Localization of azidophencyclidine-binding site on the nicotinic acetylcholine receptor α-subunit

Nicotinic acetylcholine receptors in receptor-rich membranes from Torpedo californica and from T. marmorata electric tissue were photolabeled with the non-competitive inhibitor [³H]azidophencyclidine. The receptor subunits were separated on SDS-polyacrylamide gels and the α-subunits recovered from the gel, were subjected to Staphylococcus aureus V8 protease cleavage. The proteolytic fragments were resolved by SDS-polyacrylamide gel electrophoresis and were identified on protein blots by ¹²⁵I-labeled α-bungarotoxin binding and by staining with concanavalin A. The site of specific azidophencyclidine labeling has been localized to the V8-18 kDa fragment which binds toxin. Labeling of the V8-18 kDa fragment was observed in the absence and in the presence of carbamylcholine. This was found for both the species of Torpedo used here.