Amino Acids For Immune Support. Non-GMO. L-cysteine is a conditionally essential amino acid, one of only three sulfur-containing amino acids, the others being taurine (which can be produced from L-cysteine) and L-methionine (from which L-cysteine can be produced in the body by a multi-step process). Cysteine plays a role in the sulfation cycle, acting as a sulfur donor in phase II detoxification and as a methyl donor in the conversion of homocysteine to methionine. Cysteine also helps synthesize glutathione, the bodys most important intracellular antioxidant and a vital detoxifier. Glutathione (L-gamma-glutamyl-L-cysteinyl-glycine) is a peptide molecule synthesized in the body from the three amino acids L-glutamic acid, L-cysteine and glycine. Glutathione is one of the bodys most important and powerful antioxidants, helping to detoxify xenobiotics. A major function of vitamin C is to keep glutathione in its reduced form so that it can continue to provide free radical-quenching effects. Vitamin C, or ascorbic acid, is a white, crystalline, water-soluble substance found in citrus fruits. As an antioxidant, vitamin C scavenges free radicals in the body and protects tissues from oxidative stress. Vitamin C also promotes the absorption of iron, while inhibiting its oxidation. Vitamin C is a vital cofactor to the formation of collagen, the connective tissue that supports arterial walls, skin, bones, and teeth.