Superoxide dismutase and catalase activities in purified Frankia vesicles

Superoxide dismutase (EC 1.15.1.1.) and catalase (EC 1.11.1.6.) activities of Frankia cells grown in the presence of ammonium were very high in comparison with those of other prokaryaotes and particularly Rhizobium . Furthermore, these activities were significantly enhanced under nitrogen-fixing conditions where vesicles were produced. By using a single-step sucrose gradient, Frankia vesicles were isolated and appeared intact and free of hyphal contamination. The contents of superoxide dismutase and catalase in the purified vesicles were similar to those in preparations containing both vesicles and hyphae. These results suggest an important role of superoxide dismutase and catalase in the protection of the overall nitrogen-fixation process against O₂ in Frankia vesicles. Beside the protective role played by the thick walls of the vesicles, the presence of specialized enzymes is emphasized.