Oxaloacetic decarboxylase from rat liver mitochondria.

In a previous communication (l), an accumulation of oxaloacetic acid was implicated as the cause of a decline of succinate oxidation in liver mitochondria from rats fed a diet deficient in vitamin E. This conclusion appeared justified from observations that compounds known to accelerate the removal of oxalo.acetate would relieve this decline of succinate oxidation. There was, however, a lack of effect of inosine triphosphate on the decline. Several workers have shown the stimulatory effect of inosine triphosphate on oxaloacetic acid decarboxylases isolated from chicken and lamb liver, in the process that involves the formation of phosphoryl-enolpyruvate from oxaloacteate (2, 3). The lack of relief of the decline of succinate oxidation by inosine triphosphate suggested that the oxaloacetic decarboxylase activity at pH 7.5 which occurs in rat liver mitochondria might be due to a nucleotide-independent enzyme. It did not seem likely that the nucleotide-independent oxaloacetic acid decarboxylase activity of the malic enzyme was involved, because this enzyme is not active at pH 7.5 (4). Upon fractionation of rat liver mitochondria, an enzyme was partially purified which catalyzes the formation of carbon dioxide and pyruvate from oxaloacetic acid, and which is nucleotide-independent. This enzyme appears to account for most of the oxaloacetic decarboxylase activity of the mitochondria, since little nucleotidedependent activity was found.