| Abstract: | The conformational transitions of synthetic basic polytripeptides (Lys-Leu-Gly)n, (A2bu-Leu-Gly)n, (Lys-Leu-Ala)n, and (A2bu-Leu-Ala)n induced by high salt concentrations and elevated pH were investigated by CD, ir, and 1H-nmr spectroscopy, sedimentation analysis, viscometry, and light scattering. Sheet aggregates of chains in a conformation similar to the polyglycine II (polyproline II) helix, bound together by hydrogen bonds, are the most probable form of (Lys-Leu-Gly)n and also, partly, of (A2bu-Leu-Gly)n in a high-pH or high-salt solutions. The conformation (Lys-Leu-Ala)n, in a low-salt concentration, is an α-helix. Since (A2bu-Leu-Ala)n is disordered under similar conditions, it appears that this α-helix is stabilized by hydrophobic interactions between Lys and Leu side chains. In a high concentration of water structure-making ions, CD data for (Lys-Leu-Ala)n indicate distortion of the α-helix, with a parallel increase in the average molecular weight corresponding to trimer formation. Hydrodynamic data are consistent with a model of bundles of three closely touching spherocylinders. (A2bu-Leu-Ala)n shows a limited tendency to α-helix formation. |
