[³H]2-amino-4-phosphonobutyric acid was synthesized by the conjugate addition of 1-lithio-2-trimethylsilyethyne to diethyl ethynylphosphate followed by catalytic tritiation and hydrolysis. Radiolabelled 2-amino-4-phosphonobutyric acid binds to a distinct class ofl-glutamate binding sites and does not exhibit appreciable binding to sites not displaced byl-glutamate. The binding affinity (K_d = 5.1 ± 0.4 μ M) and pharmacological profile correspond to those values obtained from physiological studies of 2-amino-4-phosphonobutyric acid inhibition of synaptic transmission, and to those values obtained in [³H]l-glutamate binding assays. [³H]2-amino-4-phosphonobutyric acid does not exhibit significant binding to the Cl⁻/Ca²⁺-independentl-glutamate binding site(s), nor to the Na⁺-dependentl-glutamate binding site (up to 50 mM Na⁺). These data provide further evidence that the physiological action of 2-amino-4-phosphonobutyric acid is mediated by the previously described Cl⁻/Ca²⁺-dependentl glutamate binding sites, and provides an assay system which is optimal for the study of these sites.

Keywords: glutamate receptors; 2-amino-4-phosphonobutyric acid; excitatory amino acids