Aqueous polymer two-phase systems and their use in fragmentation and separation of biological membranes for the purpose of mapping the membrane structure.

When solutions of two different polymers are mixed, phase separation often occurs even at low concentrations of polymers. One polymer usually collects in one phase and the other polymer in the other phase. When water is used as solvent, two aqueous, immiscible, phases are obtained. The same holds for aqueous mixtures of a salt and a polymer. Such aqueous two-phase systems (ATPS) are very useful for separation of high-molecular-weight biomolecules such as proteins and nucleic acids and also for cells, cell organelles, and membrane vesicles. The phase systems can be made highly selective and they are also mild toward biomolecules and cell particles. In this review we describe how ATPS can be used for fragmentation and separation analyses of biological membranes and how this can be used for mapping of the photosynthetic membrane, the thylakoid, of green leaves.