PROTEIN S-THIOLATION AND REDOX REGULATION OF MEMBRANE-BOUND GLUTATHIONE TRANSFERASE

Membrane-bound GST transferase (GSTm) occurs in hepatic microsomal and plasma membranes as well as in the outer mitochondrial membrane, and it is known to be activated by N-ethylmaleimide. We recently analysed the activation by GSSG in some detail. The approximate to 5-fold stimu lation is reversed upon reduction of GSSG by GSSG reductase. In steady -state experiments, the K-ox value was determined to be 0.05, i.e. 20 times more GSSG than GSH produces half-maximal activation. K-ox is ind ependent of the total glutathione concentration, indicating that S-thi olation by mixed disulfide formation, rather than interchain or intrac hain disulfide bridge formation, is responsible for activation. In Wes tern blots, a 17.7 kDa band, in addition to the 17.3 kDa band, was det ected upon treatment with GSSG or with GSH plus t-butyl hydroperoxide. We suggest that under oxidative stress, GSTm is activated through dir ect S-thiolation of the enzyme. Dethiolation occurs via thiol disulfid e exchange governed by the cellular glutathione redox state. (C) 1998 Elsevier Science Ireland Ltd. All rights reserved.