Characterization of quisqualate-sensitive [(3)H]glutamate binding activity solubilized from rat adrenal

Pharmacological and biochemical characteristics of the binding activity of radiolabeled l-glutamic acid (Glu), a putative central excitatory neurotransmitter, were studied by using supernatant preparations solubilized from the rat adrenal by Nonidet P-40. Binding activity in the solubilized preparations was stereospecific and structure selective. This adrenal binding activity was markedly abolished by quisqualate (QA), l-glutamate diethylester and dl-2-amino-3-phosphonopropionate. None of the other agonists and antagonists for the central acidic amino acid receptors affected the binding activity. Scatchard analysis revealed that Na(+) ions significantly diminished the binding activity through decreasing the number of binding sites. A potent inhibition of the binding activity invariably resulted from the treatment of solubilized preparations with various proteases such as trypsin, chymotrypsin, papain and pronase E. Similarly significant inhibition was induced by the treatment with ?-glucosidase and phospholipase C. Heating at 70 or 100 degrees C completely abolished the binding activity, while heating at 55 degrees C induced no significant change in the activity. Cation exchange column chromatography revealed the formation of radioactive product from [(3)H]Glu during the incubation in a temperature-dependent manner. These results suggest the possible involvement of a heat-stable glycoprotein enzyme system capable of converting the central neurotransmitter to other products in the QA-sensitive [(3)H]Glu binding activity solubilized from the adrenal gland.