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Cysteine

Cysteine is a non-essential amino acid necessary for the formation of sulfur containing compounds such as pyruvate, taurine, and glutathione, important in normal tissue metabolism protection and repair. Cysteine is a sulfur containing amino acid, which includes three forms--the optically active D-form, the optically active L-form and the optically inactive DL-form (racemate) which is an equivalent weight mixture of the D-form and the L-form. At present, L-cysteine is a predominant product, because it is industrially produced by extraction from hydrolyzates of natural materials, and it has been used for producing medicines, food additives, cosmetics and feed stuffs, etc. L-cysteine is a quasi-essential amino acid which is useful as a food additive and a pharmaceutical, e.g., as an antidote. In addition, L-cysteine is useful as an intermediate in the preparation of other pharmaceutical compounds. The derivatives of L-cysteine, for example, the sulfoxides of S-methyl-L-cysteine and S-allyl-L-cysteine, are known to suppress increasing levels of cholesterol in blood and liver. S-carboxymethyl-L-cysteine (SCC) is of pharmaceutical interest since it has mucous dissolving properties. Viscous mucous is rendered thin liquid by SCC and can thereby be more easily eliminated by coughings. SCC therefore is used for the production of medicines for treatment of bronchitis, tuberculosis, asthmatic illnesses as well as inflammations in the region of the throat and windpipe. In all organisms, L-cysteine occupies a key position in sulfur metabolism and is used in the synthesis of proteins, glutathione, biotin, methionine and other sulfur-containing metabolites. L-cysteine acts as a precursor in the biosynthesis of coenzyme A; in addition to this, L-cysteine can readily be oxidized to cystine. A close connection exists between the biosynthesis of L-cysteine and that of other amino acids such as L-serine, glycine and L-methionine. Cysteine proteases are involved in diverse cellular processes ranging from the processing of precursor proteins to intracellular degradation. They may induce vascular permeability through activation of the kallikrein/kinin pathway, complex with various hemagglutinins, activate complement components and destroy serpins. L-cysteine and its derivatives are employed in the pharmaceutical sphere (treatment of bronchial diseases), in the cosmetics sector (as constituents of hair shampoos and permanent wave lotions) and in the foodstuffs sphere (as antioxidants, as flavor enhancers and as adjuvants in the working of the dough). L-cysteine is an unstable compound which is easily oxidized. Therefore, it is usually sold in the form of its hydrochloride. L-Cysteine and its hydrochlorides are mainly used as medicines or materials for medicines, or additives to foods or cosmetics. The use thereof for preparing a cold-wave solution has recently shown a particularly great increase.

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