Hydrodynamic properties of the purified glutamate-binding protein subunit of the N-methyl-D-aspartate receptor.

The hydrodynamic properties of the previously purified glutamate-binding protein from rat synaptic membranes were determined in order to estimate the molecular size of the protein in its native state. This protein is apparently a subunit of a multisubunit complex that forms the N-methyl-D-aspartate subtype of glutamate receptor and has a molecular size of approximately 70 kDa based on electrophoretic migration under denaturing conditions. On the basis of results obtained from H2O/D2O sucrose density gradient sedimentation and gel filtration chromatography of the purified glutamate-binding protein we calculated the partial specific volume of the protein-detergent complex to be 0.766 cc3/g, the Stokes radius of the complex as 4.9 nm, the Mc of the complex as 203,000 +/- 22,000 and the Mr of the protein as 182,000 +/- 19,000. These results are indicative of stable self-association of the glutamate-binding protein and are in agreement with recent studies indicating that more than one molecule of glutamate may be required to activate the N-methyl-D-aspartate receptor-associated ion channel.