d· Ala5 analog of the elastin polypentapeptide. Physical characterization

Abstract

The D .cntdot. Ala5 analog, (L .cntdot. Val1-L .cntdot. Pro2-Gly3-L .cntdot. Val4-D .cntdot. Ala5)n, of the polypentapeptide (PPP) of elastin [pig, chick] is synthesized and characterized by a series of physical methods. 13C and proton NMR spectroscopies are used to verify purity and, by means of solvent dependence of peptide C-O chemical shift and of temperature dependence of peptide NH chemical shift, to establish by comparison with the PPP of elastin the presence and increaseed stability of the type II Pro2-Gly3 .beta.-turn. The temperature dependence of aggregation in H2O to form a viscoelastic phase called the coacervate is reported for several concentrations. Comparison of 13C NMR spectra obtained under identical conditions for the coacervate states of the PPP of elastin and the D .cntdot. Ala5 analog shows the effect of replacing the Gly5 residue by a D .cntdot. Ala5 residue to be one of greatly restricting mobility of the polypeptide chain. Scanning electron micrographs, of the coacervate alone and of the coacervate cross-linked and compounded to a Dacron fabric before and after stress-strain studies, are reported which show the D .cntdot. Ala5 PPP matrix to rupture during the stresses of drying and of stretching while wet. Thus, the effect of adding a methyl moiety to the Gly5 residue of the PPP of elastin is to decrease markedly the mobility of the polypeptide chain and to destroy elasticity. The results are presented as a test of the proposed librational entropy mechanism of elasticity of the PPP of elastin.