A role of mitochondrial glutathione peroxidase in modulating mitochondrial oxidations in liver.

Abstract

1 The inhibitory effect of t-butyl hydroperoxide on O2 uptake by perfused rat liver and by isolated hepatocytes was investigated with isolated mitochondria. 2 O2 uptake by mitochondria oxidizing the ketoacids, 2-oxoglutarate and pyruvate, was substantially decreased upon addition of t-butyl hydroperoxide, that of isocitrate was only slightly decreased, and that of succinate and of 3-hydroxybutyrate was practically unchanged. The reduction product of the hydroperoxide, t-butyl alcohol, showed no effect. The inhibitory effect of the hydroperoxide was reversed upon addition of dithioerythritol, a thiol reductant. The inhibitory effect of the hydroperoxide was mimicked by the penetrant disulfide, cystamine, and by the thiol-oxidizing agent, diamide. 3 Mitochondrial extracts from rats fed a selenium-deficient diet were shown to have virtually no measurable GSH peroxidase activity. The hydroperoxide had almost no inhibitory effect on 2-oxoglutarate-dependent O2 uptake in mitochondria from selenium-deficient rats. 4 These observations demonstrate effects of GSH peroxidase activity in the mitochondrial matrix on the pattern of substrate oxidations, possibly with the ketoacid oxidases, dependent on coenzyme A and lipoamide, as main target sites. In view of the known steady-state formation of mitochondrial O2− and H2O2, a connection between the resulting oxidation of mitochondrial GSH and NADPH and the regulation of mitochondrial substrate oxidations is proposed.