DEGRADATION OF PYRUVATE BY MICROCOCCUS LACTILYTICUS I

Abstract

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, ZnH, 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, oa-ketobutyrate is degraded to propionate and formate, whereas a-ketoglutarate is fermented to succinate, propionate, carbon dioxide, hydrogen, and formate. Formate is exchanged into the carboxyl groups of aketobutyrate and a-ketoglutarate under these conditions. Only traces of a-ketovalerate and

Pyruvate metabolism by aminopterin-inhibited Aerobacter aerogenes

“…The possibility that a folinic acid derivative forms the primary acceptor of the C1 unit has been suggested by Chin et al (1957) and Wood & O'Kane (1964), although Oster & Wood (1964) consider that any stimulation of exchange activity by tetrahydrofolic acid is due to the maintenance of the necessary oxidation-reduction potential, and is unrelated to coenzyme function. Also, in A. aerogenes, as in M. tactilyticu8 (McCormick et al 1962b), tetrahydrofolic acid does not stimulate formate exchange. Although this could indicate a requirement for a different form of the coenzyme, as has been found for other folinic acid-dependent reactions in A. aerogenes (Jones, Guest & Woods, 1961;Morningstar & Kisliuk, 1965), the direct inhibition by aminopterin of the exchange and phosphoroclastic activities of this organism cannot be explained by 'folic acid antagonism'.…”

“…where TPP represents thiamine pyrophosphate. The authors consider that in such a scheme the unidentified labile cofactors that are necessary for formate exchange (Strecker, 1951;Novelli, Gest & Krampitz, 1954;Asnis, Fritz & Glick, 1956;Wood & O'Kane, 1964;McCormick et al 1962b) may be required for the interconversion of 'Ci' and formate.…”

“…It is therefore probable that the sensitivity of these enzyme systems to aminopterin is due to the inactivation or displacement of an unidentified cofactor that is necessary for both exchange and phosphoroclastic activities (e.g. Wood & O' Kane, 1964;McCormick et al 1962b) and that is present in heat-treated extracts of normal cells.…”