GLUTAMATE-BINDING MEMBRANE-PROTEINS OF HUMAN PLATELETS

Two fractions of glutamate-binding proteins were isolated from the total membrane fraction of human platelets by solubilization in 2% sodium deoxycholate solution, followed by affinity chromatography on glutamate-agarose. According to the data of radioligand experiments, two types of binding sites, characterized by K(d1) = 1-mu-M, B(max1) = 100 pmoles per mg protein, K(d2) = 9.3-mu-M, and B(max2) = 395 pmoles per mg protein, were detected in the first fraction, the second fraction was represented by a single type of binding site (K(d) = 1-mu-M, B(max) = 110 pmoles per mg protein). According to the data of electrophoresis in the presence of SDS, the presence of proteins with molecular weights 14, 24, 56, and 155 kD was established in the first fraction, whereas 14, 46, 71, and 155 kD proteins were detected in the second Solid-phase enzyme immunoassay (ELISA) using poly- and monoclonal antibodies to mammalian brain glutamate-binding proteins established the presence of substantial immunochemical similarity between the Protein fractions isolated and human brain synaptic membrane glutamate-binding proteins.