Subunit structure of the acetylcholine receptor from denervated rat skeletal muscle

Acetylcholine receptor from denervated rat leg muscle was purified 48,000-fold by affinity chromatography on concanavalin A/Sepharose and cobrotoxin/Sepharose. A control preparation containing only contaminants was made by performing a parallel purification in which alpha-bungarotoxin was added to the preparation prior to the cobrotoxin/Sepharose step. Comparison of the receptor was greater than 90% pure. Examination of the purified receptor by polyacrylamide gel electrophoresis in sodium dodecyl sulfate revealed two major polypeptide chains with apparent weights of 45,000 and 51,000, along with minor components of 49,000, 56,000, 62,000, and 110,000. Polypeptides of the same molecular weight were found when purified acetylcholine receptor was radioiodinated and further purified by sucrose gradient sedimentation. Analysis of receptor purified from denervated muscles that had been incubated with [35S]methionine in organ culture showed that all of the identified polypeptide chains were radioactive, indicating that they had been synthesized de novo after denervation.