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 Fe cation per subunit. Homotetramer. Belongs to the iron/manganese superoxide dismutase family. Although found extracellularly, no signal sequence is present. An alternative secretory pathway may be used.