Oxidation of reduced nicotinamide-adenine dinucleotide by the malate- -aspartate shuttle in ehrlich ascites tumour cells.

Abstract The capability of ascites tumour mitochondria to oxidize externally formed NADH has been investigated in intact cells. Lactate has been used as the source of reducing equivalents and the oxidation of this substrate to pyruvate has been estimated. Ascites cells, under conditions of endogenous metabolism, are able to produce pyruvate upon addition of lactate. This effect is prevented by aminooxyacetate, an inhibitor of glutamate—oxalacetate transaminase (EC 2.6.1.1). Half-maximal inhibition by aminooxyacetate is attained at a concentration of approx. 30 μM. Oxidation of lactate is also sensitive to inhibitors of mitochondrial electron and energy transfer and it is enhanced by α-oxoglutarate plus aspartate. These data demonstrate that reducing equivalents can be transported across the mitochondrial membrane of intact Ehrlich ascites tumour cells by the malate—aspartate shuttle.