Role of hydrophobic interactions on the stabilisation of native state of globular proteins

The technique of intensity photon correlation spectroscopy has been utilise d to investigate the native conformation of lysozyme in water/ethanol mixtu re as a function of alcohol concentration in the water-rich region of compo sition (cosolvent mole fraction x(2) < 0.08). A non-trivial behaviour of th e hydrodynamic radius is obtained, characterised by a minimum at x(2) = 0.0 2 and a maximum at x(2) = 0.06. This behaviour is similar to that of partia l molar volume of ethanol in water and reflects changes in the alcohol/wate r structure. The results are discussed in connection to the effect of alcoh ol in modulating solvent-mediated interactions. (C) 2000 Elsevier Science B .V. All rights reserved.