Aqueous two phase extraction of proteins

Downstream processes which are based on chromatography are limited due to capacity and scale-up issues. Classical extraction processes which are known from chemical engineering could overcome this capacity problem. Moreover, it is already known that aqueous two-phase systems (ATPS) can be applied for the extraction of biomolecules. ATPS can be formed by mixing two hydrophilic components above a critical concentration. The major advantage of ATPS compared to aqueous-organic systems lies in the aqueous character of both phases which leads to an increasing biocompatibility. In this contribution the application of ATPS for the purification of proteins is shortly reviewed. Moreover, two applications of multistage extraction of ATPS for the separation of enzymes and for the purification of monoclonal antibodies are presented. For both tasks a polyethylene glycol - phosphate salt ATPS was used. As model system for enzymes, the separation of laccase of Pleurotus Sapidus from laccase of Trametes Versicolor is shown. In addition to the experimental investigation of the process, it was also modelled using an equilibrium stage model. To purify monoclonal antibodies an extraction process is exhibited which compromises an extraction part at high sodium chloride (NaCl) concentration, a back extraction step at low NaCl concentration and a washing part with nearly no NaCl. By this extraction configuration, a high purity of monoclonal antibodies was achieved.