Citrulline can be made in the body from ornithine by the addition of carbon dioxide and ammonia, and can also be converted in the body to arginine. Citrulline promotes the detoxification of ammonia (nitrogen) in the blood and is sometimes helpful in problems of fatigue. It is also thought to stimulate the immune defense system.
GABA is gamma-aminobutyric acid, an inhibitory neurotransmitter formed from glutamine. It is discussed under Glutamic Acid.
Glutathione (GTH) is actually a tripeptide composed of three amino acids—cysteine, glutamic acid, and glycine. Cysteine is the important amino acid here; it controls the amount of glutathione made in the liver and gives GTH its metabolic power as an antioxidant and detoxifier. Since GTH is not easily available or usable by its oral administration (it breaks down into the individual amino acids), L-cysteine is usually supplemented to enhance glutathione production by the liver. Since methionine can be converted to cysteine, it may also be helpful.