1) A tripeptide with many roles in cells. It conjugates to drugs to make them more soluble for excretion, is a cofactor for some enzymes, is involved in protein disulfide bond rearrangement and reduces peroxides.

2) Tripeptide composed of gamma-glutamate, cysteine, and glycine; an important endogenous reducing agent involved in oxidative respiration and free radical scavenging.

3) The peptide gamma-glutamylcysteinylglycine.

4) A tripeptide present in most cells comprised of three amino acids (cysteine, glutamic acid, and glycine) acting as an antioxidant, enhancing free radical scavenging, a detoxifying agent, binding to and transforming chemicals into excretable forms, a co-factor for some enzymes, and to boost the immune system.(NCI)