Examination by dynamic light scattering of lysozyme in water/alcohol mixtures

The technique of intensity photon correlation spectroscopy has been utilized to investigate the native conformation of lysozyme in water/ethanol and in water/tert-butanol mixtures as a function of alcohol concentration in the water-rich region of composition (cosolvent mole fraction x(2) < 0.08). A non-trivial behavior of the hydrodynamic radius is obtained, characterized by a minimum at x(2) = 0.02 and a maximum at x(2) = 0.06 in water/ethanol mixtures and by a minimum at x(2) = 0.005 and a maximum at x(2) = 0.02 in water/tert-butanol mixtures. These values of x(2) are close to those at which structural changes in the mixtures occur as inferred from compressibility and infrared absorption measurements. The results are discussed in connection to the effect of alcohol in modulating solvent-mediated interactions, (C) 2001 Elsevier Science B,V. All rights reserved.