Study of protein-protein interactions in undersaturated and supersaturated lysozyme solutions in heavy water as a function of temperature

We have studied freshly prepared lysozyme solutions in heavy water for two NaCl concentrations as a function of temperature. Lysozyme solubilities in this solvent are determined by static light scattering. By small angle neutron scattering, we evidence that interactions between lysozyme molecules are characterized by a second virial coefficient A(2) whether the solution is undersaturated or supersaturated. From the Variation of A(2) as a function of temperature we have evaluated the enthalpy corresponding to the interaction between lysozyme molecules. We show that the interactions between protein molecules are higher in heavy water than in light water.