A biological molecule that is a tripeptide comprising the three amino acids glutamate, cysteine, and glycine, and is involved in multiple metabolic processes. While the cysteine residue is linked to the glycine residue through a normal α-amide bond, the glutamate residue is linked to the cysteine residue through an unusual γ-amide bond. Glutathione is found in reduced and oxidized forms (Fig. 1). The reduced form (GSH) contains only a single glutathione unit with the side chain of cysteine in the sulfhydryl form. The oxidized form (glutathione disulfide, GSSG) contains two glutathione units covalently attached through a disulfide bridge between the cysteine residues.