Affinity Partitioning Using Magnetic Two-Phase Systems

Aqueous two-phase extraction has appreciable advantages in terms of ease of scaling-up and its applicability to systems containing solids such as cell and cell debris. However, because it is not always possible to achieve an extreme partitioning of a target molecule into either phase, the introduction of an affinity ligand to the system has been examined as a means of enhancing the specificity of partitioning. Covalent binding of a ligand to a phase-constructing polymer (1 –4 ); see also Chapters 29-31, and the use of ligand-bound chromatographic supports (5 –7 ); see also Chapter 33 or a pH responsive polymer (8 ); see also Chapter 34, that partitions to the upper phase have been employed as ligand-introduction procedures. As described in Chapter 34, the method using a pH responsive polymer can realize easy recovery of the target protein as a precipitate by changing the pH after specific partitioning into upper-phase, and the ligand is also easily recovered and reused after dissociation of the target protein.