Fig. 3
From: Role of reactive oxygen species in ultraviolet-induced photodamage of the skin
Production and regulation of reactive oxygen species (ROS). Mitochondria and NADPH oxidases (NOXs) are the two main contributors of endogenous ROS. O2• − is formed from molecular O2 following the acceptance of a single electron from the electron transport chain (ETC) in the mitochondria or from NOXs. Superoxide dismutase (SOD) enzymes convert O2 •− into H2O2, which can then be reduced and converted by peroxiredoxin (PRX), glutathione peroxidase (GPX), and catalase to form H2O and OH•. The latter is extremely reactive and causes damage to DNA, proteins, and lipids