Osmotic pressures of aqueous bovine serum albumin solutions at high ionic strength

Using osmometers similar to those described by Vilker et al. [V.L. Vilker, C.K. Colton, K.A. Smith, J. Colloid and Interface Sci. 79 (1981) 548-566] a nd Amos et al. [D.A. Amos, C.J. Radke, S. Lynn, J. Phys. Chem. B 102 (1998) 2739-2753], osmotic pressures of aqueous bovine serum albumin (BSA) soluti ons were measured at three pH (4.5, 5.4, 7.4) and at different sodium chlor ide concentrations (from 1 to 5 M). Experimental data were compared with re sults calculated from two van der Waals-type models using a potential of me an force including hard-sphere and double-layer repulsions, and van der Waa ls attraction. In both models, the Carnahan-Starling equation of state repr esents the contribution of the hard-sphere repulsion to the osmotic pressur e. Van der Waals attraction and double-layer repulsion are represented by t heir contributions to the osmotic second virial coefficient in the first mo del, or in the second, to the random-phase-approximation (RPA). Although bo th models give a semi-quantitative description of the osmotic pressures of BSA solutions at various conditions, the first model represents the data sl ightly better than the second, using the same number of adjustable paramete rs. Further improvement of modeling requires a more accurate potential of m ean force for protein molecules in salt solution. (C) 1999 Elsevier Science B.V. All rights reserved.