Optical detection of magnetic resonance (ODMR) and phosphorescence spectroscopy have been applied to synthetic peptides derived from the α-subunit of the nicotinic acetylcholine receptor of Torpeda californica and their complexes with α-cobratoxin (CBTX). TheCBTX Trp phosphorescence is strongly quenched by the proximal disulfide linkage, while the emission wavelengths and ODMR frequencies of the 18-mer αl81–198 indicate a more hydrophobic Trp environment than in the 12-mer α185–196. Binding to CBTX produces a subtle increase in the hydrophobicity of the Trp environment for the peptides, in qualitative agreement with a recently proposed binding model, in which a receptor Trp residue interacts strongly with a hydrophobic cleft of the toxin.
