Photoaffinity labeling of functional states of the nicotinic acetylcholine receptor.

The nicotinic acetylcholine receptor was subjected to photoaffinity labeling in different conformational and functional states. The photolabel used was the ion-channel blocker [3H]-TPMP+. A procedure is described for isolating labeled delta-polypeptide chains from the receptor complex by preparative SDS-polyacrylamide gel electrophoresis. The photolabel was localized in the primary structure of the delta-chain. The site of labeling was found to be identical when photoaffinity labeling was performed in the resting, desensitized, or antagonist state, respectively.