GSH is a tripeptide (γ-glutamylcysteinylglycine) widely distributed in both plants and animals.{1813,4672} 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.{4672,165} GSH is also involved in amino acid transport and maintenance of protein sulfhydryl reduction status.{4669,4670} The concentration of GSH ranges from a few micromolar in plasma to several millimolar in tissues such as liver.