title: Histidine modification with diethyl pyrocarbonate shows heterogeneity of benzodiazepine receptors.
abstract: The effect of diethyl pyrocarbonate modification of histidine on the specific binding of [3H]diazepam and its enhancement with muscimol and (+/-)-pentobarbital was investigated. Diethyl pyrocarbonate treatment produced a dose-related inhibition of specific [3H]diazepam binding to rat brain membranes with a maximal inhibition of approximately 40% at 1 mM. Scatchard analysis of the binding data showed that diethyl pyrocarbonate, while having no effect on the affinity (Kd), decreased the binding capacity (Bmax) of diazepam from a control value of 1543 +/- 116 fmol/mg of protein to 789 +/- 79 fmol/mg of protein (mean +/- SD; P less than 0.005; n = 4). Under conditions in which approximately 40% of the diazepam binding sites were modified by diethyl pyrocarbonate treatment, the ability of muscimol and pentobarbital to enhance diazepam binding was not altered. These results suggest that a histidine residue is critical for a part (approximately 40%) of the benzodiazepine binding sites and that there may exist a heterogeneity of benzodiazepine binding sites. Furthermore, these results indicate that perhaps only a portion of the benzodiazepine binding sites are functionally coupled to the gamma-aminobutyric acid receptor-ionophore complex.
mesh_terms: D000818:Animals; D001569:Benzodiazepines / Q000378:metabolism*; D001921:Brain; D055598:Chemical Phenomena; D002621:Chemistry; D003975:Diazepam / Q000378:metabolism; D004047:Diethyl Pyrocarbonate / Q000494:pharmacology*; D005561:Formates / Q000494:pharmacology*; D006639:Histidine; D008297:Male; D009118:Muscimol / Q000494:pharmacology; D010424:Pentobarbital / Q000494:pharmacology; D051381:Rats; D011955:Receptors, Drug / Q000187:drug effects*; D011963:Receptors, GABA-A; D017981:Receptors, Neurotransmitter / Q000187:drug effects*
chemical_list: D005561:Formates; D011955:Receptors, Drug; D011963:Receptors, GABA-A; D017981:Receptors, Neurotransmitter; D001569:Benzodiazepines; D009118:Muscimol; D006639:Histidine; D010424:Pentobarbital; D004047:Diethyl Pyrocarbonate; D003975:Diazepam