Cosubstrates involved in the reduction of cytosolic glutathione disulfide in rat heart.
The functionality of glutathione (GSH), which is present in separate mitochondrial and cytosolic pools, hinges on a steady supply of reducing equivalents, provided by NADPH, to convert glutathione disulfide (GSSG) to GSH. It is believed traditionally that glucose 6-phosphate (G6-P) via the pentose phosphate pathway is the main cellular source of NADPH. The current study examined the ability of NADH- and NADPH-linked cosubstrates to support cardiac cytosolic GSSG reduction. Exogenous NADP+ was added to the incubation mixtures because of the loss of this nucleotide during homogenization. Exogenous GSSG was added to all samples to levels that were approximately 60% of total glutathione. In both the 500 x g (with mitochondria) and 10,000 x g (without mitochondria) rat heart supernatants, isocitrate supported reduction of approximately 90% of available GSSG within 10 min. Malate, pyruvate and palmitoyl carnitine did not support GSSG reduction in either supernatant. G6-P yielded 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 data indicate: (1) The pentose phosphate pathway, alone, is less efficient than isocitrate at supplying reducing equivalents for cytosolic GSSG reduction; and (2) some confounding factor(s) occur in the 500 x g and reconstituted 500 x g supernatants whereby G6-P-supported GSSG reduction is attenuated.
Robertson
J D
JD
Division of Pharmacology and Toxicology, College of Pharmacy, The University of Texas at Austin, 78712-1074, USA. jdrobertson@mail.utexas.edu
Starnes
J W
JW
Kehrer
J P
JP
D000818:Animals; D003600:Cytosol / Q000378:metabolism; D019298:Glucose-6-Phosphate / Q000378:metabolism; D019803:Glutathione Disulfide / Q000378:metabolism*; D008297:Male; D009206:Myocardium / Q000378:metabolism*; D009249:NADP / Q000032:analysis; D010084:Oxidation-Reduction; D010427:Pentose Phosphate Pathway; D051381:Rats; D017207:Rats, Sprague-Dawley
D009249:NADP; D019298:Glucose-6-Phosphate; D019803:Glutathione Disulfide