THE REACTION OF SUPEROXIDE WITH REDUCED GLUTATHIONE

Superoxide, generated by a xanthine oxidase/hypoxanthine system, react s with reduced glutathione (GSH) to cause an increase in oxygen consum ption and oxidized glutathione (GSSG) formation, both of which are ful ly inhibited by superoxide dismutase. In this study we have shown that little, if any, of the additional oxygen consumed is converted to hyd rogen peroxide. We have confirmed that approximately 90% of the GSH is oxidized to GSSG, the remainder being converted to the sulfonic acid. Approximately 1.2 mol of GSSG was formed for each additional mole of oxygen consumed in the presence of GSH. The efficiency of the reaction increased with increasing GSH concentration (1-8 mM), pH, and pO(2) a nd with decreasing superoxide generation rate. The results are consist ent with a superoxide-dependent chain that does not produce hydrogen p eroxide and that is terminated primarily by superoxide dismutation. We propose that this occurs via an initial reaction of superoxide with G SH to produce a sulfinyl radical rather than hydrogen transfer to give the thiyl radical. Our data suggest a rate constant for the superoxid e/GSH reaction in the 10(2)-10(3) M(-1) s(-1) range. GSH at the millim olar concentrations found intracellularly should react with superoxide , but because superoxide is regenerated, it mill not be an effective s cavenger. Physiologically, superoxide dismutase is required to prevent chain oxidation of GSH. (C) 1994 Academic Press, Inc.