Statistical-Mechanical Approach to the Thermodynamic Functions in the Unfolding of Biomolecules

Abstract

Our statistical-mechanical formulation for calculating heat-capacity and enthalpy functions in conformational changes of biomolecules is extended to include free-energy and entropy functions and generalized to treat multidomain systems. Each conformant may consist of one or several independent sections or domains. The treatment is based on a two-state model in which all residues within a domain are fully cooperative. The thermodynamic functions can be evaluated from the ratio of the effective partition functions of the residues in the different conformants, the difference in their zeros of energy, and the temperature derivatives of these partition functions. The former two parameters were evaluated from published optical density data of the conformants within the transition region; the last item was obtained from published heat-capacity data of the pure conformants outside the transition region. Three types of thermodynamic functions were considered: (1) total functions, which include contributions from ...