Thiol-induced hemoglobin oxidation

Summary

Addition of cysteine in the mM range to purified oxyhemoglobin, red blood cell lysate or red blood cell suspensions leads to oxidation of the hemoprotein. The rate and extent of the process depend on the initial hemoglobin and cysteine concentrations, and the reaction is limited by the total destruction of the sulfhydryl groups. Similar results are obtained employing glutathione, but the rate of the process is considerably slower. Oxidation of the purified hemoprotein is faster than in the red blood cell lysate. This difference is mainly due to the inhibitory effect of catalase present in the lysate. Addition of sodium azide increases the rate of oxyhemoglobin oxidation in the lysate, while addition of catalase reduces the rate of oxidation of the purified hemoprotein. The results are interpreted in terms of a mechanism comprising the oxidation of the oxyhemoglobin by the -SH group, with concomitant formation of superoxide anion and hydrogen peroxide. These species further contribute to the oxyhemoglobin oxidation. A chain oxidation of the thiol, catalyzed by the hemoprotein, explains the extensive cysteine destruction.