Fig. 6.

The major sources of Reactive Oxygen Species. (A) There are many antioxidant defense mechanisms, including enzymatic and nonenzymatic. (B) A byproduct of the mitochondrial ETC is superoxide (O₂•^-). Under normal conditions, MnSOD converts O₂•^- to hydrogen peroxide (H₂O₂) (C) There are many endogenous sources of ROS, including xanthine oxidase, nitric oxidase, ETC, peroxisomes, and NADPH oxidase.

Abbreviations: ETC: electron transport chain, ROS: Reactive oxygen species, SOD: superoxide dismutase, GPx: glutathione peroxidase, ATP: adenosine triphosphate, NADH: nicotinamide adenine dinucleotide, ER: endoplasmic reticulum.