The chemistry of connective tissues. 3. Composition of the soluble proteins derived from elastin

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Abstract
Amino acid analyses are given for purified elastin from ligamentum nuchae of cattle and for the [alpha]- and [beta]-proteins derived from it by mild acid hydrolysis (Partridge et al. 1955). The amino acid composition of the intact fibrous protein is regarded as substantially homogeneous. The glucosamine and galactosamine content of purified elastin was estimated by a chromatographic method; the 2 amino sugars together account for not more than 0.1% of the dry protein. The UV absorption spectra of the mixture of soluble proteins derived from elastin show the presence of an unidentified substance with an absorption peak in the region of 2750 A. N-Terminal groups in elastin and the 2 derived proteins were estimated by the fluorodinitrobenzene technique. Elastin contains 0.29 mole of N-terminal residues in 100,000 g, the [alpha]- and [beta]-proteins contain 24.4 and 32.5 moles of N-terminal residues respectively in the same weight of protein. It is deduced that the [beta]-protein has, as a mean value, 17 such chains containing 35 residues each. The nature of the crosslinks binding adjacent peptide chains in elastin and the 2 soluble proteins is discussed. The action of pancreatic elastase on purified elastin has been studied. It is concluded that dissolution of the fibrous protein is brought about by the rupture of peptide links and the active enzyme must be regarded as proteolytic.