The Oxidation of Malate by Mitochondria Isolated from Cauliflower Buds

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Abstract
Pyruvate is the major product of malate oxidation by isolated cauliflower bud mitochondria when pyruvate dehydrogenase is inhibited. Pyruvate formation, which requires Mg++, Mn++ or Co++, is stimulated by added NAD. The effects of ADP, 2,4‐dinitrophenol and respiratory inhibitors on pyruvate formation indicate that the reaction is linked to mitochondrial electron transport. No enzymic decarboxylation of oxaloacetate to pyruvate by the mitochondria can be observed. With added malate oxaloacetate breaks down in the mitochondria, probably to malate using NADH generated by a mitochondrial malic enzyme. Acetyl‐CoA and glutamate, which compete for oxaloacetate in the mitochondria, do not inhibit pyruvate formation from malate. A solubilised NAD requiring malic enzyme is present in sonicates of the mitochondria. It is concluded that oxaloacetate is not an intermediate in pyruvate formation during malate oxidation by cauliflower bud mitochondria, and that a direct conversion of malate to pyruvate by a mitochondrial NAD requiring malic enzyme occurs.