Destroys superoxide anion radicals which are normally produced within the cells and which are toxic to biological systems. Catalyzes the dismutation of superoxide anion radicals into O2 and H2O2 by successive reduction and oxidation of the transition metal ion at the active site. 2 H(+) + 2 superoxide = H2O2 + O2 Binds 1 Mn(2+) or Fe(3+) ion per subunit. Belongs to the iron/manganese superoxide dismutase family.