VIII.—Electron Microscopic Study and Amino Acid Analysis on Human Aortic Elastin

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Abstract
Human aortic elastin, purified by autoclaving and alkaline extraction, has been resolved by ultrasonic treatment into individual filaments, which appear, in the electron microscope, to be of constant diameter (25 Å) with junction points at fairly regular intervals (1300)Å.Amino acid analyses on fœtal, normal and old adult elastin showed that the desmosine(s) content remains constant at 3 residues per 105g. of protein which is equivalent to 1100 Å intervals between successive residues, assuming that these are evenly spaced along the polypeptide chain(s). On the other hand the amino acid composition was found to change with age. Thus the aspartic acid and glutamic acid contents increase from 3 and 19 to 11 and 27 residues respectively; histidine and methionine, which are both absent from fœtal elastin are present in small but definite amounts (2 and 3 residues respectively) in older elastins. The lysine content is 9 residues in fœtal elastin and 6 residues in older elastin. Probably the most remarkable feature of this protein is the high content of non-polar amino acids; of 1100 residues in 105g. protein about 1000 (including glycine and proline) have hydrophobic side chains.