title: α-Hemoglobin stabilizing protein (AHSP) markedly decreases the redox potential and reactivity of α-subunits of human HbA with hydrogen peroxide.
abstract: α-Hemoglobin stabilizing protein (AHSP) is a molecular chaperone that binds monomeric α-subunits of human hemoglobin A (HbA) and modulates heme iron oxidation and subunit folding states. Although AHSP·αHb complexes autoxidize more rapidly than HbA, the redox mechanisms appear to be similar. Both metHbA and isolated met-β-subunits undergo further oxidation in the presence of hydrogen peroxide (H(2)O(2)) to form ferryl heme species. Surprisingly, much lower levels of H(2)O(2)-induced ferryl heme are produced by free met-α-subunits as compared with met-β-subunits, and no ferryl heme is detected in H(2)O(2)-treated AHSP·met-α-complex at pH values from 5.0 to 9.0 at 23 °C. Ferryl heme species were similarly not detected in AHSP·met-α Pro-30 mutants known to exhibit different rates of autoxidation and hemin loss. EPR data suggest that protein-based radicals associated with the ferryl oxidation state exist within HbA α- and β-subunits. In contrast, treatment of free α-subunits with H(2)O(2) yields much smaller radical signals, and no radicals are detected when H(2)O(2) is added to AHSP·α-complexes. AHSP binding also dramatically reduces the redox potential of α-subunits, from +40 to -78 mV in 1 m glycine buffer, pH 6.0, at 8 °C, demonstrating independently that AHSP has a much higher affinity for Fe(III) versus Fe(II) α-subunits. Hexacoordination in the AHSP·met-α complex markedly decreases the rate of the initial H(2)O(2) reaction with iron and thus provides α-subunits protection against damaging oxidative reactions.
authors.affiliation: Laboratory of Biochemistry and Vascular Biology, Division of Hematology, Center for Biologics Evaluation and Research, Food and Drug Administration, Bethesda, Maryland 20852, USA.
authors.forename: Todd L
authors.initials: TL
authors.lastname: Mollan
authors.forename: Sambuddha
authors.initials: S
authors.lastname: Banerjee
authors.forename: Gang
authors.initials: G
authors.lastname: Wu
authors.forename: Claire J
authors.initials: CJ
authors.lastname: Parker Siburt
authors.forename: Ah-Lim
authors.initials: AL
authors.lastname: Tsai
authors.forename: John S
authors.initials: JS
authors.lastname: Olson
authors.forename: Mitchell J
authors.initials: MJ
authors.lastname: Weiss
authors.forename: Alvin L
authors.initials: AL
authors.lastname: Crumbliss
authors.forename: Abdu I
authors.initials: AI
authors.lastname: Alayash
mesh_terms: D001798:Blood Proteins / Q000737:chemistry* / Q000378:metabolism; D006441:Hemoglobin A / Q000737:chemistry* / Q000378:metabolism; D006801:Humans; D006861:Hydrogen Peroxide / Q000737:chemistry* / Q000494:pharmacology; D006863:Hydrogen-Ion Concentration; D008706:Methemoglobin / Q000737:chemistry* / Q000378:metabolism; D018832:Molecular Chaperones / Q000737:chemistry* / Q000378:metabolism; D046912:Multiprotein Complexes / Q000737:chemistry* / Q000378:metabolism; D016877:Oxidants / Q000737:chemistry / Q000494:pharmacology; D010084:Oxidation-Reduction / Q000187:drug effects
chemical_list: C468768:AHSP protein, human; D001798:Blood Proteins; D018832:Molecular Chaperones; D046912:Multiprotein Complexes; D016877:Oxidants; D008706:Methemoglobin; D006441:Hemoglobin A; D006861:Hydrogen Peroxide