On protein partitioning in two-phase aqueous polymer systems.

The partitioning of proteins between the coexisting phases of two-phase aqueous polymer systems reflects an intricate and delicate balance of interactions between proteins, polymers, salts and water. Experimental investigations have suggested that a large number of factors influence protein partitioning, including the types of polymers, their molecular weight and concentration; the protein sizes, conformation and composition; salt type and concentration, and solution pH; and the presence of ligands attached to the polymer which may interact with surface sites of the protein. Complementary modelling attempts have been successful in illuminating several molecular-level mechanisms influencing protein partitioning using lattice-model techniques, viral expansions and a scaling-thermodynamic approach. In spite of these experimental and modelling approaches, many of the physical phenomena associated with these complex systems are not well understood. Notably, the precise nature of the protein-polymer interactions and the potent effect of inorganic salts on the partitioning of proteins in these systems remains poorly understood.