A non-essential amino acid in human development. Readily oxides to form a dimeric amino acid, cystine, q.v., in which the two Cys are linked via a disulfide bridge, a common structural feature in proteins. Early chemistry and biochemistry: Amino Acids and Proteins, D. M. Greenberg, Ed. (Charles C. Thomas, Springfield, IL, 1951) 950 pp., passim; J. P. Greenstein, M. Winitz, Chemistry of the Amino Acids vol 1-3 (John Wiley and Sons, Inc., New York, 1961) pp. 1879-1928, passim. Simple synthesis of racemic cysteine: V. J. Martens et al., Angew. Chem. Int. Ed. 20, 668 (1981). Determn in proteins: J. G. Hoogerheide, C. M. Campbell, Anal. Biochem. 201, 146 (1992); D. Atherton et al., ibid. 212, 98 (1993). Review of biosynthesis: N. M. Kredich et al., Ciba Found. Symp. (Netherlands) 72, 87-99 (1980). Review of transport in mammalian cells: S. Bannai, Biochim. Biophys. Acta 779, 289-306 (1984). Review of effects on acrylonitrile toxicity: D. E. Nerland et al., Drug Metab. Rev. 20, 233-246 (1989). Review of thermodynamics and kinetics: T. R. Ralph et al., J. Electroanal. Chem. 375, 1-15 (1994); of electrosynthesis: eidem, ibid. 17-27. Review of role in chemo- and radioprotectant strategies: J. C. Roberts, Amino Acids 8, 113-124 (1995).