Biotinylated 1012-S conjugate as a probe ligand for benzodiazepine receptors: characterization of receptor binding sites and receptor assay for benzodiazepine drugs.

A nonisotopic receptor assay using the biotin-1012-S conjugate was developed and the usefulness of this conjugate as a probe ligand for the benzodiazepine receptor was evaluated. The conjugate was incubated in a receptor suspension, and then the concentration of free conjugate in the supernatant was determined nonisotopically with a solid-phase avidin-biotin binding assay. Studies on the ligand saturation with the conjugate demonstrated that the conjugate has very high affinity and specificity for the receptors and the biotin labeling does not decrease the affinity of 1012-S. This assay method was applied to the characterization of binding sites of benzodiazepine receptors in cow brain. Competition interactions between the conjugate and benzodiazepine drugs gave well-defined dose-response curves. These results confirm the possibility that this conjugate could serve as a probe for the study of receptor-ligand interactions and provide the basis of a new nonisotopic receptor assay for benzodiazepine drugs.