Glutathione is a cysteine-containing peptide (amino acid, see proteins) found in most aerobic life-forms. Human cells manufacture substantial amounts gluthathione, depending on the stresses imposed on the body, and therefore, is not required in the normal diet. Our cells produce glutathione from the use of other amino acids. However, if we choose to use glutathione for its' antioxidant properties, we must suppliment our diet with it (eg., through tablet form). The antioxidant properties of glutathione come from its thiol group in its cysteine component. The thiol group (molecule) can be reversibly oxidized and reduced, and therefore, protect cells from oxidation. In cells, Glutathione is engineered to remain in the active form by our cellular enzyme, known as glutathione reductase. Glutathione has a central antioxidant role in many cellular s systems of the human and is one of the most important of the antioxidants.