THE PURIFICATION OF MEMBRANES BY AFFINITY PARTITIONING

We describe affinity partitioning as a preparative method for membrane s and membraneous structures such as organelles, cells, and viruses. B iospecific affinity partitioning is carried out in aqueous polymer two -phase systems, commonly with polyethylene glycol and dextran as phase polymers, in an environment compatible with membrane structures. Idea lly, two-phase conditions are chosen to partition the bulk of membrane material into one phase, while the affinity ligand, conjugated to the second phase polymer, will selectively pull the membranes to be isola ted into this phase. Suitable ligands include lectins, antibodies, and receptor-specific agents. Because the method has so far been used suc cessfully in rather few instances, all using high ligand receptor dens ities in target membranes, the discussion focuses on factors to be con sidered when developing affinity partitioning conditions using new lig ands.