Dynamics of the Helix—Coil Transition in Isotope Exchange of Polypeptide

Abstract

Isotope exchange experiments in the study of the helical conformation of a polypeptide suggest that the rate constant of the helix-coil change of a unit depends on its location and that it is very low in the central portion of the chain. In this paper, a model is presented to explain the low rate constant and its site dependence. When an inner residue in the helix state unwinds to the coil state, the entire helix should move in viscous medium. The mobility of unwinding in the complete helical polypeptide is calculated by the method of Kirkwood. As a result of this frictional effect, the transition rate constants obtained are in reasonable agreement with experimental results.