A Investigation of Protein Crystal Growth by Laser Light Scattering

Laser light scattering is utilized here to unobtrusively probe the submicroscopic, macromolecular events within solutions from which protein crystals grow. Lysozyme and protamine insulin were studied. In this study the formation of a precrystalline aggregate is distinguished from that of an amorphous precipitant by photon correlation spectroscopy and by classical absolute scattering intensity measurements. A slight decrease in diffusion and a slight increase in intensity are shown to mark isothermal lysozyme nucleation. Light scattering is not typically done on supersaturated solutions, so before drawing conclusions, photon correlation with multiple scattering vectors (multi-q) was used to investigate interparticle interactions within "monomeric" lysozyme solutions. The concentration and temperature dependence of the effective hydrodynamic diameter of monomeric lysozyme were determined. In the supersaturated solutions the effective hydrodynamic diameter of the quasiequilibrium state is seen to vary with the degree of supersaturation. In the monomeric solutions the influence of hydrodynamic interactions is shown to predominate that of the thermodynamic interactions. It is concluded that, although interparticle interactions affect the measurement of the effective diameter, small order aggregates are forming within the scattering volume during nucleation. Qualitative size distributions are presented, and scattering parameters for monitoring dynamically controlled lysozyme nucleation are offered.