Caged NADP and NAD. Synthesis and characterization of functionally distinct caged compounds.

Abstract

Two caged NADP compounds have been synthesized and characterized for use in the crystallographic study of isocitrate dehydrogenase (IDH), as well as for general use in cell biology, metabolism, and enzymology. One caged NADP compound has been designed to be "catalytically caged" so that it can bind to IDH prior to photolysis but is not catalytically active. A second NADP compound is "affinity caged" so that addition of the caging group inhibits binding of the compound to IDH prior to photolysis. The catalytically caged compound was synthesized in a two-step process, starting with the NADase-catalyzed exchange of a synthetic nicotinamide derivative onto NADP. X-ray structures of the NADP compounds with IDH show the catalytically caged NADP bound to the enzyme with its nicotinamide group improperly positioned to allow turnover, while the affinity caged NADP does not bind to the enzyme at concentrations up to 50 mM. Two analogous caged NAD compounds have also been synthesized. The NADP and NAD compounds were characterized in terms of kinetics, quantum yield, and product formation. The affinity caged NADP compound P2'-[1-(4,5-dimethoxy-2-nitrophenyl)ethyl] NADP (VIII) is photolyzed at a rate of 1.8 x 10(4) s-1 with a quantum yield of 0.19 at pH 7; the NAD analog P-[1-(4,5-dimethoxy-2-nitrophenyl)ethyl] NAD (IX) is photolyzed at at a rate of 1.7 x 10(4) s-1 with a quantum yield of 0.17.