Nicotinate Phosphoribosyltransferase Domain Containing Protein 1 (NAPRT1)

Nicotinic acid (NA; niacin) is converted by nicotinic acid phosphoribosyltransferase (NAPRT; EC 2.4.2.11) to NA mononucleotide (NaMN), which is then converted to NA adenine dinucleotide (NaAD), and finally to nicotinamide adenine dinucleotide (NAD), which serves as a coenzyme in cellular redox reactions and is an essential component of a variety of processes in cellular metabolism including response to stress. NAPRT encodes a deduced 538-amino acid protein that is highly conserved. Transfection experiments with recombinant NAPRT in HepG2 cells, which normally lack NAPRT activity, localized the protein in the cytosol at the expected enzymatic activity. Northern blot analysis of mouse tissues showed that NAPRT mRNA is expressed at highest levels in the small intestine, liver, and kidney.