Solubilization of the central benzodiazepine receptor and study of its interaction with nicotinamide

It was shown that nicotinamide and NAD inhibit the specific binding of 3H]flunitrazepam to benzdiazepine receptors without causing a direct influence of gamma-aminobutyric acid (GABA) receptors. The GABA-benzdiazepine complex was separated by solubilization with 0.5% lubrol PX. The solubilized preparations contain the binding sites for 3H]flunitrazepam alone (Kd = 5.9 nm). The Kd value for the membrane-bound benzdiazepine receptor is 2.9 nM. NAD inhibited the specific binding of 3H]flunitrazepam to the solubilized membrane preparation when used at concentrations by several orders of magnitude lower than that of nicotinamide. Using gel filtration on Sepharose 6B-CL, the molecular mass of the soluble benzdiazepine receptor protein was determined.