NMRK2 (nicotinamide riboside kinase 2) catalyzes the reaction of NAR (N-ribosylnicotinate) and ATP to yield NAMN (beta-nicotinate D-ribonucleotide), ADP, and H+ (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).