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. Author manuscript; available in PMC: 2021 Oct 1.
Published in final edited form as: Trends Biochem Sci. 2020 Jun 25;45(10):858–873. doi: 10.1016/j.tibs.2020.05.010

Figure I. Chemical Structure and Biosynthesis of NAD+.

Figure I.

(A) Chemical structure of oxidized NAD+. NAD+ comprises two nucleotides, one containing an adenine nucleobase and the other containing nicotinamide, joined through their phosphate groups. The location of various chemical moieties contained within NAD+ are indicated: ADP-ribose (ADPR), nicotinamide (NAM), nicotinamide riboside (NR), and nicotinamide mononucleotide (NMN). (B) NAD+ is synthesized de novo in a pathway leading from tryptophan (blue), as well as in ‘salvage’ pathways: (i) the nicotinic acid (NA) (‘Preiss–Handler’) salvage pathway (yellow), (ii) the nicotinamide mononucleotide (NMN) salvage pathway (green), and (iii) the nicotinamide riboside (NR) salvage pathway (green). The abbreviations for the enzymes (gray text) and the intermediates (black plain text) are defined in Table 1.