Thermodynamic compatibility of proteins in aqueous media. Part. I. Phase diagrams of some water--protein A--protein B systems.

The thermodynamic compatibility of proteins belonging to different classes according to Osborne has been investigated in aqueous media. Phase equilibrium for water--ovalbumin--soybean globulin fraction, water--ovalbumin--casein, water--casein--gliadin and water--casein--soybean globulin fraction systems has been investigated. The data obtained were analysed according to the theoretical concepts of Scott, Patterson and Prausnitz concerning the effect of polymer molar masses and the solvent quality on the phase equilibrium in similar systems. The analysis performed indicates that these concepts can be applied to the water--protein A--protein B systems. The phase equilibrium in water--protein A--protein B systems has some distinctive features as compared to that in systems containing two synthetic polymers in the single solvent. Firstly, proteins are usually compatible in a broader concentration range as compared to common polymers. Moreover, the separation of water--protein A--protein B systems into two phases often results in a considerable concentration of one of the protein components. Apparently, the latter fact can be associated with the marked difference in the interaction parameter of proteins belonging to different classes with the solvent, and, hence, with the marked difference in the hydrophilicity of the proteins investigated.