High resolution

Module 2: Figure GSH/GSSG couple

The GSH/GSSG redox couple.

GSH is a tripeptide consisting of glutamic acid, cysteine and glycine. In its oxidized state, two molecules of GSH are joined together through a disulphide bond to form GSSG. This is the most abundant redox couple in the cell. The state of this couple can be determined by measuring the half-cell reduction potential (E-hc). Under normal reducing conditions, this potential is high, i.e.–240 mV, and this seems to be associated with cell proliferation. Differentiation seems to occur at lower potentials (−200 mV), whereas still lower potentials of −170 mV favour apoptosis. At these lower potentials, where there is an alteration in the redox balance, the build-up of GSSG within the cell can reverse the operation of the glutaredoxin system that functions normally in the recovery of oxidation-sensitive processes. GSSG interacts with reduced glutaredoxin [Grx-(SH)2] to form oxidized Grx-S2, and this disulphide bond can be transferred to oxidize target proteins.