Photolabile Precursors of Glutamate: Synthesis, Photochemical Properties, and Activation of Glutamate Receptors on a Microsecond Time Scale

• Published in: Proceedings of the National Academy of Sciences - PNAS 1994-09, Vol.91 (19), p.8752-8756
• Main Authors: Wieboldt, Raymond, Gee, Kyle R., Niu, Li, Ramesh, Doraiswamy, Carpenter, Barry K., Hess, George P.
• Format: Article
• Language: English
• Subjects: Acetates; Amines; Animals; Biochemistry; Chromatography; Esters; Glutamate receptors; Glutamates - chemical synthesis; Glutamates - chemistry; Hippocampus - physiology; In Vitro Techniques; Neurons; Phosphates; Photochemistry; Photolysis; Prodrugs; Rats; Receptors; Receptors, Glutamate - metabolism; Time Factors
• ISSN: 0027-8424; 1091-6490
• DOI: 10.1073/pnas.91.19.8752

Newly synthesized photolabile derivatives of glutamate, caged glutamate, that release free glutamate on a microsecond time scale after a pulse of UV laser light are described. 2-Nitrobenzyl derivatives were attached to the amino or carboxyl groups of glutamate. Substitution with a -CO- 2group at the benzylic carbon accelerates the photolysis reaction when compared to -H and -CH3substituents. γ-O-(α-Carboxy-2-nitrobenzyl)glutamate is stable at neutral pH. In 100 mM phosphate buffer at pH 7.0, the compound is photolyzed at 308 nm with a quantum product yield of 0.14. The half-life of the major component of the photolytic reaction, as judged by the transient absorbance change at 430 nm, is 21 μ s (≈90%); the half-life of a minor component (≈10%) is 0.2 ms. The amine-linked derivatives have half-lives in the millisecond region and a 4-fold lower quantum yield. The potential of the newly synthesized compound for use in rapid chemical kinetic investigations of glutamate receptors is demonstrated. (i) The caged glutamate at 1 mM concentration does not desensitize glutamate receptors in rat hippocampal neurons. (ii) Caged glutamate (1 mM) does not inhibit activation of the receptors by 50 μ M glutamate. (iii) Photolysis of the compound induces rapid onset of transmembrane currents in rat hippocampal neurons.