Sensitivity of Hemoglobin Thiol Groups within Red Blood Cells of Rat during Oxidation of Glutathione

The intracellular thiol-oxidising diazenes, diazenedicarboxylic acid bis-N,N-dimethylamide and diazenedicarboxylic acid bis-N'-ethylpiperazinide, have been used in the study of red cells. A difference in the consequences of diazene oxidant treatment between the human red cell and rat red cells has been found in respect to the quantity of oxidant needed for glutathione (GSH) oxidation, to the fate of GSH, and to the reactivity of hemoglobin. In the first place, significantly more oxidant is needed for GSH oxidation in the rat red cell than in the human cell. Secondly, in the human cell, all of the GSH is converted to glutathione disulfide (GSSG), from which GSH is regenerated. In the rat cell, GSH disappears without being converted to GSSG, and GSH is not regenerated. Thirdly, a decrease in rat hemoglobin thiol groups, but no change in human hemoglobin, is found. Sterically unhindered thiol groups in the rat hemoglobin are thought to react with the usual adduct intermediate in GSH oxidation by diazene (formed from RCON = NCOR + GSH leads to RCON(SG)NHCOR) to produce mixed disulfides, from which GSH is not easily regenerated. The results support the idea that reduction of mixed disulfides of GSH and protein is not carried out directly by GSSG reductase but necessitates thiol transferase and GSH. The thiol-oxidising diazenes may be of use in mapping of exposed, reactive thiol groups in proteins.