Pyruvate Carboxylase. I. Nature of the Reaction.

The direct carboxylation of pyruvate to oxaloacetate (WoodWerkman reaction) was postulated more than 25 years ago as a probable mechanism for the formation of dicarboxylic acids by CO% fixation (1) and a considerable body of evidence on the interrelationship of dicarboxylic acids and CO2 during bacterial growth was interpreted in this light (24). There was no direct evidence for the existence of such a reaction, however, and as alternative pathways of dicarboxylic acid formation from CO2 were provided by enzymic studies (5-7), the hypothesis of the direct carboxylation of pyruvate assumed less significance. Recently, Woronick and Johnson (8) reported that extracts from Aspergillus niger formed aspartate and malate from pyruvate, COz, and adenosine triphosphate. These authors again suggested that a direct carboxylation of pyruvate to form oxaloacetate might be involved. Our interest in the possibility that such a reaction might occur in animal liver arose from the observations that whereas liver mitochondria can form phosphoenolpyruvate from pyruvate (9--ll), studies of the intracellular distribution of the pertinent enzymes suggested that neither of the previously considered pathways for the formation of phosphoenolpyruvate could be responsible for the observed results with mitochondria. Pyruvate can be converted to phosphoenolpyruvate by a reversal of the pyruvic kinase reaction (12) or by a dicarboxylic acid pathway involving malic enzyme (13, 14) but neither of these enzymes is present in significant amounts in liver mitochondria (15). Since the apparent precursor of phosphoenolpyruvate in liver mitochondria is oxaloacetate we therefore sought a more direct pathway for the formation of this substance from pyruvate. As described in this communication, an enzyme has been detected in and concentrated from liver mitochondria which carries out the following reaction. acetyl-CoA, Mg* Pyruvate + ATP + COZ .