Purification of Acetylcholine-Receptor Enriched Membranes by Use of Affinity Partitioning

Membrane fragments rich in acetylcholine receptor from the electric organ of Torpedo caLifornica were purified by a combination of classical methods and affinity partitioning, a method analogous to affinity chromatography. Affinity partitioning is based upon the phase partition method where two water-rich liquid phases are formed upon the addition of sufficient quantities of water soluble polymers such as poly(ethylene oxide) and dextran. A phase system in which less than 2°/o of acetylcholinesterase, adenosine triphosphatase and a-toxin binding activities di,s,tribute ilnto the poly(ethylene oxide) rich phase was chosen. By adding cholinergic derivatives of poly(ethylene oxide), selective changes in the distribution of membrane fragments rich in acetylcholine receptor into the poly(ethylene oxide) rich were achieved. Sodium dodecyl sulfate polyacrylamide gel electrophoresis as well as assay of cobra a-toxin binding, acetylcholinesterase and adenosinetriphosphatase activities indicate that substantial purification of membrane- bound acetylcholine receptor was achieved