Glutamate metabotropic receptors (mGluRs) in bovine brain coated vesicles have been characterized by pharmacological and kinetic binding experiments. Saturation experiments revealed a single binding site with a K d = 607.9 ± 78.5 nM and a B max = 6.45 ± 0.88 pmol/mg protein. The specific binding of l-[3H]glutamate to mGluRs is regulated by guanine nucleotides. Guanosine-5'-triphosphate (GTP; 100 μM) shifts the agonist competition curves to the right, increasing the IC50 values. Pertussis toxin treatment produces a pharmacological binding profile for quisqualate similar to that obtained in the presence of 100μM GTP. These results indicate the presence of metabotropic glutamate receptors in coated vesicles and its coupling to a pertussis toxin sensitive G-protein.
