Synthetic polypeptides cross-linked

The investigations presented focus on interpretation of polarization of fluorescence measurements and use of these measurements to study the structure of a representative spectrum of linear synthetic polypeptides, a vinyl polymer, and an intramolecularly cross-linked synthetic polypeptide. The methodological studies investigate the validity of the transition temperature as a structural parameter, the interaction of the fluorescent dye and the polymer to which it is conjugated, and the influence of the dye-polymer interaction on the measurements of various molecular parameters. The structural studies focus on the structure of the random coil, the helix-coil transition, the a-helix to conformation transition in polylysine, and the stability of the spatial structure in intramolecularly cross-linked synthetic polypeptides. 

These studies begin to provide a systematic basis for the detailed interpretation of polarization of fluorescence measurements in structural terms as well as hydrodynamic data about a wide range of linear and cross-linked synthetic polypeptides. The further development of such studies will provide a firm basis for applying polarization of fluorescence techniques to the study of the structure of native proteins in solution. 

Table IX. Polarization of Fluorescence Parameters and Intrinsic Viscosities of Cross-linked Synthetic Polypeptides and Their Parent...

The internal structure of the cross-linked synthetic polypeptides is maintained by heat-stable, covalent bonding between the cross-linked amino acid side chains and by heat-labile, noncovalent side chain interactions between glutamic acid and lysine residues (electrostatic) and between tyrosine residues (nonpolar). The stability of the spatial structure of a polymer depends upon the relative proportion of covalent and noncovalent bonding that it contains and increases as the number of cross-links increases. According to the current theories of protein structure, the charged amino acid residues would be arrayed on the surface of the molecule, and the tyrosine residues would be internally placed and thus interact to give a hypochromic effect. Am(6)-poly Glu52Lys33Tyr15 (No. 3B) (Fr. 1) displays such an effect, and the molar extinction coefficient of the cross-linked derivative is 25% lower than that of the parent polymer. This hypo-... 

The investigations presented in this study focus on the interpretation of polarization of fluorescence measurements and the use of these measurements to study the structure of a representative spectrum of linear synthetic polypeptides, of polyvinylamine, and of a cross-linked synthetic polypeptide. 

A polymer is a macromolecule that is constructed by chemically linking together a sequent of molecular fragments. In simple synthetic polymers such as polyethylene or polystyrer all of the molecular fragments comprise the same basic unit (or monomer). Other poly me contain mixtures of monomers. Proteins, for example, are polypeptide chains in which eac unit is one of the twenty amino acids. Cross-linking between different chains gives rise to j-further variations in the constitution and structure of a polymer. All of these features me affect the overall properties of the molecule, sometimes in a dramatic way. Moreover, or... 

What accommodations, then, must be made in the pattern of analysis developed for standard synthetic polypeptides if it is to yield quantitative estimates of partial helical content in proteins The requirements are much the same as those set out for poly-L-lysine (see Section III, G, 3), yet since globular proteins, like copolymers of L-lysine and L-glutamic acid, cannot be made completely helical in aqueous solution, a helical reference conformation must be taken either from other standard molecules or from the nonaqueous behavior of the protein in question. This latter procedure involves solvent changes with little bearing on native conditions and may be impossible to carry out in the face of restraints imposed by proline and cross-links, so that standard helical dispersion can more feasibly serve as this reference conformation. 

Introducing intramolecular amide bonds into synthetic polypeptides produces organized spatial structure which makes these polymers good models for the tertiary structure of proteins. The transition temperature, which measures the organized internal structure of the molecule, increases as the number of cross-links increases. The amount of internal structure has little effect on the over-all rigidity of the molecule until six cross-links have been introduced into the polymer. On the other hand, the over-all hydrodynamic domain of the molecule decreases to the same extent whether one, four, or six intramolecular cross-links are present. 

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