Countercurrent Chromatography of Proteins with Polymer Phase Systems

Abstract

Polymer phase systems were first introduced by P. Å. Albertsson in the 1950s for partitioning macromolecules and cell particles (1). These two-phase solvent systems consist of either one polymer component such as polyethylene glycol (PEG) and a high concentration of salt such as potassium phosphate, or two different polymers such as PEG and dextran in water. Being free from the organic solvent, the system can preserve a natural structure of proteins if the pH of the system is kept within a physiological range. In the past, polymer phase systems composed of PEG and potassium phosphate have been most successfully used for the protein separation. In these polymer phase systems, proteins are distributed according to their partition coefficients, which provide the basis for their purification. For example, relatively hydrophobic proteins distribute more into the PEG-rich upper phase and hydrophilic proteins into the phosphate-rich lower phase. Thus, repeating this partition process in a chromatographic column will result in separation of proteins according to their partition coefficients: the hydrophilic proteins will elute earlier than the hydrophobic proteins when the lower phase is used as the mobile phase.