Formation of disulfide bonds between glutathione and membrane sh groups in human erythrocytes

Abstract

In erythrocytes treated with the SH-oxidizing agent, diamide, mixed disulfide bonds between membrane proteins and GSH are formed involving 20% of the membrane SH groups. To study the distribution of these mixed disulfides over the membrane protein fractions, intracellular GSH was labelled biosynthetically with [2- 3H]glycine prior to diamide treatment of the cells and the radioactivity of defined membrane peptide fractions determined. Mixed disulfides preferentially occur in the extrinsic protein, spectrin (six SH groups), in addition to the formation of peptide disulfides. Intrinsic proteins are much less reactive: only one SH group of the major intrinsic protein (band 3) reacts with GSH, which accounts for previously observed impossibility to dimerize band 3 via disulfide bonds in intact cells. The labelling method described offers a promising strategy to label and map exposed endofacial SH groups of membrane proteins with a physiological, impermeable marker, GSH. In ghosts treated with diamide and GSH the number of mixed disulfides formed is greater than in erythrocytes. Polymerization of spectrin via intermolecular disulfide bridges is suppressed, while intramolecular disulfides are still formed, providing a means for the analysis of spectrin structure. The diamide-induced mixed membrane-GSH disulfides are readily reduced by GSH. This suggests, that GSH may also be able to reduce mixed disulfides formed in the erythrocyte membrane under oxidative stress in vivo. The reversible formation of mixed disulfides may serve to protect sensitive membrane structures against irreversible oxidative damage.