title: Warfarin modulates the nitrite reductase activity of ferrous human serum heme-albumin.
abstract: Human serum heme-albumin (HSA-heme-Fe) displays reactivity and spectroscopic properties similar to those of heme proteins. Here, the nitrite reductase activity of ferrous HSA-heme-Fe [HSA-heme-Fe(II)] is reported. The value of the second-order rate constant for the reduction of [Formula: see text] to NO and the concomitant formation of nitrosylated HSA-heme-Fe(II) (i.e., k on) is 1.3 M(-1) s(-1) at pH 7.4 and 20 °C. Values of k on increase by about one order of magnitude for each pH unit decrease between pH 6.5 to 8.2, indicating that the reaction requires one proton. Warfarin inhibits the HSA-heme-Fe(II) reductase activity, highlighting the allosteric linkage between the heme binding site [also named the fatty acid (FA) binding site 1; FA1] and the drug-binding cleft FA2. The dissociation equilibrium constant for warfarin binding to HSA-heme-Fe(II) is (3.1 ± 0.4) × 10(-4) M at pH 7.4 and 20 °C. These results: (1) represent the first evidence for the [Formula: see text] reductase activity of HSA-heme-Fe(II), (2) highlight the role of drugs (e.g., warfarin) in modulating HSA(-heme-Fe) functions, and (3) strongly support the view that HSA acts not only as a heme carrier but also displays transient heme-based reactivity.
authors.affiliation: Interdepartmental Laboratory of Electron Microscopy, University Roma Tre, Via della Vasca Navale 79, 00146, Rome, Italy, ascenzi@uniroma3.it.
authors.forename: Paolo
authors.initials: P
authors.lastname: Ascenzi
authors.forename: Grazia R
authors.initials: GR
authors.lastname: Tundo
authors.forename: Gabriella
authors.initials: G
authors.lastname: Fanali
authors.forename: Massimo
authors.initials: M
authors.lastname: Coletta
authors.forename: Mauro
authors.initials: M
authors.lastname: Fasano
mesh_terms: D000494:Allosteric Regulation / Q000187:drug effects; D000925:Anticoagulants / Q000494:pharmacology*; D005296:Ferrous Compounds / Q000737:chemistry / Q000378:metabolism*; D006418:Heme / Q000737:chemistry / Q000378:metabolism*; D006801:Humans; D009572:Nitrite Reductases / Q000378:metabolism*; D012709:Serum Albumin / Q000737:chemistry / Q000378:metabolism*; D014859:Warfarin / Q000494:pharmacology*
chemical_list: D000925:Anticoagulants; D005296:Ferrous Compounds; D012709:Serum Albumin; D006418:Heme; D014859:Warfarin; D009572:Nitrite Reductases
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