Role of various carbon and nitrogen sources in the regulation of enzymes of pyrimidine biosynthesis in Mycobacterium smegmatis TMC 1546.

Pyrimidine biosynthesis and its regulation in the presence of different carbon and nitrogen sources in the growth medium of Mycobacterium smegmatis were studied. M. smegmatis TMC 1546 cells grown in shake culture were found to have marginally higher pyrimidine enzyme biosynthesis activities than cells grown in static culture. The activity was highest at the mid-log phase of growth during both surface and shake cultures, suggesting that the cells were metabolically most active at this stage of growth. Replacement of glycerol by glucose and fructose slightly increased the activities of carbamyl phosphate synthetase and aspartate transcarbamylase. The enzyme activities involved in pyrimidine biosynthesis decreased when citrate was replaced by succinate, fumarate, pyruvate or acetate in the growth medium. The activities of the enzymes in pyrimidine biosynthesis were found to decrease when asparagine as a nitrogen source in the medium was replaced by glutamate, glutamine or ammonium chloride. The presence of ornithine in place of asparagine in the growth medium increased these enzyme activities, while the presence of arginine instead of asparagine in the growth medium decreased these enzyme activities, though the differences in activity were small. The activity of aspartate transcarbamylase in vitro was inhibited by arginine. In the case of cells grown in the presence of ornithine, the activity of aspartate transcarbamylase was induced by ornithine, but inhibited by arginine.