Statistical thermodynamic treatment of conformational transitions of monomeric and oligomeric proteins

The conformational transitions of monomeric and oligomeric proteins as mani fested in the heat capacity changes associated with thermal unfolding were quantitatively analysed on the assumption that proteins can be treated as m embers of a canonical ensemble. This treatment permits the calculation of t he partition function Y(T, p) relative to the native state. The second deri vative of Y(T, p) with respect to temperature represents perfectly the expe rimental heat capacity curve of the protein. The proper analysis of the sta tistical thermodynamic model results in an intriguing phenomenon for all tr ansitions except for the simplest case N reversible arrow D:the proportiona lity between the enthalpy and the population shift is lost. It is shown tha t this phenomenon can be both rationalised theoretically and verified exper imentally for the N-2 reversible arrow 2D transition of the protein ROP.