Molecular dynamics of solid-state lysozyme as affected by glycerol and water: A neutron scattering study

Glycerol has been shown to lower the heat denaturation temperature (T-m) of dehydrated lysozyme while elevating the T-m of hydrated lysozyme (Bell, Ha geman, and Muraoka, 1995. J. Pharm. Sci. 84:707-712). Here, we report an in situ elastic neutron scattering study of the effect of glycerol and hydrat ion on the internal dynamics of lysozyme powder. Anharmonic motions associa ted with structural relaxation processes were not detected for dehydrated l ysozyme in the temperature range of 40 to 450K. Dehydrated lysozyme was fou nd to have the highest T-m by Bell et al. (1995b). Upon the addition of gly cerol or water, anharmonicity was recovered above a dynamic transition temp erature (T-d), which may contribute to the reduction of T-m values for dehy drated lysozyme in the presence of glycerol. The greatest degree of anharmo nicity, as well as the lowest T-d, was observed for lysozyme solvated with water. Hydrated lysozyme was also found to have the lowest T-m by Bell et a l. (1995b). In the regime above T-d, larger amounts of glycerol lead to a h igher rate of change in anharmonic motions as a function of temperature, re ndering the material more heat labile. Below T-d, where harmonic motions do minate, the addition of glycerol resulted in a lower amplitude of motions, correlating with a stabilizing effect of glycerol on the protein.