Molecular events such as cis/trans isomerization of Xaa-Pro tertiary amide bonds in peptides and proteins are slow on the overall time scale of the formation of a final biostructure and are, therefore rate limiting. In order to pursue a better understanding of the molecular events underlying such slow interconversions, Lee applied the recently introduced pseudo-proline (Psi Pro) concept as a tool to study the dynamics of Xaa-Pra bands by determining the kinetics and thermodynamics of cis/trans isomerism. We show that enhanced isomerization rates of tertiary amide bonds prior to a Psi Pro unit in shout model peptides is due to lowered transition state barriers. In addition, pronounced effects upon the dynamics of the reversible transition between helix I and II of oligoprolines containing one or sever-nl Psi Pro units were observed. (C) 1999 John Wiley & Sons, Inc.