The mechanism of the pyruvate, phosphate dikinase reaction.

and Summary.-Pyruvate, phosphate dikinase has been purified from propionic acid bacteria and evidence is presented in this report to show that the over-all reaction involves the following reactions: Enzyme + ATP ; enzyme-PP + AMP (1) Enzyme-PP + Pi T± enzyme-P + PPi (2) Enzyme-P + pyruvate T± enzyme + P-enolpyruvate (3) Mg2 + Sum: Pyruvate + ATP + Pi P-enolpyruvate + AMP + PPj. (4) The enzyme combines with ATP to form an enzyme-diphosphate compound and AMP, with the ,f and y phosphates from ATP bound to the enzyme (reaction 1). The a-phosphate of the enzyme-diphosphate then combines with orthophosphate to give pyrophosphate and enzyme-phosphate (reaction 2). The ,8-phosphate is then transferred from the enzyme-P to pyruvate to produce free enzyme and P-enolpyruvate (reaction 3). The sum of the three reactions is reaction 4, which is the over-all reaction catalyzed by pyruvate, phosphate dikinase. The propionic acid bacteria grow well on lactate and pyruvate and therefore must be able to convert pyruvate to P-enolpyruvate, which is required for the netformation of 4-carbon compounds, carbohydrates, glycerol, and other cell materials. Investigation (unpublished) has revealed that the conversion of pyruvate to P-enolpyruvate does not occur via oxalacetate, nor by a reversal of the pyruvate kinase reaction. We have found1 that the conversion resembles that catalyzed by P-enolpyruvate synthase, which was discovered in E. coli by Cooper. and Kornberg2 and which catalyzes the following reaction: