Pyruvate dehydrogenase and the path of lactate degradation in Desulfovibrio vulgaris Miyazaki F.

Pyruvate dehydrogenase from Desulfovibrio vulgaris Miyazaki F was partially purified from the soluble fraction of the bacterial sonicate, and characterized. The enzyme catalyzes oxidative decarboxylation of pyruvate to produce acetyl-CoA, in contrast to statements in current review articles in which acetyl phosphate is indicated to be a direct decomposition product of pyruvate in sulfate-reducing bacteria. The established reaction stoichiometry is: pyruvate + CoA + FMN----acetyl-CoA + CO2 + FMNH2. The Km values are 2.9 mM for pyruvate, 32 microM for CoA and 6.7 mumol for FMN. Participation of thiamine diphosphate in the enzymic process was not proven. 2-Oxobutyrate, but not 2-oxoglutarate, can substitute for pyruvate. The three flavin compounds, FMN, FAD, and flavodoxin, as well as clostridial ferredoxin, serve as electron carriers for the enzyme. Thus the enzyme is a kind of pyruvate synthase [EC 1.2.7.1], but acts in the direction of pyruvate degradation in the growing cells. The rate of cytochrome C3 reduction is extremely low, but in the presence of flavodoxin as an electron mediator, the reduction rate of cytochrome C3 becomes faster than the reduction rate of flavodoxin alone. It seems that the physiological electron acceptor for this enzyme is flavodoxin, which might be complexed with cytochrome C3 to produce a very efficient electron transfer system in the cell. The soluble fraction of D. vulgaris cells has been proved to contain, in addition to the pyruvate dehydrogenase, lactate dehydrogenase (Ogata, M., Arihara, K., & Yagi, T. (1981) J. Biochem. 89, 1423-1431), phosphate acetyltransferase and acetate kinase, i.e., all the enzymes necessary to convert lactate to acetate, producing ATP by substrate level phosphorylation.