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. Nitrated under oxidative stress. Nitration coupled with oxidation inhibits the catalytic activity. Acetylation at Lys-122 decreases enzymatic activity. Deacetylated by SIRT3 upon exposure to ionizing radiations or after long fasting (By similarity). Polyubiquitinated; leading to proteasomal degradation. Deubiquitinated by USP36 which increases protein stability. Belongs to the iron/manganese superoxide dismutase family.