Effect of Na+ and K+ ions on the initial crystallization process of lysozyme in the presence of D2O and H2O.

Abstract

In the initial stage of the crystallization of egg-white lysozyme, monomeric lysozyme aggregated rapidly to form a nucleus in the presence of high salt concentrations. In the present studies, we examined the initial aggregation process of lysozyme (initial crystallization process of lysozyme) in D2O/H2O with sodium ions or potassium ions, and investigated the relationship between the surface hydrophobicity and the aggregation rate of lysozyme. The effect of sodium ions or potassium ions on the initial aggregation process of lysozyme in D2O was clearly different from H2O. The initial aggregation rate of lysozyme in H2O was slower than in D2O. In the case of H2O, the initial aggregation rate was about the same in both ions. But in the case of D2O, the initial aggregation rate was affected by the ion species and the value was lower in potassium ions than in sodium ions. These results suggest that the interaction between lysozyme molecules is stronger in D2O than in H2O. Furthermore, sodium ions have a stronger effect on the interaction than potassium ions in the case of D2O. There was a good correlation among the initial aggregation rate, surface hydrophobicity, and zeta-potential of lysozyme. The hydrophobic interaction may be an important active force in the initial aggregation process of lysozyme.