Elastin is the insoluble, elastic protein of high tensile strength found in intercellular spaces of the connective tissues of large arteries, trachea, bronchi and ligaments. It has been reviewed by Seifter and Gallop (1966). Elastin consists of covalently cross-linked polypeptide chains "randomly kinked" (Sykes and Partridge 1972). Although it is characterized by non-polar amino acid residues it has an affinity for calcium ions. Urry (1971) has indicated that calcification of aortic elastin may be the start of chronic arteriosclerosis. See also Hornebeck and Partridge (1975), Abatangelo, et al. (1974), Urry et al. (1971). The polypeptide structural units are linked by two novel amino acids: desmosine and isodesmosine (Davis and Anwar 1970; Shimada et al. 1969; Thomas et al. 1963). The soluble, unlinked polypeptides (tropoelastin) are obtainable (Smith et al. 1968). According to Sykes and Partridge (1972) the cross-bonding involves oxidative deamination of lysine residues - a reaction inhibited by Cu2+ deficiency and lathyrism. See also: Foster et al. (1975), Narayanan et al. (1974), Sandberg et al. (1971 and 1969). Petruska and Sandberg (1968) report on the amino acid composition of soluble and insoluble elastin and indicate a minimum M.W. of 30,000; Smith et al. (1972) report it to be 74,000 using pig aorta. Robert et al. (1971) report a varying proportion of glycoprotein. See also Long et al. (1975), Lyerla and Torchia (1975), Castellani and Nolpin (1974), >Urry et al. (1974), Cox et al. (1973), Starcher et al. (1973), Beevers (1971), Grant et al. (1971). Gerber and Anwar (1975) report that bovine aortic and ligamentum nuchae elastins have identical sequences. See also Steven and Jackson (1968). Dorrington et al. (1975) and Gray et al. (1973) report on its elasticity. Another characteristic is fluorescence activated by ultraviolet light. See Thornhill (1975). Kakivaya and Hoeve (1975) indicate that the glasslike rigidity that occurs on heating is related to its H2O content. Elastin is not hydrolyzed by trypsin, chymotrypsin or pepsin but it is acted upon by plant proteases: bromelin, ficin and papain (Seifter and Gallop 1966) and some from microbial sources (Suss et al. 1969); Morihara and Tsuzuki 1967; Morihara et al. 1965). Keller and Mandl (1971) report on the determination of elastolytic activity.