Destroys superoxide anion radicals which are normally produced within the cells and which are toxic to biological systems. 2 H(+) + 2 superoxide = H2O2 + O2 Binds 1 Mn(2+) ion per subunit. Homotetramer. Present in all tissues examined (leaf, petiole, root, latex, callus) with young leaves showing the highest levels in intact plants. Belongs to the iron/manganese superoxide dismutase family.