Nicotinamide mononucleotide adenylyltransferase (NMNAT) is the central enzyme of the NAD biosynthetic pathway. The conversion of NMN to NAD+ is catalyzed by three enzyme isoforms—namely, NMN adenyltransferases (NMNATs) that are differentially localized (NMNAT1, nucleus; NMNAT2, Golgi, cytosol-facing; NMNAT3, mitochondria)[2].