Determination of Protein-Protein Interactions at High Co-Solvent Concentrations Using Static and Dynamic Light Scattering.

Protein-protein interactions are commonly measured in terms of the second osmotic virial coefficient, B from static light scattering (SLS) or the interaction parameter, k from dynamic light scattering (DLS). Often these measurements are carried out at high co-solvent compositions, where correction factors are required for the light scattering analysis. For lysozyme in aqueous solutions containing the co-solvents NaCl, arginine chloride, urea, sucrose or guanidine chloride, we show that B determination requires using in the light scattering equation the refractive index increment of the protein measured at constant solvent chemical potential.