Fig. 2. Generation of ROS. The superoxide (O2-) is generated from O2as a by-product of respiratory chain complex in the mitochondria or by NADPH oxidase. By superoxide dismutase (SOD), the superoxide (O2-) can be transformed into hydrogen peroxide (H2O2), which can be further transformed to a number of other ROS such as hydroxyl radicals (·OH) and hydroxyl anions (OH-).
