Subunit composition of bovine muscle acetylcholine receptor

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Abstract
Acetylcholine receptors from fetal calf muscle were purified to homogeneity (specific activity up to 7500 nmol/g of protein), in reasonable yields (20-50%), and near-milligram quantity. Purification was by affinity chromatography on Naja naja siamensis toxin coupled to agarose by using methods similar to those for receptors from fish electric organs, but with modifications to account for the low concentration of receptor in muscle and the high probability of proteolysis. Immunochemical methods are described for approximating the extent of proteolysis in receptor preparations. Bovine acetylcholine receptor is composed of 4 glycoprotein subunits designated .alpha. (MW .simeq. 41,000), .beta. (MW .simeq. 50,000), .gamma. (MW .simeq. 53,000) and .delta. (MW .simeq. 56,000) which correspond immunochemically to the 4 glycoprotein subunits of fish electric organ acetylcholine receptors of the same designations. Electron micrographs of purified bovine receptor show that it has the same size and shape as receptors from fish electric organs. Immunization of rats with receptor from bovine and human muscle is very effective at inducing experimental autoimmune myasthenia gravis. Acetylcholine receptors purified from rat muscle are composed of subunits which correspond immunochemically to the .alpha., .beta., .gamma. and .delta. subunits of receptor from Torpedo californica. Acetylcholine receptors from fish electric organ tissue and mammalian muscle apparently share a fundamentally similar shape, antigenic structure and .alpha.2.beta..gamma..delta. subunit structure.

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