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Published October 1, 1980 | Published
Journal Article Open

Topographic studies of Torpedo acetylcholine receptor subunits as a transmembrane complex

Abstract

The exposure of the four subunits of the acetylcholine receptor from Torpedo californica on both the extracellular and cytoplasmic faces of the postsynaptic membranes of the electroplaque cells has been investigated. Sealed membrane vesicles containing no protein components other than the receptor were isolated and were shown to have 95% of their synaptic surfaces facing the medium. The susceptibility of the four receptor subunits in these preparations to hydrolysis by trypsin both from the external and from the internal medium was used to investigate the exposure of the subunits on the synaptic and cytoplasmic surfaces of the membrane. It was shown by sodium dodecyl sulfate gel electrophoresis of the tryptic products that all four subunits are exposed on the extracellular surface to a similar degree. All four subunits are also exposed on the internal surface of the membrane, but the apparent degree of exposure varies with the subunit size, the larger subunits being more exposed. The results are discussed in terms of a possible topographic model of the receptor as a transmembrane protein complex.

Additional Information

© 1980 National Academy of Sciences. Communicated by James F. Bonner, July 11, 1980. We are grateful to Dr. Jean-Paul Revel and Wilson Wu for help with electron microscopy. We thank John Racs for expert technical assistance and Valerie Purvis for the typing and artwork. This research was supported by U.S. Public Health Service Grant NS 10294, by a grant from the Muscular Dystrophy Association of America, and by a National Institutes of Health Predoctoral Traineeship (5 T32 GM 07616-02). 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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August 22, 2023
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October 18, 2023