NMRK1 (nicotinamide riboside kinase 1) catalyzes the reaction of NR (N-ribosylnicotinamide) and ATP to yield NMN (beta-nicotinamide D-ribonucleotide), ADP, and H+. The enzyme is also active with GTP as a phosphate donor (not annotated here) (Bieganowsky & Brenner 2004; Sasiak & Saunders 1996; Tempel et al. 2007). The reaction is annotated with ATP(4-), the major ionized form of ATP at pH 7.2 (Stockbridge & Wolfenden 2009), as the phosphate donor. NMRK1 is a cytosolic enzyme (Nikiforov et al. 2011).