DETERMINATION OF HYDROPHOBIC HYDRATION IN PROTEIN UNFOLDING BY AN INTRINSIC REFERENCE STATE

This paper describes a method for the evaluation of the unfolding heat capacity change of proteins by their amino-acid composition. The meth od hinges on a set of hydration heat capacity changes of amino acids e xtracted from the Protein Data Bank of crystallographic structures (Oo batake, M. and Ooi, T. (1988) J. Biochem. (Tokyo) 104, 433-439). This avoids problems linked to the choice of an arbitrary reference state. The published values have been normalized with respect to the total su rface area of each amino-acid residue and related to the non-polar sur face. The relationship found for amino acids allows a straightforward estimate of the unfolding heat capacity change of globular proteins. P redicted values for a large set of proteins fall within the experiment al error. The devised algorithm shows that the unfolding heat capacity change depends on chain length and provides an explanation for the ph ysical limits imposed upon this quantity.