Elsevier Inc. NAD consuming enzymes nicotinamide adenine dinucleotide utilization pathway nicotinamide ---> nicotinamide mononucleotide nicotinamide riboside ---> nicotinamide mononucleotide nicotinic acid ---> nicotinic acid mononucleotide quinolinic acid ---> nicotinic acid mononucleotide Nmnat1 Nmnat2 Nmnat3 Nmrk2 Nampt Nmrk1 Nadsyn1 Qprt Naprt1 diet nicotinamide mononucleotide ---> NAD+ nicotinic acid mononucleotide ---> nicotinic acid adenine dinucleotide NAD+ ---> nicotinamide nicotinamide ---| Sirtuins quinolinic acid nicotinic acid nicotinamide riboside nicotinamide nicotinamide mononucleotide nicotinic acid mononucleotide NAD+ nicotinic acid adenine dinucleotide kynurenine metabolic pathway Sirtuins PARPs nicotinic acid adenine dinucleotide ---> NAD+ diet ---> nicotinic acid kynurenine metabolic pathway ---> quinolinic acid diet ---> nicotinamide riboside