?-Hemoglobin stabilizing protein (AHSP) markedly decreases the redox potential and reactivity of ?-subunits of human HbA with hydrogen peroxide.

ABSTRACT: ?-Hemoglobin stabilizing protein (AHSP) is a molecular chaperone that binds monomeric ?-subunits of human hemoglobin A (HbA) and modulates heme iron oxidation and subunit folding states. Although AHSP·?Hb complexes autoxidize more rapidly than HbA, the redox mechanisms appear to be similar. Both metHbA and isolated met-?-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-?-subunits as compared with met-?-subunits, and no ferryl heme is detected in H(2)O(2)-treated AHSP·met-?-complex at pH values from 5.0 to 9.0 at 23 °C. Ferryl heme species were similarly not detected in AHSP·met-? 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 ?- and ?-subunits. In contrast, treatment of free ?-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·?-complexes. AHSP binding also dramatically reduces the redox potential of ?-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) ?-subunits. Hexacoordination in the AHSP·met-? complex markedly decreases the rate of the initial H(2)O(2) reaction with iron and thus provides ?-subunits protection against damaging oxidative reactions.

SUBMITTER: Mollan TL 

PROVIDER: S-EPMC3567680 | biostudies-literature | 2013 Feb

REPOSITORIES: biostudies-literature