Contribution of the Excluded Volume of Bovine Serum Albumin for Solute Molecules to the Apparent Nonsolvent Water

Addition of a macromolecule to a solution will give rise to a large excluded volume for the centers of the solute molecules. This will cause an apparent increase in solute concentration which is of the same order of magnitude as that associated with the nonsolvent volumes reported in the literature. A critical examination of one of the procedures used for the determination of nonsolvent water—the vapor pressure method of Hill—is given, and it is concluded that, with the use of this method, it is impossible to detect any significant nonsolvent water surrounding bovine albumin for either sugars or polyols. Generally, data reported in the literature for the nonsolvent water of proteins or other macromolecules will be too high unless they are corrected for the excluded volume.