05-10E

A Donnan equilibrium for a series of systems is studied. In order to describe the unusually low osmotic pressure in many experiments we assumed protein molecules can form dimers. The model solution contains proteins in monomeric or dimerized forms, co- and counterions, which are modelled as charges spheres. The associative mean spherical and hypernetted chain approximations were applied to this model. In order to test the theory a Monte Carlo simulations were performed for the model mimicking lysozyme solution in 0.1M sodium chloride buffer. Using the theoretical approaches mentioned above we analyzed experimental data for the osmotic pressure of bovine serum albumin in 0.15M sodium chloride, human serum albumin solution in 0.1M phosphate buffer and lysozyme in sulphate and phosphate buffers.