LYSOZYME-LYSOZYME INTERACTIONS IN UNDER-SATURATED AND SUPER-SATURATEDSOLUTIONS - A SIMPLE RELATION BETWEEN THE 2ND VIRIAL-COEFFICIENTS IN H2O AND D2O

A study of lysozyme-lysozyme interactions by small angle neutron scatt ering (SANS) as a function of temperature in D2O and in H2O is present ed. The interactions are analysed in terms of second virial coefficien t. The most remarkable result is that the difference between the tempe rature dependencies of this quantity in D2O and H2O seems similar to t he one we have previously observed for lysozyme solubility in these tw o solvents. These physicochemical quantities in D2O, the second virial coefficient and solubility, are indeed shifted by approximately 7.2 d egrees C relatively to the ones in H2O. This temperature shift, 7.2 de grees C, corresponds to the difference of the temperatures of maximum density of H2O (4 degrees C) and D2O (11.2 degrees C). The interaction s are modelled by the DLVO potential, which includes an attractive van der Waals component, proportional to the Hamaker constant A(H) and a repulsive screened electrostatic term, proportional to the net charge of the protein Z(p). The attractive component seems to phenomenologica lly account for effects due to the water structure, as the Hamaker con stant A(H) also appears to be shifted by about 7.2 degrees C.