Influence of sucrose on the thermodynamic properties of the 11S globulin of Vicia faba-dextran-aqueous solvent system

A study of the influence of sucrose on the thermodynamic properties of the model (protein-polysaccharide-water) system 11S globulin-dextran-water has been carried out. A significant increase in 11S globulin solubility in aqueous medium was observed in the vicinity of the protein isoelectric point on addition of sucrose to a solution of the protein. For carrying out thermodynamic investigations of this phenomenon, the borderline conditions for complete solubility of the 11S globulin in aqueous medium were chosen, namely pH 7.0, I = 0.1 mol/dm³. The effect of sucrose on the thermodynamic parameters of the different types of pair interactions in the system ( the second virial coefficients) was estimated. It was observed that the second virial coefficient of both 11S globulin and dextran increases greatly under 50% w/v sucrose in aqueous medium. The cross second virial coefficient, characterizing interactions between protein and polysaccharide, decreases, indicating an increase in the thermodynamic compatibility of the biopolymers in this case. The conditions thermodynamically sufficient for stability of the systems with respect to diffusion were calculated on the basis of the thermodynamic parameters obtained.