The de novo pathway (shown in red) begins with aspartate, while the salvage pathway (shown in blue) uses either nicotinamide or nicotinate mononucleotide as its starting substrate. The reaction catalyzed by NMAT sits at the branch point between the two pathways (outlined with a box). Gene names are shown in parentheses. Abbreviations used: DHAP, dihydroxyacetone phosphate; PRPP, 5-phospho-ribose-1-pyrophosphate; NaMN, nicotinate mononucleotide; NaAD, nicotinate adenine dinucleotide; NAD, nicotinamide adenine dinucleotide; NADP, nicotinamide adenine dinucleotide phosphate.