Low-temperature heat capacity of biomacromolecules and the entropic cost of bound water in proteins and nucleic acids (DNA)

On the basis of the heat capacity data for proteins and DNA, obtained in the wide temperature range (2-300 K), the amount of the entropic cost of bound water in biomacromolecules is determined. The entropic cost of transferring a single water molecule from the liquid to a site of biopolymers is: 66.9, 58.1, 10.4 and 15.5 J mol(-1) K-1 for fibrous protein (collagen), nucleic acid (double helical DNA), globular protein (Ribonuclease A), desoxynucleotides (d(AMP), d(TMP), d(GMP), d(CMP)) mechanical mixture and DNA polynucleotide chains in the state of statistical coils, respectively. These correspond to transfer-free energy costs as follows (at 298 K): 19.15, 17.5, 3.7 and 4.6 kT mol(-1), respectively. We emphasize that the transfer entropy values determined here are not to be confused with the "entropy of hydration" of polar and nonpolar groups in biopolymers, which are relevant to the thermodynamics of protein folding or DNA double helix winding-unwinding. (C) 1998 Published by Elsevier Science B.V.