Ageing of Elastic Tissue 



95 



most of that from old individuals settled to the l^ottom. A 

 sample of the suitably washed light fraetiou (young light) 

 was prepared from several young aortas and some of the 

 heavy material (old heavy) was prepared from old aortas. 

 Both of these materials were analysed for calcium and the 

 contents of 18 amino acids. 



Table I 



Percentage of Principal Amino Acids in Purified Elastin from Aorta 



♦Significant increase. 



In Table II are shown the contents of 18 amino acids in the 

 light fraction of young aortic elastin and the heavy fraction 

 of old aortic elastin prepared by suspension in sucrose in the 

 manner described previously. In the case of the 7 amino 

 acids which were determined on whole elastin (Table I), the 

 differences observed between the young light and old heavy 

 fractions were all similar to those found for the young and old 

 whole elastin. The old heavy elastin show^ed increases in 

 aspartic and glutamic acids and decreases in the contents of 

 glycine, proline, and valine. There ^was also an increase in the 

 number of free carboxyl groups in the old heavy sample. In 

 addition, there was a decrease in the content of alanine. All 

 of the other amino acids showed increases of varying degree 

 in the old heavy elastin. Approximately 90 per cent of the 

 nitrogen of both samples was accounted for by the analyses. 

 The light fraction contained 1-14 per cent calcium while the 

 heavy fraction contained 6-39 per cent. 



