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. Author manuscript; available in PMC: 2010 Oct 1.
Published in final edited form as: Biochim Biophys Acta. 2009 Mar 13;1790(10):997–1004. doi: 10.1016/j.bbagen.2009.03.005

Figure 3.

Figure 3

NAD biosynthetic pathways from nicotinamde and nicotinic acid in yeast, invertebrates, and mammals. (A) The NAD biosynthetic pathways in the budding yeast Saccharomyces cerevisiae and invertebrates, such as C. elegans and Drosophila. Steps from nicotinamide to NAD are shown with grey arrows. Pnc1, Npt1, Nma1 and Nma2, and Qns1 are nicotinamidase, nicotinic acid phosphoribosyltransferase, nicotinic acid mononucleotide adenylyltransferase 1 and 2, and NAD synthetase, respectively. Only Sir2 is shown as a representative NAD-dependent protein deacetylase. NaMN, nicotinic acid mononucleotide. (B) The NAD biosynthetic pathways in mammals. The de novo pathway from tryptophan and the NAD biosynthetic pathway from nicotinic acid are evolutionarily conserved, while the NAD biosynthetic pathway from nicotinamide (grey arrows) is vertebrate-specific and mediated by Nampt and Nmnat. Nicotinamide is the main precursor for NAD biosynthesis in mammals. While multiple enzymes break NAD into nicotinamide and ADP-ribose, only Sirt1 is shown here. NMN, nicotinamide mononucleotide.