Fig. 1
Generation of reactive oxygen species (ROS) from mitochondria. O2·− is formed from molecular O2 by the gain of a single electron from electron leakage in the electron transport chain (ETC) of mitochondria. Superoxide dismutase (SOD) enzymes convert two superoxide molecules into hydrogen peroxide (H2O2) and a water (H2O) molecule. Moreover, hydrogen peroxide is converted to the highly reactive ROS, the hydroxyl radical (OH.-), in the presence of iron (Fe2+), which further causes damage to the cell structure including proteins, lipids, membranes, and DNA. Alternatively, hydrogen peroxide can be reduced to water by glutathione (GSH) peroxidase (GPx) or catalase