A paralytic peptide, ψ-conotoxin Piiie has been purified and characterized from Conus purpurascens venom. Electrophysiological studies indicate that the peptide inhibits the nicotinic acetylcholine receptor (nAChR). However, the peptide does not block the binding of α-bungarotoxin, a competitive nAChR antagonist. Thus, ψ-conotoxin Piiie appears to inhibit the receptor at a site other than the acetylcholine-binding site. As ascertained by…