SUBSTRATE-DEPENDENT UTILIZATION OF THE GLYCEROL 3-PHOSPHATE OR MALATEASPARTATE REDOX SHUTTLES BY EHRLICH ASCITES-CELLS/

The rate of transfer of reducing equivalents from cytoplasm to mitocho ndria has been examined in Ehrlich ascites tumour cells incubated in t he presence of lactate. The flux of reducing equivalents was determine d from the rate of metabolism of reduced intermediates that are oxidiz ed within the cytosol. The magnitude of the flux of reducing equivalen ts was dependent on both the concentration of added lactate and the pr esence of carbohydrate. The rate of flux was twice as great in the pre sence of glucose and four times as high when glucose and lactate were added together as when lactate was the only added substrate. Fructose was less effective than glucose in stimulating reducing equivalent flu x. In the presence of glucose or fructose, there was a substantial acc umulation of hexose phosphates, dihydroxyacetone phosphate and glycero l 3-phosphate. Rotenone, an inhibitor of NADH dehydrogenase, and amino -oxyacetate, which inhibits the malate/aspartate shuttle, were powerfu l suppressors of reducing equivalent flux from lactate as sole substra te, but were much less potent in the presence of carbohydrate. Antimyc in substantially inhibited reducing equivalent flux from all combinati ons of added substrates, consistent with its ability to block oxidatio n of reducing equivalents transferred by both the malate/aspartate and glycerol 3-phosphate shuttles. The glycerol 3-phosphate shuttle repre sents around 80% of the maximum total observed activity but is active only while glycolytic intermediates are present to provide the necessa ry substrates of the shuttle. This Ehrlich ascites cell line has an es sentially similar total reducing equivalent shuttle capacity to that o f isolated hepatocytes.