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
