Osmotic pressures and second virial coefficients for aqueous saline solutions of lysozyme

Experimental data at 25°C are reported for osmotic pressures of aqueous solutions containing lysozyme and any one of the following salts: ammonium sulfate, ammonium oxalate, and ammonium phosphate at ionic strength 1 or 3 M. Data were obtained using a Wescor colloid membrane osmometer at lysozyme concentrations from about 4 to 20 g/l at pH 4, 7, or 8. Osmotic second virial coefficients for lysozyme were calculated from the osmotic-pressure data. All coefficients were negative, increasing in magnitude with ionic strength. Results are insensitive to the nature of the anion, but rise slightly in magnitude as the size of the anion increases.