superoxide

 O2 is converted to superoxide (O2-) by oxidative enzymes in the endoplasmic reticulum (ER), mitochondria, plasma membrane, peroxisomes, and cytosol.

 O2- is converted to H2O2 by dismutation and thence to OH by the Cu2+/Fe2+-catalyzed Fenton reaction. H2O2 is also derived directly from oxidases in peroxisomes.

Resultant free radical damage to lipid (peroxidation), proteins, and DNA leads to various forms of cell injury.

02- superoxide catalyzes the reduction of Fe3+ to Fe2+, thus enhancing OH generation by the Fenton reaction. The major antioxidant enzymes are superoxide dismutase (SOD1), catalase, and glutathione peroxidase.

See also

 ocydative stress
 reactive oxygen species (ROS)

References

 Salvemini D, Cuzzocrea S: Superoxide, superoxide dismutase and ischemic injury. Curr Opin Investig Drugs 3:886, 2002.