{"id":"2c6a757a-1291-59ad-9405-f5d964636787","stable_key":"a9dd23c6-978a-5755-8bd8-f29bd1fe0cda:b3-pre-haao-iron","predicate":"cofactor-for","statement":"Crystallography and metal characterization identified iron in the active site of human HAAO, with spectroscopic behavior consistent with the ferrous preparation before air oxidation.","claim_class":"mechanistic","status":"source_derived_draft","evidence_grade":"ungraded","direction":"positive","is_public":true,"mechanism_event_id":"a87b056f-5439-511d-819b-59816c4c0481","mechanism_event_label":"A second iron-containing enzyme acts farther along the tryptophan route.","subject":{"id":"59d6d1cd-df32-5b58-b950-3188bc7b95d6","slug":"iron-ii","display_name":"Ferrous iron","entity_type_key":"ion"},"object":{"id":"1c637210-ac90-55bd-9af1-8bf3634fa221","slug":"haao","display_name":"Human 3-hydroxyanthranilate 3,4-dioxygenase / HAAO","entity_type_key":"protein"},"evidence_count":1,"mechanism_event":{"id":"a87b056f-5439-511d-819b-59816c4c0481","stable_key":"a9dd23c6-978a-5755-8bd8-f29bd1fe0cda:b3-pre-haao-iron-event","event_type":"biochemical_relationship","label":"A second iron-containing enzyme acts farther along the tryptophan route.","description":"Crystallography and metal characterization identified iron in the active site of human HAAO, with spectroscopic behavior consistent with the ferrous preparation before air oxidation.","status":"provisional","compartment":null,"participants":[{"entity":{"id":"59d6d1cd-df32-5b58-b950-3188bc7b95d6","slug":"iron-ii","display_name":"Ferrous iron","entity_type_key":"ion"},"role":"native catalytic metal","stoichiometry":null,"state_label":"","sequence_order":0,"notes":""},{"entity":{"id":"1c637210-ac90-55bd-9af1-8bf3634fa221","slug":"haao","display_name":"Human 3-hydroxyanthranilate 3,4-dioxygenase / HAAO","entity_type_key":"protein"},"role":"enzyme","stoichiometry":null,"state_label":"","sequence_order":1,"notes":""},{"entity":{"id":"f73f064a-cc62-5755-8563-41ef84e86df9","slug":"3-hydroxyanthranilate","display_name":"3-Hydroxyanthranilate","entity_type_key":"small_molecule"},"role":"pathway substrate","stoichiometry":null,"state_label":"","sequence_order":2,"notes":""}]},"contexts":[{"dimension":"cross_nutrient","value_text":"Nonheme iron participates in a downstream tryptophan/niacin pathway enzyme; nutritional iron restriction was not tested.","comparator":null,"unit":null,"notes":"","entity":null},{"dimension":"evidence_span","value_text":"{\"source_cache\": \"artifacts/niacin-precursors-sources/haao2017.paragraphs.txt\", \"locator\": \"Normalized full-text paragraphs 33–33 (0-based)\", \"start_char\": 22514, \"end_char\": 24337, \"file_sha256\": \"d02386a59595104ccae2e62943e69030930da86ec005769b469f2001e31a6eb5\", \"text_sha256\": \"4c47aa3f5cdc1fd3c776752c345f1d60e4833d0e3b7e8227c574ae086c3b1783\"}","comparator":null,"unit":null,"notes":"","entity":null},{"dimension":"experimental_model","value_text":"Purified human HAAO metal-containing crystal structures and ICP-MS/XRF/EPR characterization","comparator":null,"unit":null,"notes":"","entity":null},{"dimension":"exposure","value_text":"Biochemical or structural assay; no dietary intervention","comparator":null,"unit":null,"notes":"","entity":null},{"dimension":"limitations","value_text":"Purified-enzyme evidence does not establish dietary intake requirements or clinical outcomes.","comparator":null,"unit":null,"notes":"","entity":null},{"dimension":"nutrient_topic","value_text":"Niacin research collection; topical membership is not evidence of a direct dietary effect.","comparator":null,"unit":null,"notes":"","entity":{"slug":"niacin","display_name":"Niacin (vitamin B3)","entity_type_key":"nutrient_element"}},{"dimension":"organism","value_text":"Homo sapiens","comparator":null,"unit":null,"notes":"","entity":null},{"dimension":"plain_language","value_text":"A second iron-containing enzyme acts farther along the tryptophan route.","comparator":null,"unit":null,"notes":"","entity":null},{"dimension":"primary_references","value_text":"[b3-pre-haao2017] Crystal structures of human 3-hydroxyanthranilate 3,4-dioxygenase with native and non-native metals bound in the active site. (2017). https://pubmed.ncbi.nlm.nih.gov/28375145/ DOI: 10.1107/s2059798317002029","comparator":null,"unit":null,"notes":"","entity":null},{"dimension":"tissue_or_cell_type","value_text":"Purified recombinant protein; no intact tissue","comparator":null,"unit":null,"notes":"","entity":null}],"evidence":[{"id":"469ffc1b-da92-5301-a08a-5dae9e79695c","evidence_kind":"source_excerpt","locator":"Lines 507-519","start_line":507,"end_line":519,"excerpt":"### b3-pre-haao-iron\nCrystallography and metal characterization identified iron in the active site of human HAAO, with spectroscopic behavior consistent with the ferrous preparation before air oxidation.\nCondition category: normal\nnutrient_topic: Niacin research collection; topical membership is not evidence of a direct dietary effect.\nplain_language: A second iron-containing enzyme acts farther along the tryptophan route.\norganism: Homo sapiens\ntissue_or_cell_type: Purified recombinant protein; no intact tissue\nexperimental_model: Purified human HAAO metal-containing crystal structures and ICP-MS/XRF/EPR characterization\nlimitations: Purified-enzyme evidence does not establish dietary intake requirements or clinical outcomes.\nexposure: Biochemical or structural assay; no dietary intervention\ncross_nutrient: Nonheme iron participates in a downstream tryptophan/niacin pathway enzyme; nutritional iron restriction was not tested.\nevidence_span: {\"source_cache\": \"artifacts/niacin-precursors-sources/haao2017.paragraphs.txt\", \"locator\": \"Normalized full-text paragraphs 33–33 (0-based)\", \"start_char\": 22514, \"end_char\": 24337, \"file_sha256\": \"d02386a59595104ccae2e62943e69030930da86ec005769b469f2001e31a6eb5\", \"text_sha256\": \"4c47aa3f5cdc1fd3c776752c345f1d60e4833d0e3b7e8227c574ae086c3b1783\"}\n[b3-pre-haao2017] Crystal structures of human 3-hydroxyanthranilate 3,4-dioxygenase with native and non-native metals bound in the active site. 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