Spherulitic growth kinetics of protein crystals

The spherulitic growth mechanism of lysozyme crystals from aqueous solutions was examined quantitatively by taking advantage of a “buffer zone” of liquid–liquid phase separation occurring in lysozyme aqueous solution. This buffer zone technique allows us to obtain constant concentrations in both liquid phases during the whole process of crystallization from solution. Under such a constant concentration (or supersaturation) condition, a constant growth rate along the radial direction of lysozyme spherulites was obtained for the spherulitic growth from solution. This evidently indicates that the growth of lysozyme spherulites is controlled by surface kinetics rather than by volume diffusion. In addition, it was found that microscopic droplets resulted from phase separation, and heterogeneous impurities normally serve as cores causing the formation of the radial pattern of spherulites.