The Effect of Polyhydric Alcohols on the Thermal Denaturation of Lysozyme as Measured by Differential Scanning Calorimetry

Abstract

Abstract The thermal denaturation of lysozyme in aqueous solutions of polyhydric alcohols at pH 2 was investigated by differential scanning calorimetry (DSC). The polyhydric alcohols employed were inositol, sorbitol, xylitol, erythritol, glycerol, and ethylene glycol. These alcohols tended to enhance the thermal stability of lysozyme; both the temperature and the enthalpy of denaturation increased almost linearly with increasing alcohol concentration. The increase in denaturation temperature at a given alcohol concentration was a linearly increasing function of the number of hydroxyl groups per alcohol molecule. The denaturation enthalpy at identical temperature increased only slightly by the addition of polyhydric alcohol. The hypothesis may be supported that the dominant mechanism by which polyhydric alcohols stabilize proteins to thermal denaturation is through their effect on the water structure, which determines the strength of the hydrophobic interactions between the nonpolar groups of the protein.