Solubilization, Characterization, and Partial Purification of α‐Amino‐3‐Hydroxy‐5‐Methyl‐4‐Isoxazolepropionic Acid‐, Quisqualate‐, Kainate‐Sensitive l‐Glutamate Binding Sites from Porcine Brain Synaptic Junctions

L-[3H]Glutamate binding sites were solubilized from porcine brain synaptic junctions by Triton X-114 in the presence of KCl. The solubilized binding sites bound L-[3H]glutamate reversibly with KD and Bmax values of 1.48 +/- 0.18 microM and 178.2 +/- 15.9 pmol/mg of protein, respectively. These binding sites appeared to be integral membrane glycoproteins, with sugar moieties recognized by wheat germ agglutinin. A 49.3-fold purification of these binding sites was achieved by Triton X-114 solubilization, anion-exchange chromatography, and affinity chromatography using wheat germ agglutinin-Sepharose. The apparent molecular mass of the partially purified binding sites was 620 +/- 50 kDa. L-[3H]Glutamate bound to the solubilized preparation could be effectively displaced by agonists of non-N-methyl-D-aspartate (NMDA) L-glutamate receptors but not by NMDA or alpha-amino-4-phosphonobutyrate. The rank order for the competitive ligands in displacing L-[3H]glutamate was: quisqualate greater than alpha-amino-3-hydroxy-5-methyl-4-isoxazolepropionic acid greater than L-glutamate greater than kainate.