No abstract

and properties of enzymes involved in the propionic acid fermentation. J. Bacteriol. 87:171-187. 1964.-Chromatographic procedures are described for the separation and purification of phosphotransacetylase, acetyl kinase, malic dehydrogenase and coenzyme A (CoA) transferase. Purity of the enzymes was judged by homogeneity in an ultracentrifuge and by specific activity. Phosphotransacetylase was obtained 85% pure with a specific activity of 27.1. The preparation of acetyl kinase was a homogeneous protein with a specific activity of 531. The malic dehydrogenase likewise was homogeneous with a specific activity of 938. The CoA transferase, which was about 56% pure with a specific activity of 42.6, is the purest preparation of this enzyme yet described. The pH optimum was 6.5 to 7.8, and the Km for succinyl-CoA in the transfer of CoA to acetate was found to be 1.3 X 10-4 M; for acetate, in the same transfer, the Km was 7.0 X 10-3 M; for succinyl-CoA to propionate it was 6.8 X 10-5M, and for propionate, in the same reaction, 6.2 X 104 M. Methods are described for the enzymatic production of methylmalonyl-CoA, malonyl-CoA, propionyl-CoA, acetyl-CoA, and succinyl-CoA. The role of these enzymes in the propionic acid fermentation as well as the possible mechanism responsible for the high yields of adenosine triphosphate from glucose are considered. The formation of propionate by propionibacteria has been extensively investigated, and the pathway is known to involve a number of enzymes which have been purified and studied. These include methylmalonyl-oxaloacetic trans

When glucose was present in high concentration, Candida albicans formed filaments in a phosphate-buffered medium, regardless of the nitrogen source. In lower concentrations of glucose, filamentation occurred only when various members of the glutamate, succinyl, or acetoacetyl-coenzyme A families of amino acids were used as sole nitrogen sources. Yeast morphology could be maintained either by replacing the amino acids in the medium with ammonium chloride or by making the medium high in phosphate or biotin. Studies using [U-14C]proline indicated that proline was catabolized in a manner consistent with the generation of increased cellular reducing potential and that the proline label entered into the Kreb's cycle. A reduction in Kreb's cycle activity was evidenced by an initial increase and then a rapid drop of the total organic acid content of the cells as well as in specific Kreb's cycle intermediates. Filamentation under conditions of low phosphate, high glucose, and increased cellular reduction potential, accompanied by a decrease in Kreb's cycle activity, suggests that morphogenesis in C. albicans is correlated with a Crabtree-like effect, i.e., repression of mitochondrial activity.

Glucose metabolism and respiration of Candida albicans were compared under conditions which permitted either maximal filamentous or maximal yeast growth. Changes in metabolism were monitored by comparing the quantities of ethanol produced, CO2 evolved, and oxygen consumed. Filamenting cultures produced more ethanol and less CO2 than yeasts, with oxygen consumption in the former concomitantly slower than that of the latter. Studies involving cofactors and inhibitors associated with electron transport imply that a transfer of electrons away from flavoprotein is required for maintenance of yeast morphology. Conditions consistent with a buildup of reduced flavoprotein, however, favored filament formation. These changes were expressed metabolically as a shift from an aerobic to a fermentative metabolism. The results presented are consistent with hypotheses correlating filament production with changes in carbohydrate metabolism and an interruption of electron transfer within the cell.