The nicotinic acetylcholine receptor from Torpedo marmorata was digested using papain and the reaction products separated by SDS gel electrophoresis and characterised by immunoblotting using labelled α-bungarotoxin, polyclonal antibodies to synthetic peptides and monoclonal antibodies to the main immunogenic region (MIR). Using this approach, it was possible to show that the MIR is located N-terminal to all or part of peptide 151–169 (peptide P1) of the α-chain and that papain cleaves the α-chain between Asn 141 and peptide P1.
