Studies of self-association and conformation of peptides by thin-film dialysis

Abstract

The tyrocidine antibiotic polypeptides are known to exhibit self-association. They were therefore used as test substances to document the behavior to be expected by the method of thin-film dialysis. Self-association with these peptides is indicated by concentration dependence, a reverse curvature of the escape plot, and a retardation of the rate of diffusion by addition of salt but an acceleration by the addition of ethanol or other hydrophobic bond breaking solvent additives. A survey of dipeptides by thin-film dialysis has revealed that L-lysyl-L-lysine, L-lysyl-L-arginine, and L-histidyl-L-histidine exhibit a behavior characteristic of self-association in a pH region where all the acidic and basic T A he so-called quaternary structures of proteins and nucleotides are thought to result from the interplay of various binding forces such as hydrophobic bonds, coulombic forces, 7r bonds, and hydrogen bonds. The contribution of each individual interaction or small section of the molecule is considered to be relatively weak as compared with most covalent bonds but their sum in concerted effect can be strong. Such a theory agrees well with experience but leaves much to be understood about the detailed nature of each type of interaction and its contribution to the whole. A truly clear understanding is made uncertain by the many variables

Thin‐film dialysis rates of peptides. A relationship between half‐escape times and molecular weights

“…tides, recently reported by BURACHIK et al 1) it is shown in this paper that the half-escape times are linearly related to the cube root of the molecular weights of the peptides. The slopes of the two lines defined respectively by the alanine and the glycine peptides differ s m c a n t l y , and the fact that data points obtained for various composite dipeptides and for the alanine amino acid fall on the line defined by the glycine peptides indicates an exceptional diffusion behavior of the alanine peptides.…”

“…It may be added that it was evident already from one of the correlations suggested by BURACHIK et al 1) that the alanine amino acid could not be easily aligned with the alanine peptides (Fig. With 2 R as the diffusional diameter the equation would define a linear relation between diffusion rates and the cube root of the molec-Thin-Film Dialysis Rates of Peptides ular weight for the molecules in question But the equation cannot be applied to the results of BURACHIK et al 1) without qualifications, among which the most serious may be t h a t it is expected not t o hold for solute molecules with a molecular weight less than about 1000. That the test points for the longest axes could not be fitted to a straight line was in fact due t o the point arising from measurements on the amino acid.…”

“…BURACHIK et al 1) pointed out that their data ( Fig. 1) allow interesting comparisons concerning diffusional size when the longest axis is taken as the effective diffusional diameter.…”

“…1) for possible additional correlations between the dialysis rates and characteristics of the peptides and amino acids. 1) for possible additional correlations between the dialysis rates and characteristics of the peptides and amino acids.…”

Density, Viscosity and Dielectric Constant of Aqueous Solutions of Triglycine and Tetraglycine

“…Therefore it is unexpected that the E values of triglycine and tetraglycine are so similar. According to Craig et al [16] polyglycine chains must be more flexible than other polypeptides because of the absence of side chains and strong steric hindrance and, on the basis of spectroscopic data, Destrade et al [17] proposed a torsional conformation stabilized by intramolecular hydrogen bonds for diglycine and triglycine in water. It may therefore be supposed that our two peptides tend to adopt a spherical shape, reducing the contact surface with the surrounding water molecules.…”