Figure 1.
Origin and pleiotropic effects of reactive oxygen (ROS) and nitrogen species (RNS). Superoxide anion () is generated by the mitochondrial respiratory chain and by NOXs.
is then converted to hydrogen peroxide (H2O2) by the superoxide dismutase enzyme. H2O2 can further react with Fe2+ to produce hydroxyl radical (HO•) by the Fenton reaction. Nitric oxide (•NO) is synthesized from l-arginine by the action of NOSs. Nitric oxide can react with
to produce peroxynitrite (OONO−). ROS (H2O2, HO•,
) and RNS (•NO, OONO−) modulate various cellular processes. (Online version in colour.)