Solubilization of quisqualate-sensitive L-[3H]glutamate binding sites from guinea pig brain membranes using a...

L-[3H]Glutamate binding sites were solubilized with a zwitterionic detergent 3-[(3-cholamidopropyl)-dimethylammonio]-1-propane-sulfonate (CHAPS) plus ammonium thiocyanate from guinea pig synaptosomal membranes. The binding of L-[3H]glutamate to the solubilized binding sites was saturable and reversible. Scatchard analysis suggested the existence of two different classes of binding sites with KDs of 63.8 and 644 nM. The L-[3H]glutamate binding was displaced by excitatory amino acids with such an order of potency that L-glutamate much greater than D-glutamate congruent to L-aspartate greater than D-aspartate. Quisqualate effectively displaced the glutamate binding in biphasic manner. L-Glutamic acid diethyl ester, the quisqualate receptor antagonist, also showed a moderate displacing ability. Other neuroactive amino acid analogues displaced the glutamate binding only weakly, except for L- and D-homocysteic acids which had moderate potency. It is very likely from these results that the glutamate binding sites solubilized in this study are relevant to the physiological glutamate receptors especially of quisqualate-type.