02

ROS reactive oxygen species

 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 (SOD), catalase, and glutathione peroxidase.