Conference paper

Structure and Function of the Acetylcholine Receptor

Mohyee E. Eldefrawi ; Section of Neurobiology and Behavior, Cornen University, Ithaca, N. Y., U.S.A.
Amira T. Eldefrawi ; Section of Neurobiology and Behavior, Cornen University, Ithaca, N. Y., U.S.A.

Abstract

The acetylcholine-(ACh-)receptor of electric organs of three
Torpedo species (marmorata, ocenata and caLifornica) is purified by
affinity chromatography. It acts as a single molecular species as
judged by electrophoresis, isoelectrofocusing, gel filtration and immunodiffusion
tests. It binds 10 nmoles of ACh or a-bungarotoxin
per mg protein. Its amino acids are analyzed and only = 180/o of
the cysteic acid residues occur as free SH groups. When the receptor
is analyzed for the presence of cations by atomic absorption, 4.7°/o
of its weight is found to be due to bound Ca*. When Ca++-free
solutions are used for purification, bound Ca* still contributes
0.6°/o of its weight. The receptor is an oligomer of an apparent
molecular weight of 330 000, with a high tendency to aggregate in
the absence of added detergent. It has a doughnut-like appearance
with an electron dense core, and consists of 5-6 subunits. Whereas
binding of ACh to fresh Torpedo membranes has a Kd of 2 X 10-s JI/I
and exhibits positive cooperativity, that to the purified ACh-
receptor has similar characteristics, and in addition, has a low
affinity component (Kd = 2 X 10-6 M). Antibodies, formed against
the ACh-receptor in immunized rabbits or rats, react with the
animal's own skeletal neuromuscular ACh-receptors. Incorporation
of the ACh-receptor, after mild treatment with trypsin, into oxidized
cholesterol bilayers, consistently causes increases in monovalent
cation selective conductances (10-over 100 fold), that are triggered
by ACh and carbamylcholine and inhibited by curare. The data
suggest that the ion conducting carriers or channels of the postjunctional membrane are part of the isolated receptor protein.

Keywords

Hrčak ID:

196627

URI

https://hrcak.srce.hr/196627

Publication date:

3.12.1975.

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