Similarity of Acetylcholine Receptors of Denervated, Innervated and Embryonic Chicken Muscles

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Abstract
The native (9-S) form of the acetylcholine receptor, purified from chick embryonic or adult innervated or denervated chicken muscles, was shown in each case to contain 3 subunits of MW .apprx. 40,000 (predominant), 50,000 and 54,000. The 40,000-MWr subunit (termed .alpha.) appears to exist in 2 forms; the minor variant form of it, with MW .apprx. 41000, may have a different carbohydrate content. Bromo[3H]acetylcholine, an affinity alkylating reagent for this receptor, labels the 40,000-MW subunit and the accompanying 41,000-MWr variant. The apparent ratio of the subunits varies with the several methods of detection used (protein staining, radio-iodination or tritiation) but the .alpha. subunit always predominates. The .alpha. subunit was separated in urea gel isoelectric focusing; its isoelectric point was identical there for the 3 receptors from innervated, denervated and embryonic muscles. Their respective peptide maps for the .alpha. subunit were identical, and likewise for the 54,000-MWr subunit. The subunit structures of the junctional, extrajunctional and embryonic chick muscle receptors are identical. Although the .alpha. subunit in the receptor from Torpedo electric organ, cat muscle and chicken muscles is distinguishable in all 3 cases in dodecylsulfate gel electrophoresis, it is affinity-labeled in each case. The peptide map of this subunit after limited proteolysis is also very similar in all 3 cases. The .alpha. subunits from these 3 diverse sources are closely related structurally.