DEGRADATION OF PYRUVATE BY MICROCOCCUS LACTILYTICUS I

Abstract

McCormick, N. G. (University of Washington, Seattle), E. J. Ordal, and H. R. Whiteley. Degradation of pyruvate by Micrococcus lactilyticus. I. General properties of the formate-exchange reaction (J. Bacteriol. 83:887–898. 1962.—At an alkaline pH, extracts of Micrococcus lactilyticus² catalyze the phosphoroclastic degradation of pyruvate to formate and acetyl phosphate and the rapid exchange of formate into the carboxyl group of pyruvate. At an acid pH, hydrogen, carbon dioxide, and acetyl phosphate are produced, and carbon dioxide is exchanged into the carboxyl group of pyruvate. A concentration of approximately 1 m phosphate is required for the phosphoroclastic reaction and formate exchange; the production of carbon dioxide and hydrogen is greatly inhibited by high concentrations of phosphate. Formate exchange requires a divalent metal ion and is stimulated by reducing agents and an atmosphere of hydrogen. Inhibition by p-chloromercuribenzoate, Zn⁺⁺, Cd⁺⁺, and arsenite indicates that sulfhydryl groups on the enzyme are involved in the reaction; the inhibition by arsenite and Cd⁺⁺ may be relieved by 2,3-dimercaptopropanol, suggesting that vicinal dithiols may be required. Inhibition by hypophosphite may reflect a competition with formate for a site on the enzyme. At an alkaline pH, α-ketobutyrate is degraded to propionate and formate, whereas α-ketoglutarate is fermented to succinate, propionate, carbon dioxide, hydrogen, and formate. Formate is exchanged into the carboxyl groups of α-ketobutyrate and α-ketoglutarate under these conditions. Only traces of α-ketovalerate and α-ketoisovalerate are fermented at an alkaline pH and the exchange of formate into these compounds is very low. The addition of viologen dyes under the conditions used for formate exchange causes a reduction of pyruvate, α-ketobutyrate, α-ketovalerate, and α-ketoisovalerate to the corresponding α-hydroxy acids.