Isolation of elastin from bovine auricular cartilage

Abstract

Clostridium histolyticum collagenase (clostridiopeptidase A, EC 3.4.24.3), purified by affinity chromatography, was applied to the isolation of insoluble elastin from bovine auricular cartilage. The low level of N-terminal residues (2.8 mol per 10 6g of protein) present in this preparation indicated the almost complete lack of hydrolytic damage caused by the isolation procedure. The amino acid composition of the preparation showed an overall two-fold increase in polar residues, and a 20% reduction in valine, when compared to those of aortic and ligamentum nuchae elastin, while the concentration of cross-links was almost identical in the three preparations. Analysis of peptides, isolated by gel-exclusion chromatography after digestion of auricular elastin with elastase (pancreatopeptidase E, EC 3.4.21.11) in the presence of sodium dodecyl sulfate, revealed elevated levels of polar residues in all fractions examined, with no correlation between the concentration of these amino acids and that of the lysine-derived cross-links. Comparison of auricular and ligamentum nuchae elastin by fingerprint analysis of their elastase digests also suggested that the two proteins were compositionally distinct. Finally, treatment of auricular elastin with either trypsin or chymotrypsin produced no significant reduction in the level of polar residues. It is concluded that elastin exhibits tissue-related compositional variability.