Superoxide Dismutase and Oxygen Metabolism inStreptococcus faecalisand Comparisons with Other Organisms

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Abstract
S. faecalis contains a single superoxide dismutase that was purified to homogeneity with a 55% yield. This enzyme has a MW of 45,000 and is composed of 2 subunits of equal size. It contains 1.3 atoms of Mn/molecule. Its amino acid composition was determined and is compared with that for the superoxide dismutases from Escherichia coli, S. mutans and Mycobacterium lepraemurium. When used as an antigen in rabbits, the S. faecalis enzyme elicited the formation of a precipitating and inhibiting antibody. This antibody cross-reacted with the superoxide dismutase present in another strain of S. faecalis, but neither inhibited nor precipitated the superoxide dismutases in a wide range of other bacteria, including several other streptococci, such as S. pyogenes, S. pneumoniae and S. lactis. The inhibiting antibody was used to suppress the superoxide dismutase activity present in cell extracts of S. faecalis and thus allow the demonstration that 17% of the total O2 consumption by such extracts, in the presence of NADH, was associated with the production of O2-. A variety of bacterial species were surveyed for their content of superoxide dismutases. The Fe-containing enzyme was distinguished from the Mu-containing enzyme through the use of H2O2, which inactivates the former more readily than the latter. Some of the bacteria appeared to contain only the Fe enzyme, others only the Mn enzyme, and still others both. Indeed, some had multiple, electrophoretically distinct superoxide dismutases in both categories. There was no discernible absolute relationship between the types of superoxide dismutases in a particular organism and their gram-stain reaction.