Acid-volatile selenium formation catalyzed by glutathione reductase.

The production of acid-volatile selenide (apparently H2Se) was catalyzed by glutathione reductase in an anaerobic system containing 20 mM glutathione, 0.05 mM sodium selenite, a TPNH-generating system, and microgram quantities of highly purified yeast glutathione reductase. H2Se production in this system was proportional to glutathione reductase concentration and was maximal at pH 7. Significant nonenzymic H2Se production occurred in the system lacking glutathione reductase and TNPH. A concentration of arsenite (0.1 mM) which does not inhibit glutathione reductase inhibited selenide volatilization, as did bovine serum albumin (1.67 mg/ml). Both appear to inhibit Se volatilization by reacting with the selenide product(s). The selenotrisulfide derivative of glutathione (GSSeSG) was readily converted to H2Se by glutathione reductase and TPNH without the addition of glutathione. These results suggest that GSSeSG formed nonenzymically from glutathione and selenic undergoes stepwise reduction by glutathione reductase (or excess GSH) to GSSeH and finally to H2Se. The same pathway operates when glutathione is used as the reducing agent but to a lesser extent.