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Published September 1, 1981 | public
Journal Article Open

In vitro synthesis, glycosylation, and membrane insertion of the four subunits of Torpedo acetylcholine receptor


We have characterized the early biosynthetic forms of the Torpedo electroplax acetylcholine receptor by using a cell-free protein synthesizing system. We obtained primary translation products of ≈38, 50, 49, and 60 kilodaltons for the α, ß, γ, and δ polypeptides, respectively, by using immunoprecipitation with subunit-specific antisera. These chains could each be labeled by the formylated initiator [35S]Met-tRNA. On cotranslational incubation with pancreatic rough microsomes, glycosylated forms of each subunit were obtained that had molecular weights close to those of their mature authentic counterparts. Extensive trypsinization reduced the glycosylated forms of the receptor subunits to glycosylated membrane-protected fragments of ≈35(α), 37(ß), 45(γ), and 44(δ) kilodaltons. In this system, then, each receptor chain spans the membrane at least once. This in vitro-synthesized material apparently exhibited neither oligomeric assembly nor -bungarotoxin binding.

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© 1981 by the National Academy of Sciences. Communicated by Jerard Hurwitz, April 20, 1981. D.J.A. is supported in part by a National Science Foundation Predoctoral Fellowship. The publication costs of this article were defrayed in part by page charge payment. This article must therefore be hereby marked "advertisement" in accordance with 18 U. S. C. §1734 solely to indicate this fact.


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