Circular dichroism investigations on the conformation of linear,cyclic and polymeric peptides containing His,Ser and Asp residues

Conformational studies on the linear, cyclic and polymeric peptides with the sequences -Asp-ßAla-Gly-Ser-ßAla-Gly-His-ßAla-Gly-(nonapeptide series) and -Asp-eAhx-Ser-eAhx-His-eAhx (hexapeptide series) were carried out by means of circular dichroism measurements to clarify the relationship between their conformation and ester hydrolytic activity. It was suggested that all of the present peptides take a certain ordered conformation at acidic pH region and have a tendency to transform to a disordered conformation with a rise of pH. In the course of the conformational change, the linear and polymeric peptides undergo a drastic conformational change at around pH 7.0, while the cyclic peptides maintain the ordered conformation to some extent even at the basic pH region. Although this ordered conformation maintained in the cyclic peptides was estimated not to be a tight one, it was more stable in the cyclic peptide of the latter sequence (Cyclic-6) than in the former sequence (Cyclic-9). As reported previously, Cyclic-6 showed greater activity than the others in the hydrolysis of various ester substrates. Higher activity and more stable ordered conformation of Cyclic-6 seem to be closely related. The effects of urea, organic solvent, salt and change of temperature on their conformation are also reported.