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. Author manuscript; available in PMC: 2011 Aug 1.
Published in final edited form as: Biochim Biophys Acta. 2009 Nov 6;1804(8):1584–1590. doi: 10.1016/j.bbapap.2009.10.024

Fig. 2.

Fig. 2

NAD biosynthesis from nicotinamide in mammals. Nicotinamide (Nic) is the main precursor for mammalian NAD biosynthesis, and nicotinamide phosphoribosyltransferase (NAMPT) catalyzes the rate-limiting step in this pathway, producing nicotinamide mononucleotide (NMN) from nicotinamide and 5′-phosphoribosyl-1-pyrophosphate (PRPP). Then, nicotinamide/nicotinic acid mononucleotide adenylyltransferase (NMNAT) completes the conversion of NMN and ATP to NAD. Other pathways from nicotinic acid, tryptophan, and nicotinamide riboside are not shown. SIRT1 and other sirtuins use NAD for their functions and produce nicotinamide and O-acetyl-ADP-ribose. Other NAD-consuming enzymes are not shown in this figure.