X-RAY DIFFRACTION STUDIES OF HUMAN AORTIC ELASTIN RESIDUES*

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Abstract
Elastin residues from human aortas have been prepared on the basis of their insolubility in water at autoclave temperature. The crystallites associated with such residues became prominent in aortas from older individuals and were identified as hydroxyapatite by X-ray diffraction analysis. In aortas obtained from young subjects, only a diffuse X-ray scattering characteristic of protein was observed; this scattering decreased with advancing age. These X-ray findings paralleled a decrease in N and an increase in Ca content of isolated aortic elastin residues with advancing age. The intimate structural association of hydroxyapatite crystallites with elastin in aortic tissue has been demonstrated by means of elastase. Treatment of elastin residues with this enzyme caused the liberation of a protein into the non-dialysable supernatant solution of the digestion mixture, which, upon ethanol precipitation, gave the typical diffraction pattern of hydroxyapatite. Neither collagen nor polysaccharide fractions obtained from human aortas exhibited crystalline patterns,.