The reaction site of a non-competitive antagonist in the delta-subunit of the nicotinic acetylcholine receptor.

A site in the primary structure of the nicotinic acetylcholine receptor from Torpedo marmorata covalently labeled with the non-competitive antagonist [3H]triphenylmethylphosphonium (TPMP+) was localized. The label was found in position 262 of the delta-polypeptide chain. This site is specifically labeled in the presence of the agonist carbamoylcholine. Labeling is prevented by the non-competitive antagonist histrionicotoxin. Position 262, probably a serine, is located in the highly conserved membrane-spanning helix M2 (according to the predicted folding scheme of Finer-Moore and Stroud (1984). The relationship of this site to the receptor's ion channel and its regulation is discussed.