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. 2021 Apr 24;9(4):959–972. doi: 10.1016/j.gendis.2021.04.001

Figure 1.

Fig. 1

Nicotinamide adenine dinucleotide (NAD+) biosynthetic pathways in mammals. There are two major pathways of NAD+ synthesis: the de novo pathway from tryptophan and the salvage pathway from NA, NAM and NR with different catalysing enzymes. NAD+ can also be converted to NAM by three major NAD+-consuming enzymes, SIRTs, PARPs and cADPRs. cADPRs, cyclic ADP- ribose synthases; NA, nicotinic acid; NAD+, nicotinamide adenine dinucleotide; NAM, nicotinamide; NAMN, nicotinic acid mononucleotide; NAMPT, nicotinamide phosphoribosyltransferase; NAPRT, nicotinic acid phosphoribosyltransferase; NMN, nicotinamide mononucleotide; NMNAT, nicotinamide mononucleotide adenylyltransferase; NR, nicotinamide riboside; NRK, nicotinamide ribose kinase; PARPs, poly-ADP-ribose polymerases; QAPRT, quinolinate phosphoribosyltransferase; SIRTs, sirtuin.