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. Activated by cpn20/cpn21. Homodimer. Interacts with cpn20/cpn21. A number of isoforms are produced. According to EST sequences. Circadian-regulation. Down-regulated upon photosynthetically active radiation (PAR) (e.g. light fluence) increase and in response to ozone fumigation. Belongs to the iron/manganese superoxide dismutase family. Extended N-terminus.