Factors influencing the autoxidation of hemoglobin A.

Autoxidation of hemoglobin A incubated at 20°or 37°over a period of 24 hr was affected by several factors. Oxidation of oxyhemoglobin (HbO2) and deoxyhemoglobin (DeoxyHb) was faster as the pH value decreased. Allosteric effectors (IHP and EDTA) and reducing agents (ascorbic acid and cysteine) promoted the proton-assisted oxidation of HbO2 to produce methemoglobin (MetHb) and/or precipitates. Metal ions (Fe2+, Fe3+, Cu2+ and Hg2+) had a stimulatory effect at pH 7 and 5.5 on the production of MetHb or precipitates from both HbO2 and DeoxyHb. The Cu2+-and Hg2+-catalyzed oxidations of HbO2 were dramatically suppressed by EDTA, while those catalyzed by Fe2+ and Fe3+ were accelerated by EDTA. The Fe2+ (and Fe3+)-EDTA complexes were potent inducers of the oxidation in the presence of oxygen, while EDTA blocked the Fe2+-catalyzed oxidation of DeoxyHb. The oxidations catalyzed by all these metal ions were suppressed by ascorbic acid and cysteine. The Fe2+ (and Fe3+)-ascorbate (and cysteine) complexes effectively deoxygenated HbO2.