Photoaffinity Labelling of the Benzodiazepine Receptor Compromises the Recognition Site but Not Its Effector Mechanism

When subjected to ultraviolet light flunitrazepam could be irreversibly attached to brain membrane preparations such that the affinity of the benzodiazepine receptor for certain ligands, such as diazepam, becomes markedly reduced. However, the apparent affinity for diazepam is increased by the addition of gamma-aminobutyric acid and sodium chloride, to the same extent in this membrane preparation as in membranes not so pretreated. This observation suggests that photoaffinity labelling of the benzodiazepine receptor with flunitrazepam modifies the recognition characteristics of the receptor but not its effector mechanism.