glutathione, a tripeptide (i.e., compound composed of three amino acids), the chemical name of which is γ-l-glutamyl-l-cysteinylglycine. Widely distributed in nature, it has been isolated from yeast, muscle, and liver. Glutathione has a role in the respiration of both mammalian and plant tissues and protects red blood cells against hydrogen peroxide, which is a toxic by-product of many metabolic reactions, by reducing the peroxide to water. It serves as a cofactor for various enzymes; e.g., glyceraldehyde-3-phosphate dehydrogenase, to which it becomes firmly bound.