FIG. 1.

Mitochondrial ROS generation and defense. Mitochondria are the major producers of ROS, in particular, superoxide anion, as a side effect of electron flow in the respiratory chain, principally from complex I and III. In addition, hydrogen peroxide can be generated by the adaptor protein p66Shc. The antioxidant defense includes a number of enzymatic systems as shown, as well as the GSH redox cycle, to prevent escalating effects through formation of hydroxyl radical that could target proteins, lipids, and DNA.