The biological chemistry of hydrogen peroxide.

Hydrogen peroxide is generated in numerous biological processes and is implicated as the main transmitter of redox signals. Although a strong oxidant, high activation energy barriers make it unreactive with most biological molecules. It reacts directly with thiols, but for low-molecular-weight thiols and cysteine residues in most proteins, the reaction is slow. The most favored reactions of hydrogen peroxide are with transition metal centers, selenoproteins, and selected thiol proteins. These include proteins such as catalase, glutathione peroxidases, and peroxiredoxins, which, as well as providing antioxidant defense, are increasingly being considered as targets for signal transmission. This overview describes the main biological reactions of hydrogen peroxide and takes a kinetic approach to identifying likely targets in the cell. It also considers diffusion of hydrogen peroxide and constraints to its acting at localized sites.