Effective hard particle model for the osmotic pressure of highly concentrated binary protein solutions.

The experimentally measured concentration dependence of the osmotic pressure of an equimolar mixture of hen egg ovalbumin and bovine serum albumin at pH 7.0 and 25 degrees C in the presence of 0.15 M NaCl is shown to be quantitatively accounted for by a model in which each protein species is represented by an effective hard sphere. The size of this sphere is determined by analysis of the concentration dependence of the osmotic pressure of the isolated protein.