Regulation of Malate Oxidation in Isolated Mung Bean Mitochondria

Abstract

To investigate the relationship between malate oxidation and subsequent cycle reactions, the effects of oxaloacetate, pyruvate, and thiamine pyrophosphate on malate oxidation in mung bean (Phaseolus aureus cv. ''Jumbo'') hypocotyl mitochondria were quantitatively examined. Malate oxidation was optimally stimulated by addition of pyruvate and thiamine pyrophosphate, whose addition lowered the apparent Km for malate from 5 mM to 0.1 mM. Intermediate analysis showed that the stimulatory effect was correlated with removal of oxaloacetate to citrate. Oxaloacetate added alone was shown not to be metabolized until addition of pyruvate and thiamine pyrophosphate; then oxaloacetate was converted in part to pyruvate and citrate. Malate oxidation in mung bean mitochondria apparently is subject to control by oxalocetate levels, which are primarily determined by the results of the activities of malate dehydrogenase, citrate synthase and pyruvate dehydrogenase.