Conformational changes of proteins in aqueous solution induced by temperature in the pre-melting region

In this paper we report dielectric measurements at radiofrequencies on aqueous solutions of three proteins (cytochrome, lysozyme and metmyoglobin) in the native state as a function of temperature in the interval 0-60 degreesC. From the analysis of dielectric relaxation of the protein solutions, the effective hydrodynamic radius r and the electric dipole moment mu of the proteins were calculated. The results show that temperature causes continuous gradual changes of r and mu, with a maximum at a temperature that is different for each protein. This effect in the pre-melting region seems to be general and related to variations of thermodynamic parameters.