A natural processing product of rat diazepam binding inhibitor, triakontatetraneuropeptide (diazepam binding inhibitor 17-50) contains an alpha-helix, which allows discrimination between benzodiazepine binding site subtypes.

Synthetic peptides related to triakontatetraneuropeptide (TTN) [17TQPTDEEMLFIYSHFKQATVGDVNTDRPGLLDLK50; diazepam binding inhibitor (DBI) 17-50], a natural brain processing product of rat DBI, were analyzed for their physicochemical and ligand-receptor interaction characteristics. The ability of TTN and TTN-related fragments to displace [3H]flumazenil (ethyl-8-fluoro-5,6-dihydro-5-methyl-6-oxo-4H-imidazol[1,5a] [1,4]-benzodiazepine-3-carboxylate) or [3H]Ro 5-4864 [7-chloro-1,3-dihydro-1-methyl-5-(p-chlorophenyl)-2H-1, 4-benzodiazepine-2-one] from their respective benzodiazepine (BZ) binding site subtypes was tested in intact cerebellar culture neurons or in homogenates of cultured astrocytes. These studies indicate that the C-terminal region of TTN, which is also present in DBI 22-50, eicosapentaneuropeptide (DBI 26-50), and octadecaneuropeptide (ODN) (DBI 33-50), but not in DBI 19-41, is essential for interaction with the BZ recognition sites.