  We present a novel statistical mechanics formalism for the theoretical
description of the process of protein folding$\leftrightarrow$unfolding
transition in water environment. The formalism is based on the construction of
the partition function of a protein obeying two-stage-like folding kinetics.
Using the statistical mechanics model of solvation of hydrophobic hydrocarbons
we obtain the partition function of infinitely diluted solution of proteins in
water environment. The calculated dependencies of the protein heat capacities
upon temperature are compared with the corresponding results of experimental
measurements for staphylococcal nuclease and metmyoglobin.
