Structural Studies on Cross-Linked Regions of Elastin

A novel use of Edman degradation was made in the study of desmosine- and isodesmosine-containing elastolytic peptides of bovine ligamentum nuchae elastin. The elastolysis of elastin produced peptides with the cleavage at or near the NH2-terminals of desmosine and isodesmosine cross-links. Therefore, it became possible to release single chain peptides from the carboxyl groups of these cross-links with the use of Edman degradation. This approach permitted the isolation and sequencing of seven unique peptides from bovine ligamentum nuchae elastin; the sequences of five such peptides from porcine aortic elastin were also determined. The comparison of the sequences of these peptides with the NH2-terminal sequences of porcine tropoelastin tryptic peptides (Foster, J. A., Bruenger, E., Gray, W. R., and Sandberg, L. B. (1973) J. Biol. Chem. 248, 2876–2879) permitted the identification of 12 possible lysine sequences which may be involved in cross-link formation. On the basis of the available data on elastin and tropoelastin, it is proposed that the tropoelastin molecule contains six pairs of lysines in the sequence -Lys-Ala-Ala-Lys- and six additional pairs of lysines in the sequence -Lys-Ala-Ala-Ala-Lys- and that two such pairs meet to form desmosine or isodesmosine cross-links.