Dimensional Properties of Polypeptides in the Helix–Coil Transition Region II. Intrinsic Viscosity

Abstract

The theory presented in the preceidng paper (Part I) for the molecular dimensions, ‹s2›oI and ‹s2›I, of polypeptides in the helix–coil transition region is applied here to determine the intrinsic viscosity [η]I, (the [η] in the transition region) as a function of the helical content fH which varies with the cooperativity parameter (eq I-16). Using the Kurata–Yamakawa theory, the linear expansion factor αs was converted to the hydrodynamic expansion factor αη Thus, with αηI, (the αη in the transition region) and ‹s2›oI (eq I-10), the [η]I’s of polypeptides in the helix–coil transition region were calculated (eq 3), and compared with experimental results for various kinds of polypeptide–solvent systems with good agreement (Figures 3 and 4).