OXIDATIVE HEMOLYSIS AND PRECIPITATION OF HEMOGLOBIN. II. ROLE OF THIOLS IN OXIDANT DRUG ACTION*

Abstract

During the oxidative injury of hemoglobin in solution or in red cells, thiol groups play a key role. Whether oxidation is spontaneous or accelerated by such electron-carrying compounds as phenylhydrazine, the following steps ensue (1) Reduced glutathione (GSH) is oxidized to GSSG. In being oxidized a portion of the GSH becomes bound to hemoglobin by forming mixed disulfides with the globin sulfhydryl groups. (2) Hemoglobin is converted to methemoglobin as ferroheme becomes ferriheme. (3) The two reactive sulfhydryl groups of native hemoglobin are oxidized. (4) Oxidation of these two thiol groups probably results in the loss of the normal configuration of the hemoglobin molecule with the following consequences: (a) the oxygen equilibrium (dissociation curve) is altered; (b) fast-moving components of hemoglobin, including mixed disulfides of GSH and hemoglobin, appear on electrophoresis or chromatography; (c) other reactive groups of the globin molecule, including the remaining four sulfhydryl groups, become susceptible to oxidation. (5) Brown to green hemochromes form ("sulfhemoglobin"). (6) Denatured hemoglobin molecules polymerize, probably by hydrogen bonding, and precipitate to form coccoid granules (Heinz bodies). Glutathione buffers hemoglobin against oxidation and may protect globin sulfhydryls by formation of mixed disulfides. As a result, GSH slows the precipitation of hemoglobin so that fewer, larger Heinz bodies are formed. Probably GSH provides similar protection to other oxidatively labile constituents of the red cell such as the sulfhydryl groups of its enzymes and of its membrane. Presumably, injury to these latter components accounts for the actual hemolysis in vivo and for the spherocytosis observed in vitro.