Temperature-induced conformational changes of native lysozyme in aqueous solution studied by dielectric spectroscopy

We report dielectric measurements at radiofrequencies on lysozyme in aqueou s solution at two values of pH (3.5 and 6) as a function of temperature in the interval 5-55 degrees C. From the analysis of the dielectric relaxation of the protein solution, the effective hydrodynamic radius r and the elect ric dipole moment mu of the protein were calculated. The results show that temperature causes continuous gradual changes of r and mu with a maximum at 25-30 degrees C where the Gibbs free energy for native lysozyme shows an a nalogous trend. We suggest that the gradual variations of r and mu are the manifestation of a redistribution of microscopic state populations of the p rotein within the same macroscopic native state. (C) 1999 Elsevier Science B.V. All rights reserved.