Cadmium, methylmercury, mercury, and lead inhibition of calf liver glutathione S-transferase exhibiting selenium-independent glutathione peroxidase activity

Abstract

Non-selenium glutathione peroxidase was isolated from calf liver to approximately 70% of purity (by analytical and sodiumdodecyl sulfate-gel electrophoresis) by a simple purification procedure. The preparation had a specific activity of 74 units/mg with 1-chloro-2,4-dinitrobenzene (CDNB) as substrate and 14 units/mg with cumene hydroperoxide (COP). Both the peroxidase and transferase activities of the enzyme were markedly inhibited by cadmium, methylmercury, mercury, and lead. Of the various metal ions tested, cadmium was the most potent inhibitor. The nature of the inhibition of the transferase activity by metal ions was noncompetitive with respect to glutathione and CDNB. The peroxidase activity also was inhibited noncompetitively with respect to glutathione and COP. The inhibition constants (Ki) for cadmium, methylmercury, mercury, and lead were calculated to be 2, 4, 6.5, and 9 × 10-5 m, respectively, for the transferase activity and 1.5, 7, 9, and 3 × 10-6 m, respectively, for the peroxidase activity. These findings suggest that metal ion-induced lipid peroxidation may be mediated in part via inhibition of non-selenium glutathione peroxidase activity. In addition, metal ion toxicity may be expressed in part through inhibition of glutathione transferase activity which plays an important role in the detoxification of a broad spectrum of compounds. © 1981.