94 Albert I. Lansing 



increases. The loss of arterial elasticity with age cannot be 

 attributed to a loss of elastic tissue. It is more likely due to a 

 change in the properties of elastic tissue with age. 



Amino acid composition of young and old arterial 

 elastin 



Microbiological assay of aortic and pulmonary elastin 

 prepared in the usual manner was effected by the method of 

 Roberts, Ramasarma and Lewis (1950). Nitrogen analyses 

 indicated a content between 15 and 16 per cent suggesting 

 that elastin is largely protein. Highly significant increases 

 in the contents of aspartic and glutamic acids were noted in 

 the samples of old aortic elastin as compared to those of the 

 young elastin, in confirmation of the chromatographic 

 findings. There were also increases in the contents of amide 

 nitrogen. However, there was a four-fold increase in the 

 excess of dicarboxylic acids over amide nitrogen, showing 

 that the quantity of free carboxyl groups was increased 

 significantly in the older specimens. The mean values for 

 valine, proline, and glycine contents were somewhat lower in 

 the older samples, while the leucine and isoleucine contents 

 in the two groups were closely similar. In contrast to the 

 findings for aortic elastin, the pulmonary elastin did not show 

 increases in aspartic and glutamic acid contents with age. The 

 other amino acids also did not change significantly. The 

 contents of the proline, leucine, isoleucine, and valine were 

 virtually identical with those found in young aortic elastin. 

 However, the contents of glycine and the dicarboxylic amino 

 acids were higher in the pulmonary elastin. The quantity of 

 free carboxyl groups was at least twice as great as that found 

 in young aortic elastin, while the range showed some overlap 

 with that of the old aortic elastin. It was found that a separa- 

 tion of fractions having differing specific gravities could be 

 achieved by differential centrifugation of finely ground 

 elastin (Wiley mill) in sucrose solution (sp.gr. 1 -30). Most of 

 the material in samples of aortic elastin from very young 

 individuals floated on the solution after centrifugation, while 



