{"id":"15345586-c9b8-55d8-84a0-20204d95e1ec","stable_key":"548ab9d6-3a9b-5bed-879c-17d03813b636:b2-txnrd-sec498cys-turnover","predicate":"reduces-activity-toward","statement":"Replacing rat TXNRD1 Sec498 with cysteine lowered thioredoxin-reduction kcat about 100-fold; serine substitution and terminal truncation lacked detectable activity.","claim_class":"mechanistic","status":"source_derived_draft","evidence_grade":"ungraded","direction":"negative","is_public":true,"mechanism_event_id":"8a89bf33-9e82-5afb-8168-c760a788b402","mechanism_event_label":"Flavin retention did not preserve efficient thioredoxin reduction.","subject":{"id":"3e52ad46-1a6e-52c4-b5d6-fda4a32b8725","slug":"rat-txnrd1-sec498cys","display_name":"Rat TXNRD1 Sec498Cys protein","entity_type_key":"protein_state"},"object":{"id":"8067bcb1-798d-5248-9e23-9ab8b107a960","slug":"thioredoxin-proteins","display_name":"Thioredoxin proteins","entity_type_key":"protein_family"},"evidence_count":1,"mechanism_event":{"id":"8a89bf33-9e82-5afb-8168-c760a788b402","stable_key":"548ab9d6-3a9b-5bed-879c-17d03813b636:b2-txnrd-sec498cys-turnover-event","event_type":"biochemical_relationship","label":"Flavin retention did not preserve efficient thioredoxin reduction.","description":"Replacing rat TXNRD1 Sec498 with cysteine lowered thioredoxin-reduction kcat about 100-fold; serine substitution and terminal truncation lacked detectable activity.","status":"provisional","compartment":null,"participants":[{"entity":{"id":"8067bcb1-798d-5248-9e23-9ab8b107a960","slug":"thioredoxin-proteins","display_name":"Thioredoxin proteins","entity_type_key":"protein_family"},"role":"assay substrate; species not established by the accessible abstract","stoichiometry":null,"state_label":"","sequence_order":0,"notes":""},{"entity":{"id":"e2cd7179-f218-54e8-9ce9-7a836ae35fac","slug":"fad","display_name":"FAD","entity_type_key":"small_molecule"},"role":"retained upstream cofactor","stoichiometry":null,"state_label":"","sequence_order":1,"notes":""},{"entity":{"id":"dc89d7e2-8f89-577b-838f-42bf5d8ec7c8","slug":"selenium","display_name":"Selenium","entity_type_key":"nutrient_element"},"role":"present in wild-type selenocysteine; removed by substitution","stoichiometry":null,"state_label":"","sequence_order":2,"notes":""},{"entity":{"id":"3e52ad46-1a6e-52c4-b5d6-fda4a32b8725","slug":"rat-txnrd1-sec498cys","display_name":"Rat TXNRD1 Sec498Cys protein","entity_type_key":"protein_state"},"role":"subject","stoichiometry":null,"state_label":"","sequence_order":3,"notes":""}]},"contexts":[{"dimension":"availability_state","value_text":"machinery_impairment","comparator":null,"unit":null,"notes":"Imported condition classification; unverified.","entity":null},{"dimension":"cross_nutrient","value_text":"B2-derived FAD cannot replace the selenium-containing catalytic residue.","comparator":null,"unit":null,"notes":"","entity":null},{"dimension":"evidence_location","value_text":"Abstract","comparator":null,"unit":null,"notes":"","entity":null},{"dimension":"experimental_model","value_text":"Rat TXNRD1 Sec498Cys, Sec498Ser and C-terminal truncation expressed in E. coli; FAD analysis, NADPH titration and thioredoxin assays.","comparator":null,"unit":null,"notes":"","entity":null},{"dimension":"exposure","value_text":"Purified-enzyme assay","comparator":null,"unit":null,"notes":"","entity":null},{"dimension":"limitations","value_text":"Assay-substrate species is unresolved in accessible source details; engineered proteins do not establish dietary B2-by-selenium synergy.","comparator":null,"unit":null,"notes":"","entity":null},{"dimension":"nutrient_topic","value_text":"Riboflavin research collection; topical membership is not evidence of a direct dietary effect.","comparator":null,"unit":null,"notes":"","entity":{"slug":"riboflavin","display_name":"Riboflavin (vitamin B2)","entity_type_key":"small_molecule"}},{"dimension":"organism","value_text":"Rattus norvegicus protein expressed in Escherichia coli","comparator":null,"unit":null,"notes":"","entity":null},{"dimension":"plain_language","value_text":"Flavin retention did not preserve efficient thioredoxin reduction.","comparator":null,"unit":null,"notes":"","entity":null},{"dimension":"primary_references","value_text":"[zhong2000] Essential role of selenium in the catalytic activities of mammalian thioredoxin reductase revealed by characterization of recombinant enzymes with selenocysteine mutations. (2000). https://pubmed.ncbi.nlm.nih.gov/10849437/ DOI: 10.1074/jbc.m000690200","comparator":null,"unit":null,"notes":"","entity":null},{"dimension":"tissue_or_cell_type","value_text":"Purified recombinant enzyme; no intact tissue","comparator":null,"unit":null,"notes":"","entity":null},{"dimension":"trigger_kind","value_text":"machinery_impairment","comparator":null,"unit":null,"notes":"Imported condition classification; unverified.","entity":null}],"evidence":[{"id":"a49fe1bb-4ecf-5bc5-86ae-3f23a1c5b362","evidence_kind":"source_excerpt","locator":"Lines 1388-1400","start_line":1388,"end_line":1400,"excerpt":"### b2-txnrd-sec498cys-turnover\nReplacing rat TXNRD1 Sec498 with cysteine lowered thioredoxin-reduction kcat about 100-fold; serine substitution and terminal truncation lacked detectable activity.\nCondition category: machinery_impairment\nnutrient_topic: Riboflavin research collection; topical membership is not evidence of a direct dietary effect.\nplain_language: Flavin retention did not preserve efficient thioredoxin reduction.\norganism: Rattus norvegicus protein expressed in Escherichia coli\ntissue_or_cell_type: Purified recombinant enzyme; no intact tissue\nexperimental_model: Rat TXNRD1 Sec498Cys, Sec498Ser and C-terminal truncation expressed in E. coli; FAD analysis, NADPH titration and thioredoxin assays.\nlimitations: Assay-substrate species is unresolved in accessible source details; engineered proteins do not establish dietary B2-by-selenium synergy.\nexposure: Purified-enzyme assay\ncross_nutrient: B2-derived FAD cannot replace the selenium-containing catalytic residue.\nevidence_location: Abstract\n[zhong2000] Essential role of selenium in the catalytic activities of mammalian thioredoxin reductase revealed by characterization of recombinant enzymes with selenocysteine mutations. 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