Superoxide dismutase activity of Mycobacterium avium complex (MAC) strains isolated from AIDS patients

Abstract

Objective: To explore whether Mycobacterium avium complex (MAC) strains isolated from AIDS patients produce and secrete superoxide dismutase (SOD). Design: SOD was assayed in the crude extracts and in cell-free medium of 18 MAC strains (MAC 101, LR and SK strains) isolated from AIDS patients to determine intracellular and extracellular activity. The SODs were characterized by PAGE and by their sensitivity to azide, cyanide and hydrogen peroxide. Results: SOD activity was detected in cell extracts as well as in extracellular medium of all AIDS-MAC strains. PAGE demonstrated a single activity band for each strain, though there were differences in mobility. All LR strains demonstrated an activity band with R f = 0.30, while SOD band for MAC 101 and for SK strains migrated further (R f = 0.87). The differences in mobility correlated with differences in sensitivity to NaN 3 and H 2O 2. The SOD activity of LR strains was irreversibly inhibited 100% by 5 mM H 2O 2, and exhibited greater sensitivity to NaN 3, suggesting the presence of iron in the enzyme. The SOD activity of SK strains and MAC 101, however, was not inhibited by 5 mM H 2O 2 but was inhibited to a lesser extent by NaN 3, which is characteristic of a manganese-containing SOD. Conclusion: Our data indicate that MAC strains are rich in manganese- or iron-containing SOD, which could contribute to the organism's resistance to the oxidative burst of activated macrophages. The secretion of SOD may play an important role in the pathogenesis of MAC strains.