Destroys superoxide anion radicals which are normally produced within the cells and which are toxic to biological systems (By similarity). Plays important role in chloroplast development, particularly in the maintenance of thylakoids membranes. Seems to act as a heterodimer with FSD2. 2 H(+) + 2 superoxide = H2O2 + O2 Binds 1 Fe cation per subunit. Activated by cpn20/cpn21 (in vitro). Homodimer. Heterodimer with FSD2 (PubMed:18996978). Interacts with MRL7 (PubMed:23956074). Pale green phenotype. Abnormal plastids, highly vacuolated and without internal membrane structures like thylakoids. Belongs to the iron/manganese superoxide dismutase family.