Three photoreactive derivatives of μ-conotoxin G IIIA have been prepared as photoaffinity labeling reagents for muscle-type sodium channels. The reagents competitively inhibited the binding of saxitoxin to the eel sodium channel with K i values of 11–18 nM. The introduced chromogenic phenyldiazirine group on the toxin was photolyzed efficiently, and spectroscopic properties of the reagents demonstrated that irradiation and detection can be performed in a spectral region where the absorptions due to most of biological macromolecules are negligible.
