Abstract: Both vapor diffusion approach and batch mode are often used approaches for protein crystallization. The light scattering method is a powerful tool particularly for prenucleation study. However, all light scattering studies were limited to the crystallization process of the batch mode. To apply dynamic light scattering technique to the protein crystallization study for the vapor diffusion approach, as well as the batch mode, a special sample cell (see Fig.1) was desired in the present work. It has two separate parts, a scattering cell and a thin tube filled with salt solution. The results showed that our special cell was reliable for light scattering study(see table 1). In our experiments, vapor diffusion approach was mainly used. Sodium acetate buffer solution, 0.04 mol•L－1, pH=4.5, was mixed with sodium chloride,whose final concentration was 0.345 mol•L－1. Chicken egg white lysozyme was dissolved in the above solution with a concentration of 50 mg•mL－1 and 25 mg•mL－1. Two lysozyme dissolution ways were used. One was lysozyme dissolved in only sodium acetate buffer solution and another is in buffer solution with sodium chloride. Their results were different(see Fig.2 and Fig.5), that showed NaCl played an important role in the interaction of lysozyme molecules. Due to the feature of vapor diffusion approach, it was verified that the force between lysozyme moleculars in the solution is weak during the whole crystallization process, which is desirable for crystal growth, namely, lysozyme molecules kept in monomolecule or aggregation of bimolecules in solution when lysozyme crystal grew. Besides, our results show that there is a significant difference between this approach and the batch mode(decreasing temperature) even if other parameters are the same. This significant difference is the direct result of different ways of supersaturation. Vapor diffusion approach, compared to batch mode is a more temperate, precisely controlled way to realize supersaturation.

Key words: Dynamic light scatter, Vapor diffusion approach, Crystal growth, Lysozyme, Diffusion coefficient, Batch method