Osmotic Pressure Measurements of Phase-Separating Protein Solutions

Measurements of the osmotic pressure of aqueous solutions of Bovine y-crystallin and of chicken-egg-white lysozyme were made as a function of solute concentration at T=20+1 °C. The equation of state for solutions of each of these proteins, of the form fll=f(c,T), was thus traced along this isotherm for protein concentrations up to 225 mg/ml. Osmotic pressure measurements were performed using a dynamic osmometer of our own design, which eliminated the long equilibration times characteristic of static osmometry. Values for the osmotic compressibility, a/ac, of y-crystallin were determined via static light scattering. These measurements are compared to the n(c) data. The protein solutions were modeled as a gas of attracting rigid spheres. The osmotic pressure data are compared to the predictions