Aspartate metabolism in Mycobacterium avium grown in host tissue and axenically and in Mycobacterium leprae

Aspartokinase activity was detected in extracts from Mycobacterium leprae (recovered from armadillo liver) and in Mycobacterium avium grown axenically and in vivo. Homoserine dehydrogenase activity was only detected in M. leprae and in M. avium grown axenically. Activities, when detected, were 50 to 70% lower in M. leprae or M. avium grown in vivo than in axenically grown M. avium. In these two pathogenic mycobacteria, aspartokinase and homoserine dehydrogenase are subject to feedback inhibition by methionine - an additional regulator over those observed for the enzymes from Mycobacterium smegmatis. Intact mycobacterium incorporated carbon from [U-14C]aspartate into the aspartate family of amino acids (threonine, isoleucine, methionine and lysine) though the rate of incorporation in M. avium grown in vivo was about half that in M. avium grown axenically.