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Identification of a Cl − /Ca 2+ ‐Dependent Glutamate (Quisqualate) Binding Site in Bovine Pineal Organ
Author(s) -
Govitrapong Piyarat,
Ebadi Manuchair,
Murrin L. Charles
Publication year - 1986
Publication title -
journal of pineal research
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.881
H-Index - 131
eISSN - 1600-079X
pISSN - 0742-3098
DOI - 10.1111/j.1600-079x.1986.tb00745.x
Subject(s) - glutamate receptor , glutamic acid , kainate receptor , kainic acid , binding site , chemistry , biology , biochemistry , quisqualic acid , nmda receptor , amino acid , stereochemistry , receptor , ampa receptor
The presence of a high concentration of glutamic acid, a transmitter shown to have excitatory action in the pineal organ, prompted us to search for and to characterize glutamate receptor site in the bovine pineal organ. By using 10 nM‐100 μM of labeled and unlabeled L‐glutamate and by employing the LIGAND computer program, we found a glutamate binding site with a dissociation equilibrium constant (KD) of 0.534 μM and a receptor density (Bmax) of 4.84 pmol/mg protein. This pH‐ and temperature‐dependent binding site showed stereospecificity, was activated by Ca 2+ , and displayed affinity for both glutamate agonists and antagonists. The IC 50 values for L‐glutamate, L‐asparate, L‐cysteate, L‐cysteine sulfinate, quisqualate, and (±) ibotenate were 0.5, 2, 12, 16, 25, and 30 μM, respectively, whereas those for D‐aspartate, L‐α‐aminoadipate, L‐homocysteate, and DL(±) 2‐amino‐4‐phosphonobutyrate were greater than 100 μM. Kainate, N‐methyl‐D‐aspartate, and L‐glutamic acid diethyl ester were inactive. Based on these results, the presence of a quisqualate‐type, Cl − /Ca 2+ ‐dependent glutamate binding site in the pineal organ is suggested, and a possible neuroexcitatory role for glutamic acid, aspartic acid, and certain sulfur‐containing amino acids is also implied. The precise nature of this excitatory effect in modulating the function(s) of the pineal organ and the synthesis of its hormone(s) remains to be be elucidated.