Evidence for the oxidation of glycolytic NADH by the malate-aspartate shuttle in Ehrlich ascites tumor cells.

Actively glycolyzing Ehrlich-Lettré ascites tumor cells have been tested for their ability to reoxidize into the mitochondria reduced nicotinamide adenine dinucleotide by the malate-aspartate shuttle. The aspartate transaminase inhibitor aminooxyacetate has been used as a tool for evaluating it. Measurements of the free cytosolic $\text{(NADH)}\text{(}\text{NAD}{}^{\mathrm{+}}\text{)}$ ratio indicate that it increases gradually in the inhibitor-treated cells up to a value about ninefold higher than in the controls after 30 min of glycolytic activity. Fructose 1, 6-diphosphate and dihydroxyacetone phosphate reach a steady-state level after 5 min of incubation in the untreated cells, whereas they accumulate in large amounts in the inhibited cells. Correspondingly, a decrease in 3-phosphoglycerate concentration is observed. On the other hand, the rate of glucose utilization is affected slightly only during long observation times. From these results it may be established that in Ehrlich ascites cells reducing equivalents generated in the cytosol during aerobic glycolysis strongly influence the NAD redox state when their intramitochondrial translocation is prevented by the inactivation of the malate-aspartate shuttle.