PHOTOLABILE PRECURSORS OF GLUTAMATE - SYNTHESIS, PHOTOCHEMICAL PROPERTIES, AND ACTIVATION OF GLUTAMATE RECEPTORS ON A MICROSECOND TIME-SCALE

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 -CO2- group at the benzylic carbon accelerates the photolysis reaction when compared to -H and -CH3 substituents. gamma-O-(alpha-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 mu s (approximate to 90%); the half-life of a minor component (approximate to 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 mu M glutamate. (iii) Photolysis of the compound induces rapid onset of transmembrane currents in rat hippocampal neurons.