Photoaffinity labeling of peripheral-type benzodiazepine-binding sites

The use of a novel photoaffinity label for the peripheral-type benzodiazepine-binding site is described. This compound, PK 14105, has high affinity (4 nM) and selectivity for cardiac benzodiazepine-binding sites. Under ultraviolet light, PK 14105 couples covalently to an 18,000-Da membrane protein which apparently corresponds to the (or a part of the) cardiac benzodiazepine-binding site. Since covalent attachment of PK 14105 totally precludes the binding of other ligands to this binding site, it is suggested that, during ultraviolet irradiation, this compound inserts covalently into the binding domain of the peripheral-type benzodiazepine-binding site.