Lysozyme solubility in H2O and D2O solutions: A simple relationship

We have determined the temperature dependence of the solubility of lysozyme in light water, heavy water and in a mixture 50% H2O/50% D2O for various NaCl contents at a given pH. For the solubility measurements, we have used a static light device that we have developed in the laboratory. We have found that the curves representing lysozyme solubility in light and heavy water are shifted by 7.2 degrees C, the difference in the temperature of maximum density of both types of water. As the density of light and heavy water are similarly shifted by 7.2 degrees C, we have plotted master curves, for a given NaCl concentration, of lysozyme solubility as a function of water density, The solubility data, in the 0.3-0.6 M NaCl range: show an equivalence between the effect of 0.1 M NaCl and the isotopic substitution of light water by heavy water. We propose that this equivalence could be explained by the same kind of influence of each effect on the water structure.