Determination of local refractive index for protein and virus crystals in solution by Mach-Zehnder interferometry.

To establish the importance of, and quantitatively evaluate, the macromolecular concentration gradients in the neighborhood of growing protein, virus, and nucleic acid crystals, a convenient, accurate, and nonintrusive method has been devised. This approach should prove particularly relevant in the rigorous comparison of crystals grown in a conventional laboratory setting with those grown in a microgravity environment. The method is based on precise determination of the local refractive index using Mach-Zehnder interferometry. Presented here are data for five protein and three virus systems. From data for these and other systems, optical monitoring experiments to measure local growth conditions and growth kinetics in liquid-liquid diffusion, batch, and vapor diffusion crystal growth experiments can be designed.