Superoxide Dismutase and Oxygen Metabolism in Streptococcus faecalis and Comparisons with Other Organisms

Abstract

Streptococcus faecalis contains a single superoxide dismutase that has been purified to homogeneity with a 55% yield. This enzyme has a molecular weight of 45,000 and is composed of two subunits of equal size. It contains 1.3 atoms of manganese per molecule. Its amino acid composition was determined and is compared with that for the superoxide dismutases from Escherichia coli, Streptococcus 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 oxygen consumption by such extracts, in the presence of reduced nicotinamide adenine dinucleotide, was associated with the production of O 2 − . A variety of bacterial species were surveyed for their content of superoxide dismutases. The iron-containing enzyme was distinguished from the manganese-containing enzyme through the use of H 2 O 2 , which inactivates the former more readily than the latter. Some of the bacteria appeared to contain only the iron enzyme, others only the manganese 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.