Properties of glutathione release observed during reduction of organic hydroperoxide, demethylation of aminopyrine and oxidation of some substances in perfused rat liver, and their implications for the physiological function of catalase.
The enhanced reduction of t-butyl hydroperoxide by glutathione peroxidase is accompanied by a decrease in the cellular concentration of both glutathione and NADPH in isolated liver cells, resulting in the release of GSSG (oxidized glutathione) from the perfused rat liver. This phenomenon, first reported by H. Sies, C. Gerstenecker, H. Menzel & L. Flohé (1972) (FEBS Lett. 27, 171-175), can be observed under a variety of conditions, not only with the acceleration of the glutathione peroxidase reaction by organic peroxides, but also during the oxidation of glycollate and benzylamine, during demethylation of aminopyrine in the liver of the phenobarbital-pretreated rat and during oxidation of uric acid in the liver of the starved rat pretreated with 3-amino-1,2,4-triazole. The rate of release of GSSG is altered markedly by changes in the metabolic conditions which affect the rate of hepatic NADPH generation. Thus, regardless of whether achieved by enhanced oxidation of glutathione by glutathione peroxidase or by oxidation of NADPH through other metabolic pathways, an increase in the cellular concentration of GSSG appears to facilitate its release. It has been found that, in addition to the hexose monophosphate shunt, the mitochondrial NADH-NADP+ transhydrogenase reaction plays an important role in supplying reducing equivalents to the glutathione peroxidase reaction and in maintaining the cellular oxidation-reduction state of the nicotinamide nucleotides. Spectrophotometric analysis of the steady-state concentration of the catalase-H2O2 intermediate with simultaneous measurement of the rate of release of GSSG leads to the conclusion that intracellular compartmentation of catalase in the peroxisomes and glutathione peroxidase in the cytosol and mitochondria distinguishes the reactivities of these enzymes one from the other, and facilitates their effective cooperation in hydroperoxide metabolism in the liver.