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Purification and Molecular Characterization of the Brain Synaptic Membrane Glutamate‐Binding Protein
Author(s) -
Michaelis Elias K.,
Michaelis Mary L.,
Stormann Thomas M.,
Chittenden W. Leroy,
Grubbs Robert D.
Publication year - 1983
Publication title -
journal of neurochemistry
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.75
H-Index - 229
eISSN - 1471-4159
pISSN - 0022-3042
DOI - 10.1111/j.1471-4159.1983.tb08150.x
Subject(s) - glutamate receptor , amino acid , biochemistry , isoelectric point , glutamic acid , binding protein , membrane , chemistry , cysteine , biophysics , biology , receptor , enzyme , gene
A glutamate‐binding protein from rat brain synaptic plasma membranes has been purified to apparent homogeneity. This protein has a M r of 14,300 based on amino acid and carbohydrate analyses. The protein is enriched with tryptophan residues, which contribute substantially to its hydrophobic nature. It also has a relatively high content of acidic amino acids, which determine its low isoelectric point (4.82). The protein exhibits either a single, high‐affinity class of sites for L‐[ 3 H]glutamate binding (K D = 0.13 μM) when binding is measured at low protein concentrations, or two classes of sites with high (K D = 0.17 μM) and low affinities (K D = 0.8 μM) when binding is measured at high protein concentrations. These observations suggest preferential binding of L‐glutamate to a self‐associating form of the protein. The displacement of protein‐bound L‐[ 3 H]glutamic acid by other neuroac‐tive amino acids has characteristics similar to those observed for displacement of L‐glutamate from membrane binding sites. Chemical modification of the cysteine and arginine residues results in an inhibition of glutamate binding activity. The possible function of this protein in the physiologic glutamate receptor complex of neuronal membranes is discussed.