Affinity partitioning and centrifugal counter-current distribution of membrane-bound opiate receptors using naloxone-poly(ethylene glycol).

Crude synaptic membranes isolated from calf brain cortex were subjected to an aqueous two-phase system and the partition of the various membrane constituents and activities between the phases were studied. These constituents were phosphate, cholesterol and protein. The activities measured were acetyl-cholinesterase, succinate dehydrogenase, 2',3'-cyclicnucleotide-3'-phosphohydrolase and stereospecific opiate-binding. The successful fractionation of the membranes was achieved by the use of an aqueous two-phase system in a counter-current distribution process. A ligand bound to poly(ethylene glycol) with an affinity for opiate receptors was synthesized by reacting 6-aminonaloxone with tresylpoly(ethylene glycol). The ligand-polymer was used to extract membrane-bound opiate receptors into the upper, poly(ethylene glycol)-rich phase. This use of affinity partitioning resulted in membrane fractions with a 3-4 fold higher ability to bind stereospecifically etorphine than the original preparations of synaptic membranes.