Modification of arterial elastin in vivo. Effects of age and diet on changes in the N-terminal amino acid content of aorta elastin.

We have previously demonstrated that aorta elastin, a highly crosslinked protein, does not undergo turnover that is easily measured in vivo. Therefore, it was hypothesized that when proteolysis of elastin occurs, a positive increase in N-terminal amino acids should result. Such an increase would represent elastin-derived fragments held covalently in situ. A cyanate carbamylation procedure was used to estimate the changes in N-terminal amino acids in aorta elastin. To provide tissue for the studies, Japanese quail (3 weeks old) were fed diets with or without the addition of 1% cholesterol. It was found that, in normal birds, the number of N-terminal amino acid residues increased from two to approximately three residues per 800 total residues (or mole of tropoelastin) throughout sexual development (3 to 8 weeks, post-hatching), with little increase thereafter. In hypercholesterolemic birds, the rate of appearance of new N-terminal residues, particularly glutamine or glutamic acid, appeared enhanced throughout early development, but by sexual maturity the number of N-terminal amino acid residues in aorta elastin from cholesterol-fed birds was similar to that for the control birds. For each of the elastin samples analyzed, approximately one residue of glycine was recovered per 800 total residues. Other amino acids that predominated as N-terminal residues were serine, aspartic and glutamic acids.