The chemistry of connective tissues. 2. Soluble proteins derived from partial hydrolysis of elastin

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Abstract
Elastin from ligamentum nuchae of cattle is transformed into a soluble protein by repeated extraction with 0.25 [image] oxalic acid at 100[degree] with the loss of about 5% of the N as small peptides. The protein is soluble in distilled water or buffer solutions at temperatures below 25[degree], but on raising the temperature of the solution in dilute buffer at pH 4-6 a precipitate consisting of liquid droplets separates. The protein shows a single boundary peak in the Tiselius electrophoresis apparatus in buffers of ionic strength 0.20 at all pH values in the range pH 2-9. At ionic strength 0.2 the pH values for the isoelectric point from electrophoretic mobility measurements and from membrane potential determinations are 3.9 and 4.0, respectively; at ionic strength 0.02 the values are 4.8 from electrophoresis measurements and 4.7 from membrane potentials. Fractionation of the soluble protein shows it to consist of 2 components with markedly different physical properties; the major component (a-fraction) shows the characteristic property of reversible coacervate formation on heating and has a mean molecular weight of 60,000-84,000 in different preparations, while the minor component ([beta]-fraction) is soluble in water at all temperatures and has a mean molecular weight of 5500. Further fractionation and investigation with the ultracentrifuge suggests that the a-protein is itself poly-disperse. The [alpha]- and [beta]-proteins are liberated at different rates during the extraction of elastin powder. The bearing of these results on the structure of the native fibrous protein is discussed.