Conformational changes of poly(L‐histidyl‐L‐alanyl‐α‐L‐glutamic acid) in solution. Transition pathways and conformational intermediates

Abstract

AbstractThe conformation and conformational transitions of poly(His‐Ala‐Glu) have been investigated by ir, nmr, and CD measurements. The results obtained—as well as the results of our previous investigations by potentiometric titration and hydrodynamic techniques [Goren et al., Biopolymers (1977) 16, 1541–1555]—indicate that when dissolved in water, the co‐polymer assumes a disordered conformation. On changing the pH of the solution, the states of ionization of the side‐chain imidazole and carboxyl groups change in the same manner as in low‐molecular‐weight model compounds. Concomitantly, the overall shape of the macromolecule is altered, while the conformation of the polypeptide backbone changes from one disordered state to another but never assumes a regular form. In water/methanol and water/trifluoroethanol mixtures, transitions from a disordered state to the α‐helix conformation were observed on increasing the alcohol content of the system. The conformational transitions followed pathways which differ from one another according to the experimental conditions employed. Conformational landmarks (intermediates) have been identified along these pathways.