title: Distinct protein components from Torpedo marmorata membranes carry the acetylcholine receptor site and the binding site for local anesthetics and histrionicotoxin.
abstract: Highly purified subsynaptic membrane fragments prepared from Torpedo marmorata electric organ (specific activity, greater than 4 mumol of Naja nigricollis alpha-[3H]toxin per mg of protein) exhibit, on sodium dodecyl sulfate/polyacrylamide gel electrophoresis, two major protein bands of apparent molecular weight 40,000 and 43,000, respectively. Dissolution of these membranes by the nondenaturing detergents Triton X-100 and Berol 043 followed by standard fractionation yielded (i) the 9S acetylcholine-receptor protein which still binds the alpha-[3H]toxin and after further purification yielded, in the presence of sodium dodecyl sulfate, the 40,000-dalton component, covalently labeled by the affinity reagent 4-(N-maleimido)phenyl[3H]trimethylammonium; only serine was found as the NH2-terminal amino acid of this protein; and (ii) a high molecular weight aggregate named 43,000 protein which was resolved in denaturing gels almost exclusively as the 43,000-dalton band, In the absence of detergents, the 43,000 protein binds compounds known to interact with the acetylcholine ionophore: a fluorescent local anesthetic quinacrine and histrionicotoxin (apparent dissociation constant, 7 +/- 1 X 10(-7) M). The regulation of quinacrine fluorescennce by carbamylcholine, observed in the intact membrane, no longer occurs with the isolated 43,000 component.
mesh_terms: D000596:Amino Acids / Q000032:analysis; D000664:Amphibian Venoms / Q000378:metabolism; D000818:Animals; D001665:Binding Sites; D004546:Elapid Venoms / Q000378:metabolism; D004557:Electric Organ / Q000378:metabolism*; D005399:Fishes; D008565:Membrane Proteins / Q000378:metabolism; D008970:Molecular Weight; D009419:Nerve Tissue Proteins / Q000378:metabolism*; D010455:Peptides / Q000032:analysis; D011796:Quinacrine / Q000378:metabolism; D011950:Receptors, Cholinergic / Q000032:analysis / Q000378:metabolism*
chemical_list: D000596:Amino Acids; D000664:Amphibian Venoms; D004546:Elapid Venoms; D008565:Membrane Proteins; D009419:Nerve Tissue Proteins; D010455:Peptides; D011950:Receptors, Cholinergic; D011796:Quinacrine
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