Preferential Hydration of Bovine Serum Albumin in Polyhydric Alcohol-Water Mixtures1

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Abstract
The preferential solvent interaction with bovine serum albumin in aqueous solutions of polyhydric alcohols (ethylene glycol, glycerol, xylitol, sorbitol, mannitol, and inositol) was investigated by a densimetric method with the application of multicomponent theory. This protein was preferentially hydrated in all solvent systems examined: the extent depended on the number and the steric configuration of the hydroxyl groups of alcohols. The absolute interactions of these alcohols with the protein were estimated by assuming that the amount of hydration of protein at every solvent composition used is identical with that in pure water. The preferential hydration of the protein in 30% aqueous solutions of glycerol and sorbitol was found to decrease as the temperature was increased, indicating that the increase in chemical potential of protein on transferring it from water to both aqueous solvents is generated by a large positive enthalpy change, sufficient to compensate for the positive entropy change in the transfer process. On the basis of these results, the mechanism of stabilization of protein structure by these alcohols was discussed from the viewpoint of the solvation of protein.