Superoxide and the Superoxide Dismutases: An Introduction by Irwin Fridovich

The univalent reduction of molecular oxygen to superoxide is the facile pathway for oxygen reduction because of the spin restriction facing its divalent reduction by pairs of spin-opposed electrons. The reactivity of superoxide, and of its conjugate acid the hydroperoxyl radical, threatens aerobic life. Defenses are essential and these are provided by superoxide dismutases (SODs) that efficiently catalyze the conversion of superoxide into oxygen plus hydrogen peroxide. Several SODs are known. These include the Cu,ZnSODs, MnSODs, FeSODs, and NiSODS. An adequate defense against the toxicity of oxygen must also include enzymes that scavenge H2O2, such as the catalases and peroxidases, as well as enzymes that allow repair of that damage that does occur despite the protective actions of the defensive enzymes.