[(Science: biochemistry) The tripeptide _ glutamylcysteinylglycine. It contains an unusual peptide Linkage between the _ carboxyl group of the glutamate side chain and the amine group of cysteine. The concentration of glutathione in animal cells is _5mM and its sulphydryl group is kept largely in the reduced state. this allows it to act as a sulphydryl buffer, reducing any disulphide bonds formed within cytoplasmic proteins to cysteines. Hence, few, if any, cytoplasmic proteins contain disulphide bonds. glutathione is also important as a cofactor for the enzyme glutathione peroxidase, in the uptake of amino acids and participates in leucotriene synthesis.