Characterization of acetylcholine receptor subunits in developing and in denervated mammalian muscle

We have used subunit-specific antibodies to identify and to characterize partially the alpha, beta, gamma, and delta subunits of rat skeletal muscle acetylcholine receptor (AChR) on immunoblots. The alpha subunit of rat muscle is a single band of 42 kDa, whereas the beta subunit has an apparent molecular mass of 48 kDa. Both alpha and beta subunits are glycosylated and contain one or more N-linked oligosaccharide chains that are sensitive to endoglycosidase H digestion. The gamma and delta subunits, on the other hand, each appear as doublets on immunoblots, with apparent molecular masses of 52 kDa (gamma), 48 kDa (gamma') and 58 kDa (delta), 53 kDa (delta'), respectively. In each case, the two bands are structurally related and the lower band is probably the partial degradation product of the corresponding upper band. Each of the four gamma and delta polypeptides is N-glycosylated and contains both endoglycosidase H-sensitive and endoglycosidase H-resistant oligosaccharides. When the AChRs purified from embryonic, neonatal, adult, and denervated adult rat muscles were compared, no differences in the mobilities of alpha, beta, or delta subunits on sodium dodecyl sulfate gels were detected among them, either with or without endoglycosidase treatment. The gamma subunits, which were present in AChRs purified from neonatal, embryonic, or denervated rat muscles, were also identical; no gamma subunit was detected, however, in AChRs of normal adult rat muscle.