Conformational properties of <scp>L</scp>‐leucine, <scp>L</scp>‐isoleucine, and <scp>L</scp>‐norleucine side chains in <scp>L</scp>‐lysine copolymers

Abstract

Abstract The structure inducing properties of L ‐leucine, L ‐isoleucine, and L ‐norleucine residues incorporated into poly( L ‐lysine) were investigated by the observation of the circular dichroism of the respective random copolypeptides. The comparison involves the coil‐helix transition in water/methanol mixtures, the formation of ordered structures at higher pH, and the kinetics of the α‐helix to β‐conformation transition of the leucine and norleucine copolymers induced by temperature changes at pH 10.5. The results confirm the known properties of the leucine residue, strongly supporting the α‐helix conformation. They also support the idea that the isoleucine residue is one of the most powerful candidates for β‐structure formation, and they show that the unbranched norleucine residue has intermediate properties. The results are discussed on the basis of steric and hydrophobic properties of the three side chains.