Oxidation of glutathione by the myeloperoxidase system.

Oxidation of glutathione (GSH) by the myeloperoxidase (MPO) system was studied. The combination of MPO, H2O2, and a halide ion oxidized GSH. This occurred at a H2O2 concentration too low to oxidize GSH by itself. The MPO-mediated oxidation of GSH required the simultaneous presence of MPO, H2O2, and a halide ion. The system had an acid pH optimum of pH 5.5-6.0. Iodide was more effective than bromide which in turn was more effective than chloride. The oxidative product was shown to be GSSG, since it could be reduced back to GSH by glutathione reductase and NADPH. The MPO-mediated oxidation of GSH may be one mechanism by which this system damages microorganisms.