COSUBSTRATES INVOLVED IN THE REDUCTION OF CYTOSOLIC GLUTATHIONE DISULFIDE IN RAT-HEART

The functionality of glutathione (GSH), which is present in separate m itochondrial and cytosolic pools, hinges on a steady supply of reducin g equivalents, provided by NADPH, to convert glutathione disulfide (GS SG) to GSH. It is believed traditionally that glucose 6-phosphate (G6- P) via the pentose phosphate pathway is the main cellular source of NA DPH. The current study examined the ability of NADH-and NADPH-linked c osubstrates to support cardiac cytosolic GSSG reduction. Exogenous NAD P(+) was added to the incubation mixtures because of the loss of this nucleotide during homogenization. Exogenous GSSG was added to all samp les to levels that were similar to 60% of total glutathione. In both t he 500 x g (with mitochondria) and 10 000 x g (without mitochondria) r at heart supernatants, isocitrate supported reduction of similar to 90 % of available GSSG within 10 min. Malate, pyruvate and palmitoyl carn itine did not support GSSG reduction in either supernatant. G6-P yield ed GSH levels within 10 min equal to 77% of total glutathione in the 1 0000 x g supernatant and 47% in the 500 x g supernatant. The current d ata indicate: (1) The pentose phosphate pathway, alone, is less effici ent than isocitrate at supplying reducing equivalents for cytosolic GS SG reduction; and (2) some confounding factor(s) occur in the 500 x g and reconstituted 500 x g supernatants whereby G6-P-supported GSSG red uction is attenuated. (C) 1997 Elsevier Science Ireland Ltd.