Biomedical subjects
Publications and source records attributed to D W Urry.
Electron micrographs of negatively stained coacervates of the synthetic polypentapeptide of propoelastin and of alpha-elastin exhibit banded fibers when the coacervates are formed, stained, and dried at temperatures greater than 50 degrees. This apparent increase in order occurs at the same temperature as an increase in order in aqueous solution and as a change in the volume expansion coefficient of fibrous elastin.
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Physical properties of the cross-linked polypentapeptide of tropoelastin are reported along with chemical characterization of key intermediates in its synthesis. 220 MHz proton magnetic resonance spectra are reported on the constituent pentamers and their respective high polymers which verify structural and conformational integrity. Scanning electron microscopy of the cross-linked material formed without orientation and with flow orientation is reported. The former demonstrates the inherent fibrillar and anisotropic nature of the synthetic product. Stress-strain studies show the cross-linked polypentapeptide to exhibit elastomeric properties that are dependent on the water content of the matrix. At high water contents the elastic modulus is less than that of wet native aortic elastin and becomes greater on drying.
The synthetic, cross-linked polypentapeptide of tropoelastin has been shown to calcify from serum alone even when separated from the serum medium by a dialysis membrane with a low-molecular-weight cut off. By microprobe analysis, it appeared that the only serum elements required for the calcification were calcium and phosphorus. Furthermore, thin sections of the calcified matrix showed the calcification to occur throughout the matrix, and thereby verified that it is a bulk property of the matrix and not an interfacial property. To our knowledge this is the first demonstration of an insoluble, synthetic polypeptide to function as a serum calcifiable matrix and by doing so it opens the door to potential medical applications.
Scanning electron microscopy and electron probe microanalysis studies are reported on thin sections of calcified coacervates of alpha-elastin. It is found that the capacity of elastin coacervates to initiate calcification is a bulk property of the coacervate and not limited to the serum-coacervate interface, that the calcium phosphate deposits act to bind the protein units together and slow the dissolution and spreading of the coacervate as it floats on an airwater interface, and that, within the limits of detectability, there is no involvement of sulfur. As the charged groups of alpha-elastin had been blocked, the initiation of deposition is due to neutral sites in the protein which are tightly bound to the calcium phosphate deposits.
Optical diffraction applied to micrographs of coacervated tropoelastin and alpha-elastin show an equatorial repeat around 50 A. This confirms a 50 A center-to-center distance of parallel aligned filaments to be a fundamental property of the tropoelastin and alpha-elastin coacervates. This periodicity is similar to that of mature cross-linked elastin. These results allow the conclusion that hydrophobic association is the predominant driving force for formation of filamentous elastin in vitro. It is suggested that the coacervate is a model for relaxed fibrous elastin.
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Repeat hexapeptides of elastin have been synthesized and studied with nuclear magnetic resonance methods. The deuterium substituted hexapeptide HCO-Ala1-Pro2-(2H2) Gly3-Val4-Gly5-Val6-OMe allowed completion of the proton assignments and specifically the definitive assignments of the Gly3 and Gly5 resonances. Solvent titrations followed by carbon-13 magnetic resonances are reported which delineate the Ala1 C-O and Gly5 C-O as intramolecularly hydrogen bonded. This coupled with the proton magnetic resonance data which delineated the Gly3 NH and VAL4 NH as candidates for intramolecular hydrogen bonding lead to the proposal of two hydrogen bonds, one between the Ala1 C-O and the Val4NH and the second between the Gly5C-O and the Gly3NH. The probability, or mol fraction, of occurrence of these secondary structural features is demonstrated to be high.