title: Calcium and 2-oxoglutarate-mediated control of aspartate formation by rat heart mitochondria.
abstract: Studies of the influence of calcium on the metabolism of cardiac mitochondria have indicated that calcium activates key enzymes involved in the citric acid cycle. Calcium-mediated activation of one of these enzymes, 2-oxoglutarate dehydrogenase, has been shown to cause a marked decrease in the steady-state concentration of 2-oxoglutarate in both heart and liver mitochondria. In liver, 2-oxoglutarate is a potent inhibitor of oxalacetate transamination to aspartate and activation of this enzyme by calcium-mobilizing hormones leads to a stimulation of aspartate formation and gluconeogenesis. Since mitochondrial aspartate formation is a key step in the malate/aspartate shuttle, we investigated the control of aspartate formation by cardiac mitochondria. In mitochondria incubated with glutamate and malate, activation of 2-oxoglutarate dehydrogenase by calcium led to an inhibition of aspartate formation. However, calcium caused a stimulation of aspartate production when incubations were supplemented with pyruvate as an additional substrate. Estimates of the mitochondrial redox potential (NADH/NAD+) indicated that both calcium and pyruvate increased the redox potential. The observed influence of calcium on aspartate formation was found to be due to a balance between is inhibitory effect, caused by an increased redox potential, and its stimulatory effect, caused by a decreased 2-oxoglutarate concentration. Under conditions in which the redox component was held constant, a kinetic analysis indicated that the apparent Ki for 2-oxoglutarate inhibition of aspartate formation is 0.2 mM. The data suggest that activation of cardiac 2-oxoglutarate dehydrogenase by calcium could lead to stimulation of the mitochondrial oxidation of cytosolic NADH via the malate/aspartate cycle.
authors.affiliation: Department of Cellular and Molecular Physiology, Milton S. Hershey Medical Center, Pennsylvania State University, Hershey 17033.
authors.forename: R C
authors.initials: RC
authors.lastname: Scaduto
mesh_terms: D000818:Animals; D001224:Aspartic Acid / Q000096:biosynthesis*; D002118:Calcium / Q000494:pharmacology*; D004140:Dinitrophenols / Q000494:pharmacology; D004789:Enzyme Activation / Q000187:drug effects; D005971:Glutamates / Q000378:metabolism; D018698:Glutamic Acid; D007655:Ketoglutarate Dehydrogenase Complex / Q000187:drug effects / Q000378:metabolism*; D007656:Ketoglutaric Acids / Q000494:pharmacology*; D008293:Malates / Q000378:metabolism; D008564:Membrane Potentials; D008929:Mitochondria, Heart / Q000378:metabolism*; D008954:Models, Biological; D009243:NAD / Q000378:metabolism; D011773:Pyruvates / Q000378:metabolism; D019289:Pyruvic Acid; D051381:Rats
chemical_list: D004140:Dinitrophenols; D005971:Glutamates; D007656:Ketoglutaric Acids; D008293:Malates; D011773:Pyruvates; D009243:NAD; D001224:Aspartic Acid; D018698:Glutamic Acid; C030298:malic acid; D019289:Pyruvic Acid; D007655:Ketoglutarate Dehydrogenase Complex; D002118:Calcium