Dismutation or disproportionation is a type of redox reaction in which a substrate is simultaneously reduced and oxidized to form two different products. As such, the free radical species superoxide is converted into hydrogen peroxide and oxygen by the enzyme Superoxide Dismutase (SOD; EC 126.96.36.199), enzymes responsible for the homeostasis of low levels of reactive oxygen species (ROS). Three forms of superoxide dismutase (SOD1-3) are known to date in mammals, of which SOD1 is located primarily in the cytoplasm, SOD2 in the mitochondria and SOD3 is extracellular. SOD1 and SOD3 are copper/zinc-dependent enzymes, while SOD2 functions by incorporation of manganese in the active site. The harmful species hydrogen peroxide formed by the SOD enzymes can be converted into water (and oxygen) in turn by the enzymes catalase (EC 188.8.131.52) and multiple peroxiredoxins (EC 184.108.40.206), and glutathione. Point mutations of SOD1 are reported to be related to the familial form of amyotrophic lateral sclerosis (ALS), a neurological disease that causes the death of motor neurons with consequent muscular paralysis.
 I.N. Zelko, T.J. Mariani, R.J. Folz. Superoxide dismutase multigene family: a comparison of the CuZn-SOD (SOD1), Mn-SOD (SOD2), and EC-SOD (SOD3) gene structures, evolution, and expression. Fr. Rad. Biol. Med. 2002, 33, 337-349.
 L. Banci et al. SOD1 and amyotrophic lateral sclerosis: mutations and oligomerization. PLoS One. 2008, 3, e1677.