Phosphorescence and optically detected magnetic resonance (ODMR) have been used to characterize two synthetic peptides, α181-198 and α185-196, of the major binding determinant of the α-acetylcholine receptor (AChR) of Torpedo californica and its interaction with α-bungarotoxin (BgTX) using Trp as an intrinsic probe. BgTX conformational changes are suggested upon complexation with the peptides. Methylmercury- modified peptides show conformational heterogeneity which brings some of the modified Cys residues into proximity of peptide Trp(s). These modified peptides, when bound to BgTX, undergo structural changes which remove the tagged Cys from its close contact with the Trp residue(s) of the peptide.
