An immunochemical approach to the identification of the MBTA binding site of the nicotinic acetylcholine receptor of Torpedo californica.

Monospecific anti-[4-(N-maleimidobenzyl) trimethylammonium] (MBTA) antibodies were prepared from sera of rabbits immunized with an albumin-MBTA conjugate and used to synthesize an MBTA-specific immunosorbent. Torpedo californica acetylcholine receptor was affinity labeled with [3H]-MBTA and proteolyzed extensively with pronase, and the peptide fraction of the digest chromatographed on the anti-MBTA resin. The amino acid composition of the purified MBTA-peptide fraction was compared with the sequences flanking the seven cysteinyl residues of the alpha-subunit. The best fit was observed with the segment containing cysteine 142.