NMRK2 (nicotinamide riboside kinase 2) catalyzes the reaction of NR (N-ribosylnicotinamide) and ATP to yield NMN (beta-nicotinamide D-ribonucleotide), ADP, and H+ (Bieganowsky & Brenner 2004; 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. NMRK2 is a cytosolic enzyme (Nikiforov et al. 2011), localized predominantly in myocytes (Li et al. 1999).