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

Experimental data at 25 degrees C are reported for osmotic pressures of aqu eous solutions containing lysozyme and any one of the following salts: ammo nium sulfate, ammonium oxalate, and ammonium phosphate at ionic strength 1 or 3 M. Data were obtained using a Wescor colloid membrane osmometer at lys ozyme concentrations from about 4 to 20 g/l at pH 4, 7, or 8. Osmotic secon d virial coefficients for lysozyme were calculated from the osmotic-pressur e data. All coefficients were negative, increasing in magnitude with ionic strength. Results are insensitive to the nature of the anion, but rise slig htly in magnitude as the size of the anion increases. (C) 2000 Elsevier Sci ence B.V. All rights reserved.