This study identified and characterized three oxygen-metabolizing enzymes in Mycobacterium leprae purified from infected armadillo liver. Superoxide dismutase was detected with low specific activity (less than 1% of other mycobacteria), confirmed as a manganese-containing enzyme through inhibition studies. Peroxidatic activity was demonstrated on polyacrylamide gels as a haemoprotein band, though quantitative assay proved unsuccessful. However, catalase detected in M. leprae extracts appeared to originate from host liver tissue rather than the bacteria themselves, as shown by identical electrophoretic mobility to armadillo liver catalase, resistance to standard inhibitors, and elimination following NaOH treatment of whole bacteria. The authors emphasize the critical importance of distinguishing bacterial from host-derived enzymes in tissue-grown organisms. The deficiency in catalase and low superoxide dismutase activity may contribute to M. leprae's slow growth in vivo and inability to grow in culture media, as these enzymes protect bacteria against toxic oxygen radicals produced by host phagocytes. The work demonstrates methodological rigor necessary for biochemical studies of intracellular pathogens.

Key findings

• Superoxide dismutase identified in M. leprae as a manganese-containing enzyme with low specific activity (less than 1% of other mycobacteria)
• Peroxidatic activity demonstrated in M. leprae as a haemoprotein, detectable only on polyacrylamide gels
• Catalase activity in M. leprae cell-free extracts was confirmed to be host-derived (from armadillo liver) rather than bacterial, as shown by identical electrophoretic mobility and elimination by NaOH treatment
• Low superoxide dismutase activity and absence of true bacterial catalase may explain M. leprae's slow growth in vivo and inability to cultivate in vitro media