Multiple sites of action for noncompetitive blockers on acetylcholine receptor rich membrane fragments from Torpedo marmorata

The noncompetitive blocker [3H]chlorpromazine labels segment M2 but not segment M 1 of the nicotinic acetylcholine receptor α‐subunit

“…The degree of symmetry of the AChR molecule inferred from morphological and primary structure data, can thus be experimentally tested at this level. Furthermore, electrophysiological (review in [27][28][29]) as well as biochemical (review in [6,30]) evidence supports the view that the high-affinity NCB site is located within the ion channel. Photoactivatable NCBs are thus useful tools for direct identification of potential channel-forming elements within each of the AChR subunits [1,2,12,13].…”

“…A few degradations were carried out with an Applied Biosystems 470A sequencer, with on-line PTH-amino acid analysis in the 120A analyzer using the standard programs provided by the supplier. [6]. In the presence of 200/zM phencyclidine, a specific ligand for the high-affinity NCB-binding site, the incorporation of [3H]CPZ into all receptor chains was decreased.…”

Interaction of modified neurotoxins fromNaja nigricollis with the nicotinic acetylcholine receptor fromTorpedo marmorata A Raman spectroscopy study

“…The postsynaptie membranes were washed, concentrated by centrifugation and were used immediately after preparation. The concentration of toxin binding sites of the receptor was measured with tritiated toxin ~ as described by [22]. The protein concentration was typically 10-20 mg/ml, and the specific activity 2.5-3.0/amol of toxin sites/g of protein (0.4--0.5 g of active receptor/g protein).…”

Photoaffinity labeling of acetylcholine receptor in millisecond time scale

“…In addition to these effector sites binding sites for non-competitive blockers (NCBs) have been characterized primarily by binding studies with reversible ligands [3,4]. NCBs are especially interesting compounds because there is evidence that they exert their blocking effect at least partly by direct interaction with the ion channel of the AChR [5,6]. At present there is no clear evidence as to the structural correlate of this functional subunit, the ion channel of the AChR.…”

“…The AChR from Torpedo electric tissue has been shown to consist of 5 polypeptide chains (stoichiometry: LYZ, fi, y, S [7]) and a quaternary structure model has been proposed [8]. Several components of the protein complex have been implicated at times in the ion translocation process; recently, evidence was presented that the central cavity surrounded by the 5 polypeptide chains may comprise the ion channel [6] and the 6 chain was postulated to contain the NCB binding site or at least part of it [9].…”