Nicotinamide adenine dinucleotide (NAD) is the major redox co-factor in all cells. Synthesized from tryptophan or vitamin precursors, NAD is also a consumed substrate of signaling enzymes including sirtuins and poly(ADPribose) polymerase. In addition to the classically identified compounds, nicotinamide and nicotinic acid, nicotinamide riboside (NR) is an additional vitamin precursor of NAD, which was shown to be active in fungal and vertebrate systems in 2004. NR kinases (Nrk1 and Nrk2) catalyze phosphorylation of NR to produce nicotinamide mononucleotide (NMN), which is then converted to NAD by nicotinamide mononucleotide adenylyltransferases (Nmnat1, Nmnat2 and Nmnat3). Because of the key roles for NAD in metabolism, analogs of NR are being investigated as compounds that will be converted to either toxic or fluorescent compounds by virtue of Nrk and Nmnat enzyme action. In this study, we are testing the activity of Nrk1 on a series of NR analogs including 3-azidopyridine riboside, nicotinamide ethyl azide riboside, 2-deoxy bromobenzene riboside, 2-deoxy benzamide riboside, and 2-deoxy benzamide glucoside. These assays should allow us to predict which compounds can be converted to the corresponding NMN analogs in living cells. "