Compartmentalization of enzymes and distribution of products in aqueous two-phase systems

Phase separation is a common phenomenon in water solutions of polymers due to "polymer incompatibility." Polymeric aqueous two-phase systems are much used for separations in biochemistry and cell biology. When macromolecules are included in a phase system, it is often possible to obtain a one-sided distribution to one of the phases, i.e., the macromolecule is compartmentalized within one aqueous phase. This chapter describes the thermodynamic forces which govern the partitioning of molecules in aqueous two-phase systems. For a high molecular weight macromolecule, e.g., an enzyme, both enthalpic and entropic effects contribute to a one-sided partitioning. Molecules of low molecular weight will be more evenly distributed between the phases. These mechanisms are significant in biological systems and can be used for enzyme reactors in bioconversions. Enzymatic reactions can take place with enzyme and substrate compartmentalized in one of the phases. A low-molecular weight product which is evenly partitioned between the phases can be continuously removed from the enzyme-substrate compartment. These principles are described in the enzymatic conversion of cellulose in an aqueous two-phase system.