Glycine and D-serine increase the affinity of N-methyl-D-aspartate sensitive glutamate binding sites in rat brain synaptic membranes

In previously frozen and extensively washed brain membranes [3H]glutamate binds to a single population of sites characteristic of the NMDA-sensitive glutamate receptor subtype. This binding cannot be displaced by glycine and D-serine, but actually is enhanced by these amino acids in a dose-dependent manner. Glycine and D-serine increase the affinity of glutamate binding without changing the density of binding sites. These results delineate glycine as an allosteric modulator of the recognition site for the NMDA-sensitive glutamate receptor.