CHARACTERIZATION OF INSOLUBLE ELASTIN FROM COPPER-DEFICIENT PIGS - ITS USEFULNESS IN ELASTIN SEQUENCE STUDIES

Insoluble elastin from Cu-deficient animals has an amino acid composition intermediate between mature elastin and salt-soluble elastin (a higher lysine content and correspondingly low number of cross-links relative to the normal protein) and is solubilized by successive treatment with trypsin and chymotrypsin at 4 and 37.degree. C. Small amounts of B3H4 (11 mg-2 g of elastin) reduced allysine, allysine aldol, dehydronorleucine and dehydromerodesmosine in insoluble elastin from Cu-deficient pig aorta. In contrast, desmosine and isodesmosine were reduced only when a large excess of reductant (400 mg borohydride) was included in the reaction mixture. Reduction studies indicated that lysinonorleucine and merodesmosine were present in their dehydro forms to a greater extent in Cu-deficient pig elastin than in normal elastin. After reduction with borohydride approximately 35% of the reduced form of the insoluble elastin remained insoluble after digestion with trypsin and chymotrypsin. A peptide containing the aldehyde oxidation product of lysine (allysine) and demonstrating an enrichment in glutamic acid was purified from the reduced form of Cu-deficient pig elastin and partially sequenced. Its sequence (Gly-Ala-Glu-allysine-(Glu)...) and amino acid composition suggest: clustering of glutamic acid residues in the elastin molecule, and that allysine residues are not restricted to the alanine-enriched sites described for other elastin cross-links. Insoluble elastin from Cu-deficient animals promises to be a useful tool for elastin sequence studies.