Metabolic inhibitors of host-tissue origin in Mycobacterium leprae

It is not clear why host-derived bacteria are metabolically inert, compared to organisms grown in vitro. o-Diphenoloxidase is the only metabolic property proven to be present in Mycobacterium leprae separated from infected human as well as animal (mouse and armadillo) tissues. However, highly concentrated suspensions of M. leprae obtained from the organs of experimentally infected armadillos showed little or extremely low o-diphenoloxidase, while the organisms bound 14C-labeled dopa. When these preparations were diluted, they readily oxidized D-dopa to pigment. The activity remained unaltered by washing the suspensions with dilute alkali or acetone and ether, indicating that it is an intrinsic property of the bacilli. Treatment with different proteases relieved the inhibition, and resulted in a 100% stimulation of O-diphenoloxidase in the bacilli. Evidently, the M. leprae suspensions obtained from infected tissues contain an inhibitory material which is protein in nature, and the metabolic inertness sometimes observed in host-grown bacteria may not be due to loss of enzymes or metabolites from the organisms.