Nicotinamide/nicotinate mononucleotide adenylyltransferase of bifunctional proteins, also containing a Nudix hydrolase domain
N-terminal NMNAT (Nicotinamide/nicotinate mononucleotide adenylyltransferase) domain of a novel bifunctional enzyme endowed with NMN adenylyltransferase and Nudix hydrolase activities. This domain is highly homologous to the archeal NMN adenyltransferase that catalyzes NAD synthesis from NMN and ATP. NMNAT is an essential enzyme in the biosynthesis of NAD(+) and NADP(+). Nicotinamide-nucleotide adenylyltransferase synthesizes NAD via the salvage pathway, while nicotinate-nucleotide adenylyltransferase synthesizes the immediate precursor of NAD via the de novo pathway. The C-terminal domain of this enzyme shares homology with the archaeal ADP-ribose pyrophosphatase, a member of the 'Nudix' hydrolase family.