The role of redox in the regulation of manganese-containing superoxide dismutase biosynthesis in Escherichia coli

The manganese-containing superoxide dismutase in Escherichia coli is an inducible enzyme that protects cells against oxygen toxicity. The manganese-enzyme is induced by oxygen, nitrate, redox active compounds that react with oxygen to generate superoxide radicals, as well as iron chelators. In order to test the hypothesis that the redox state of the cell is involved in regulating manganese-superoxide dismutase biosynthesis, we studied the effects of several oxidants on growth and superoxide dismutase biosynthesis. The data showed, that under anaerobic conditions, the active manganese-enzyme is induced in the presence of potassium ferricyanide, copper-cyanide complex, ammonium persulfate, and hydrogen peroxide. Western blot analysis revealed that the induction of manganese-superoxide dismutase by the oxidants is associated with de novo protein biosynthesis. Potassium ferricyanide and hydrogen peroxide induced the enzyme under aerobic conditions as well. It is concluded that the redox state of the cell possibly influences the biosynthesis and/or activity of an iron-containing repressor protein that serves to negatively regulate manganese-superoxide dismutase biosynthesis.