Effect of 1-alkanols on the native conformation of lysozyme

The technique of intensity photon correlation spectroscopy was utilised to investigate the native conformation of lysozyme in water-ethanol and 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 behaviour of the hydrodynamic radius was obtained, characterised by a minimum at x(2)=0.02 in water-ethanol and x(2)=0.005 in water-tert-butanol mixtures. This behaviour is similar to that of the partial molar volume of 1-alkanols in water and reflects changes in alcohol-water structure. The results are discussed in connection with the effect of the alcohol in modulating solvent-mediated interactions.