Gamma-aminobutyric acid-modulated benzodiazepine binding sites in bacteria.

Benzodiazepine binding sites, which were once considered to exist only in higher vertebrates, are here demonstrated in the bacteria E.coli. The bacterial [3H]diazepam binding sites are modulated by GABA; the modulation is dose dependent and is reduced at high concentrations. The most potent competitors of E.Coli [3H]diazepam binding are those that are active in displacing [3H]benzodiazepines from vertebrate peripheral benzodiazepine binding sites. These vertebrate sites are not modulated by GABA, in contrast to vertebrate neuronal benzodiazepine binding sites. The E.coli benzodiazepine binding sites therefore differ from both classes of vertebrate benzodiazepine binding sites; however the ligand spectrum and GABA-modulatory properties of the E.coli sites are similar to those found in insects. This intermediate type of receptor in lower species suggests a precursor for at least one class of vertebrate benzodiazepine binding sites may have existed.