{"id":"abe1e4bc-b31e-55a7-9944-654c5e6a49ee","stable_key":"911fb3c7-8cc3-5667-b677-5682fab67648:histidine-hnmt-variant","predicate":"modifies_tested","statement":"Recombinant Ile105 HNMT had about 16 percent lower specific activity and higher apparent Km for SAM and histamine than Thr105 across 25-45 degrees C.","claim_class":"mechanistic","status":"source_derived_draft","evidence_grade":"ungraded","direction":"context_dependent","is_public":true,"mechanism_event_id":"450179aa-c36d-581c-ac85-0b94e7850fe6","mechanism_event_label":"A common enzyme variant changed the measured reaction kinetics.","subject":{"id":"a400cc7e-73aa-5ad0-8a51-834398130b44","slug":"human-hnmt-thr105ile","display_name":"Human HNMT Thr105Ile variation","entity_type_key":"cellular_process"},"object":{"id":"470c158d-c9b9-5b79-b743-771272e353e8","slug":"hnmt","display_name":"Human histamine N-methyltransferase / HNMT","entity_type_key":"protein"},"evidence_count":1,"mechanism_event":{"id":"450179aa-c36d-581c-ac85-0b94e7850fe6","stable_key":"911fb3c7-8cc3-5667-b677-5682fab67648:histidine-hnmt-variant-event","event_type":"observed_relationship","label":"A common enzyme variant changed the measured reaction kinetics.","description":"Recombinant Ile105 HNMT had about 16 percent lower specific activity and higher apparent Km for SAM and histamine than Thr105 across 25-45 degrees C.","status":"provisional","compartment":null,"participants":[{"entity":{"id":"a400cc7e-73aa-5ad0-8a51-834398130b44","slug":"human-hnmt-thr105ile","display_name":"Human HNMT Thr105Ile variation","entity_type_key":"cellular_process"},"role":"subject","stoichiometry":null,"state_label":"","sequence_order":0,"notes":""},{"entity":{"id":"470c158d-c9b9-5b79-b743-771272e353e8","slug":"hnmt","display_name":"Human histamine N-methyltransferase / HNMT","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":"847daefd-ce13-541a-b426-919975168a3d","slug":"histamine","display_name":"Histamine","entity_type_key":"small_molecule"},"role":"context_participant","stoichiometry":null,"state_label":"","sequence_order":3,"notes":""},{"entity":{"id":"825f2da2-01bc-5874-a3c6-64f5ac867db5","slug":"s-adenosylmethionine","display_name":"S-Adenosyl-L-methionine","entity_type_key":"small_molecule"},"role":"context_participant","stoichiometry":null,"state_label":"","sequence_order":4,"notes":""}]},"contexts":[{"dimension":"evidence_access","value_text":"Primary abstract","comparator":null,"unit":null,"notes":"","entity":null},{"dimension":"experimental_model","value_text":"Human recombinant enzyme comparison.","comparator":null,"unit":null,"notes":"","entity":null},{"dimension":"limitations","value_text":"Results paragraph reports increased Km; the abstract conclusion says lowered Km. Numerical results are retained as a source wording discrepancy, not two independent experiments. No clinical symptom prediction.","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":"A common enzyme variant changed the measured reaction kinetics.","comparator":null,"unit":null,"notes":"","entity":null},{"dimension":"primary_references","value_text":"Two polymorphic forms of human histamine methyltransferase: structural, thermal, and kinetic comparisons. · 2001 · https://pubmed.ncbi.nlm.nih.gov/11566133/ · DOI 10.1016/s0969-2126(01)00643-8","comparator":null,"unit":null,"notes":"","entity":null}],"evidence":[{"id":"1a587495-c2cd-515d-8f70-3f7e1f26cd44","evidence_kind":"source_excerpt","locator":"Lines 218-224","start_line":218,"end_line":224,"excerpt":"## histidine-hnmt-variant\nA common enzyme variant changed the measured reaction kinetics.\nRecombinant Ile105 HNMT had about 16 percent lower specific activity and higher apparent Km for SAM and histamine than Thr105 across 25-45 degrees C.\nModel: Human recombinant enzyme comparison.\nLimitations: Results paragraph reports increased Km; the abstract conclusion says lowered Km. Numerical results are retained as a source wording discrepancy, not two independent experiments. No clinical symptom prediction.\nEvidence access: Primary abstract\nTwo polymorphic forms of human histamine methyltransferase: structural, thermal, and kinetic comparisons. · 2001 · https://pubmed.ncbi.nlm.nih.gov/11566133/ · DOI 10.1016/s0969-2126(01)00643-8","model_system":"Human recombinant enzyme comparison.","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. Not publisher full text.","file_path":"","sha256":"cb672530ec8b4a4542d0f3957e80ca76bb0449e9f988845b0f7681f623c4ec9b","revision_id":"19a7f26c-d9a1-5411-a81d-025f3d98a452","review_status":"unverified_draft","notes":""}}],"relations":[],"conflicts":[],"corrections":[],"research":null}