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topical membership is not evidence of a direct dietary effect.\nplain_language: Complex II couples a B2-derived flavin with separate iron-sulfur centers.\norganism: Homo sapiens\ntissue_or_cell_type: HEK293F-derived purified complex II\nexperimental_model: Human complex II purified from HEK293F cells, cryo-EM, EPR and succinate-quinone activity assays.\nlimitations: Structural co-dependence does not show that B2 corrects iron deficiency or that iron supplementation improves this reaction.\nexposure: No nutrient intervention; structural or biochemical characterization.\ncross_nutrient: B2-derived FAD and iron-containing redox centers cooperate within one respiratory complex.\nevidence_spans: [{\"source_bundle\": \"artifacts/riboflavin_metabolism_sources.json\", \"source_key\": \"PMC10161127\", \"locator\": \"XML .//body//p\", \"paragraph_index\": 2, \"char_start\": 0, \"char_end\": 1105, \"evidence_access\": \"full-text\"}]\n[du-2023-human-complex-ii] Structure of the human respiratory complex II (2023). https://pubmed.ncbi.nlm.nih.gov/37098072/ DOI: 10.1073/pnas.2216713120","model_system":"Human complex II purified from HEK293F cells, cryo-EM, EPR and succinate-quinone activity assays.","directness":"author_interpretation","verification_status":"source_derived_draft","notes":"Exact curation-document quotation, not publisher quotation. 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