Reduction of oxaloacetate by pig liver isocitrate dehydrogenase.

Pure isocitrate dehydrogenase from pig liver cytoplasm catalyses the reduction of oxaloacetate by NADPH at a rate comparable with that observed for the usual substrates. The products are NADP and D-malate, the 'unatural' isomer. High concentrations of magnesium (25 mM) are necessary for maximal activity, and the reaction is not appreciably reversible. These results are discussed in connection with the inhibition of the enzyme by mixtures of glyoxylate and oxaloacetate. The reduction is not thought to be of physiological importance.