One- and two-electron oxidation of reduced glutathione by peroxidases

The oxidation of glutathione by horseradish peroxidase or lactoperoxidase forms a thiyl free radical, as demonstrated with the spin-trapping ESR technique. Reactions of this thiyl free radical result in oxygen consumption, which is inhibited by the radical trap 5,5-dimethyl-1-pyrroline-N-oxide. In contrast to L-cysteine oxidation, glutathione oxidation is highly hydrogen peroxide-dependent. The oxidation of glutathione by glutathione peroxidase forms GSSG without forming a thiyl radical intermediate except in the presence of the thiyl radical-generating horseradish peroxidase.