Conformational changes of lysozyme in water-ethanol mixtures

In this paper, we report dielectric spectroscopy and optical measurements on lysozyme in water-ethanol mixtures as a function of alcohol concentration in the water-rich region of composition (cosolvent mole fraction X~<0.25). Dielectric measurements show a well defined relaxation curve in the MHz region, from which we obtain the electric dipole moment # and the effective hydrodynamic radius r of the protein. UV melting measurements with estimation of the van't Hoff enthalpy are also reported. Molar ellipticity measurements were performed to test the or-helix content. The results indicate that alcohol promotes a more tightly folded conformation of the protein. Our measurements show a correlation between the effects of ethanol on the conformational properties of lysozyme and changes in the properties of solvent, as inferred from previous adiabatic compressibility and IR data on water-ethanol mixtures.