Aqueous two-phase affinity partitioning of biotinylated liposomes using neutral avidin as affinity ligand

Biotinylated small unilamellar liposomes were affinity partitioned in an aqueous poly(ethylene glycol)-dextran two-phase system using avidin coupled to dextran as affinity ligand. In the absence of affinity ligand more than 90% of the liposomes partitioned in the poly(ethylene glycol)-rich top phase, whereas in its presence more than 95% partitioned in the dextran-rich bottom phase. For this redistribution to occur 10 mM and above of lithium sulphate, or other appropriate salts, had to be added to the two-phase system. Without added salt the liposomes with complexed avidin-dextran instead partitioned in the top phase. An extended mixing time for the system was required for maximum redistribution. Less than two biotin residues per liposome, coupled via a C6 spacer arm, was required to redistribute the liposomes to the bottom phase.