Pyrimidine biosynthesis in Mycobacterium leprae and other intracellular mycobacteria

All the enzymes which could be detected in mycobacteria that are unique to the de novo pathway of pyrimidine biosynthesis were shown (in cell extracts) in M. leprae. Activity of the first enzyme in the pathway, aspartate transcarbamylase was shown in M. microti and M. avium grown in vivo and in liquid Dubos medium. This suggested that the very low activity of pyrimidine biosynthesis de novo in intact M. microti and M. avium grown in vivo, and the failure to detect any activity in M. leprae, is a result of feedback inhibition of the metabolic pathway for pyrimidine biosynthesis as opposed to any lack of metabolic capability.