[3H]AHN 086 acylates peripheral benzodiazepine receptors in the rat pineal gland

Abstract

AHN 086, an isothiocyanato derivative of Ro 5-4864 (4′-chlorodiazepam), inhibits radioligand binding to peripheral benzodiazepine receptors with characteristics of an irreversible (acylating) ligand. We now report that [³H]AHN 086 labels a ≈ 30 kDa protein in the rat pineal gland determined by both SDS-polyacrylamide gel electrophoresis and gel filtration high-performance liquid chromatography of digitonin-solubilized membranes. Specific incorporation of [³H]AHN 086 into this protein was inhibited by preincubating membranes with excess AHN 086. Moreover, significant specific binding of [³H]AHN 086 was not observed in either bovine pineal gland (which does not possess high-affinity binding sites for Ro 5-4864) or ovalbumin. These findings suggest that the ≈ kDa protein labeled by [³H]AHN 086 in rat pineal gland is associated with peripheral benzodiazepine receptors in this tissue.