Figure 2.

Reactive oxygen species production and toxicity. Oxygen accepts an electron to form superoxide (O₂^•−). O₂^•− can react with NO^• to form peroxynitrite (ONOO⁻) or be converted to H₂O₂ by superoxide dismutase (SOD). H₂O₂ can serve as signaling molecule and be converted to H₂O by glutathione peroxidase (GPx) and catalase (CAT). H₂O₂ can also react with transition metals, such as Fe²⁺, through the Fenton reaction to form hydroxyl radical (HO^•), which if not adequately detoxified, can result in oxidative damage to proteins, DNA and lipids.