Decreases the Redox Potential and Reactivity of-Subunits of Human HbA with Hydrogen Peroxide

摘要: Background: ɑ-Hemoglobin stabilizing protein (AHSP) modifies the redox properties of bound ɑ-subunits. Results: Isolated hemoglobin subunits exhibit significantly different redox properties compared with HbA. A significant decrease in the reduction potential of ɑ-subunits bound to AHSP results in preferential binding of ferric ɑ. Conclusion: AHSPɑ-subunit complexes do not participate in ferric-ferryl heme redox cycling. Significance: AHSP binding to ɑ-subunits inhibits subunit pseudoperoxidase activity.-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 (H2O2) to form ferryl heme species. Surprisingly, much lower levels of H2O2-induced ferryl heme are produced by free met--subunits as compared with met--subunits, and no ferryl heme is detected in H2O2-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 H2O2 yields much smaller radical signals, and no radicals are detected when H2O2 is added to AHSP-complexes. AHSP binding also dramatically reduces the redox potential …