Isolation and characterization of a putative endogenous benzodiazepineoid (endozepine) from bovine and human brain

A protein termed endozepine (EP) which inhibits the binding of benzodiazepines to synaptosomal membranes (Ki approximately 5 microM) has been purified to electrophoretic homogeneity from bovine and human brain using acidic ethanol/chloroform extraction, Bio-Sil TSK-250 gel permeation chromatography, and reverse-phase high performance liquid chromatographies. Bovine and human EP are single-chain polypeptides and have molecular weights of approximately 10,000. Both proteins are very hydrophilic and contain an abundance of lysine, glutamic, and aspartic residues. Antisera prepared against bovine EP have been used to develop a sensitive radioimmunoassay for the detection of EP in tissue and body fluids. EP immunoreactivity is widely distributed in mammalian tissues, body fluids, and various cell lines. Substantial variation in the concentrations of EP is observed in different regions of the brain.