**7.3 Superoxide oxygen (O2∙—one electron)**

It is generated by direct auto-oxidation of O2 during mitochondrial electron transport reaction. Alternatively, O2∙ is produced enzymatically by xanthine oxidase and cytochrome P450 in the mitochondria or cytosol [121]. O2∙ so formed is catabolized to produce H2O2 by superoxide dismutase (SOD), a metalloprotein. It is considered to be the least reactive type of ROS and the most commonly produced free radical in humans. Once it is produced, it triggers a rapid cascade of events that creates other free radicals.
