Superoxide dismutase and catalase in Frankia

Abstract

Superoxide dismutase (SOD) and catalase (CAT) are important enzymes in the protection of cell components from oxidation via superoxide free radicals [Formula: see text] and hydrogen peroxide (H2O2). SOD and CAT activities in Frankia, under non-nitrogen fixing conditions, are among the highest reported in prokaryotes. A sixfold increase in SOD activity (2150 units/mg of protein) and a twofold increase in CAT activity (413 units/mg of protein) was seen in cultures derepressed for nitrogen fixation compared with ammonium-grown cultures. Frankia possesses a manganese-containing SOD (MnSOD) when grown with ammonium as the nitrogen source. An additional SOD isozyme containing iron (FeSOD) was detected in cell extracts when grown with dinitrogen. Methyl viologen induced higher activity of the MnSOD in ammonium-grown cultures but failed to induce the FeSOD. During derepression of nitrogenase activity, the simultaneous induction of SOD and CAT was detected. The presence of a new iron-containing SOD under nitrogen-fixing conditions could provide an additional mechanism for protection from O2 toxicity.