Enzymatic Synthesis of Citrate from Pyruvate and Oxalacetate

Abstract

SOLUBLE enzyme preparations from Escherichia coli and Streptococcus fæcalis catalyse the dismutation of two molecules of pyruvate to acetyl phosphate, lactate and carbon dioxide when orthophosphate is present. Acetyl phosphate was determined by Lipmann's hydroxylamine reaction¹. The system is almost inactive in the absence of added diphosphopyridine nucleotide (DPN). Maximum reaction-rates require, in addition to enzyme, substrate and pyridine nucleotide, the following components: orthophosphate, magnesium ions (Mg⁺⁺) or manganese ions (Mn⁺⁺), diphosphothiamine, a boiled extract of yeast, and lactic dehydrogenase. Coenzyme A is required for maximum yields of acetyl phosphate. The nature of the active factor in yeast extract is unknown; but it is not coenzyme A. It is possible that the compound may be a coenzyme form of the factor of O'Kane and Gunsalus² required for oxidative decarboxylation of pyruvate by S. fæcalis cells. In the absence of orthophosphate, the reaction-rate is sharply reduced and no acetyl phosphate accumulates. The dismutation can be formulated as follows: