Extraction of Amphiphilic Proteins Using Detergent-Based Aqueous Two-Phase Systems

Extraction systems based on nonionic surfactants have been described as an alternative to the standard polymer/polymer or polymer/salt systems. Phaseforming surfactants are, for example, the nonionic polyoxyethylene-type detergents. This kind of aqueous two-phase system (ATPS) is simply induced by a switch in the temperature; on the basis of the temperature-dependent reversible hydration/dehydration of the polar ethylene oxide headgroups. A single isotropic micellar phase separates into two isotropic phases: one of the resulting two aqueous phases, the so-called coazervate phase, is enriched in detergent, whereas the other is depleted (1 ). The detergent forms micelles in the detergent-depleted phase and is believed to exist in the form of lamellar stacks in the coazervate phase (bi. Both phases have a high water content. The temperature at which the phase separation occurs is referred to as the cloudpoint. The clouding temperature depends on the structure of the polyoxyethylated surfactant. This kind of ATPS is especially suited for the extraction of amphiphilic/hydrophobic biomolecules.