GSH is a tripeptide (γ-glutamylcysteinylglycine) widely distributed in both plants and animals. GSH serves as a nucleophilic co-substrate to glutathione transferases in the detoxification of xenobiotics and is an essential electron donor to glutathione peroxidases in the reduction of hydroperoxides. GSH is also involved in amino acid transport and maintenance of protein sulfhydryl reduction status. The concentration of GSH ranges from a few micromolar in plasma to several millimolar in tissues such as liver.