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. Author manuscript; available in PMC: 2021 Aug 1.
Published in final edited form as: Curr Opin Neurobiol. 2020 Apr 17;63:59–66. doi: 10.1016/j.conb.2020.02.012

Fig. 3.

Fig. 3.

The NAD+ metabolic pathway. In the axon, NMN is turned into NAD+ by NMNAT2. When activated, SARM1 degrades NAD+ into nicotinamide (Nam) and ADPR or cyclic ADPR (cADPR). NMN may activate SARM1 (indicated by dashed line). Nam can be converted back to NMN by NAMPT. Another source of NMN is NR phosphorylated by NRK. The bacterial enzyme NMN deamidase can convert NMN to its deamidated counterpart, nicotinic acid mononucleotide (NaMN). Nicotinic acid riboside (NaR) and nicotinic acid (Na) can be alternate sources of NaMN (via NRK or NAPRT, respectively). NaMN can be also be made into NAD+ via conversion to NaAD by NMNAT2 and then by NADsyn into NAD+.