912a-7b67e60df93e","slug":"homogentisate","display_name":"Homogentisate","entity_type_key":"small_molecule"},"evidence_count":1,"mechanism_event":{"id":"a30ba528-1bba-5459-9f4c-d5a0fe4f6298","stable_key":"63ce713e-6aea-59f6-9896-ca30e010b2ce:l-tyrosine-hgd-ring-event","event_type":"observed_relationship","label":"Iron-dependent chemistry opens the aromatic ring for further breakdown.","description":"Human HGD catalyzes aromatic-ring cleavage during phenylalanine/tyrosine degradation; its structure contains a coordinated active-site iron ion.","status":"provisional","compartment":null,"participants":[{"entity":{"id":"60587707-1969-5d03-a3ba-d03912c5dc40","slug":"hgd","display_name":"Human homogentisate 1,2-dioxygenase / HGD","entity_type_key":"protein"},"role":"subject","stoichiometry":null,"state_label":"","sequence_order":0,"notes":""},{"entity":{"id":"ea7ed42c-7c9f-5d5a-912a-7b67e60df93e","slug":"homogentisate","display_name":"Homogentisate","entity_type_key":"small_molecule"},"role":"target","stoichiometry":null,"state_label":"","sequence_order":1,"notes":""},{"entity":{"id":"bcfef85f-831d-5439-ba51-1aef4b090441","slug":"l-tyrosine","display_name":"L-Tyrosine","entity_type_key":"small_molecule"},"role":"context_participant","stoichiometry":null,"state_label":"","sequence_order":2,"notes":""},{"entity":{"id":"a4a0785d-bd5f-56e3-ad95-8c1ceff53bfa","slug":"maleylacetoacetate","display_name":"Maleylacetoacetate","entity_type_key":"small_molecule"},"role":"context_participant","stoichiometry":null,"state_label":"","sequence_order":3,"notes":""},{"entity":{"id":"89bcaf42-b4ab-5760-8c2e-44eace10cee0","slug":"iron","display_name":"Iron","entity_type_key":"nutrient_element"},"role":"context_participant","stoichiometry":null,"state_label":"","sequence_order":4,"notes":""},{"entity":{"id":"899c7ab0-6f81-5b38-a6bd-fbb33d66ac8d","slug":"oxygen","display_name":"Molecular oxygen","entity_type_key":"small_molecule"},"role":"context_participant","stoichiometry":null,"state_label":"","sequence_order":5,"notes":""}]},"contexts":[{"dimension":"evidence_access","value_text":"Primary abstract","comparator":null,"unit":null,"notes":"","entity":null},{"dimension":"experimental_model","value_text":"Human apo and iron-bound HGD crystallography.","comparator":null,"unit":null,"notes":"","entity":null},{"dimension":"limitations","value_text":"The study is structural/enzymatic evidence, not a trial of iron supplementation.","comparator":null,"unit":null,"notes":"","entity":null},{"dimension":"nutrient_topic","value_text":"L-Tyrosine collection; species, compartment, exposure, co-substrates and manipulation remain explicit.","comparator":null,"unit":null,"notes":"","entity":{"slug":"l-tyrosine","display_name":"L-Tyrosine","entity_type_key":"small_molecule"}},{"dimension":"plain_language","value_text":"Iron-dependent chemistry opens the aromatic ring for further breakdown.","comparator":null,"unit":null,"notes":"","entity":null},{"dimension":"primary_references","value_text":"Crystal structure of human homogentisate dioxygenase. · 2000 · https://pubmed.ncbi.nlm.nih.gov/10876237/ · DOI 10.1038/76756","comparator":null,"unit":null,"notes":"","entity":null}],"evidence":[{"id":"4555f44e-3c2a-588a-81dc-23f1ee2c7747","evidence_kind":"source_excerpt","locator":"Lines 236-242","start_line":236,"end_line":242,"excerpt":"## l-tyrosine-hgd-ring\nIron-dependent chemistry opens the aromatic ring for further breakdown.\nHuman HGD catalyzes aromatic-ring cleavage during phenylalanine/tyrosine degradation; its structure contains a coordinated active-site iron ion.\nModel: Human apo and iron-bound HGD crystallography.\nLimitations: The study is structural/enzymatic evidence, not a trial of iron supplementation.\nEvidence access: Primary abstract\nCrystal structure of human homogentisate dioxygenase. · 2000 · https://pubmed.ncbi.nlm.nih.gov/10876237/ · DOI 10.1038/76756","model_system":"Human apo and iron-bound HGD crystallography.","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":"12917df2-c6e0-5b61-850f-dbff6d4b4d30","stable_key":"import-63ce713e-6aea-59f6-9896-ca30e010b2ce","title":"L-Tyrosine: catecholamines, thyroid chemistry, pigment, metabolism 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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