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. 2015 May 7;5:419–428. doi: 10.1016/j.fob.2015.05.002

Fig. 1.

Fig. 1

Metabolic pathway for NAD(P) biosynthesis in humans. NAD biosynthesis starting from four different sources of the pyridine ring, namely QA, Na, Nam and NamR, through four distinct ways. The de novo pathway (blue dotted line) allows NAD biosynthesis starting from QA derived from Trp and Na is processed to NAD through the Preiss–Handler pathway enzymes (green dotted line). Through a salvage pathway Nam and NamR can be transformed in NMN by NMPRTase and NamRKinase respectively. Finally, some of the cellular NAD can be converted into NADP by NAD kinase (EC 2.7.1.23). QAPRTase, quinolinic acid phosphoribosyltransferase (EC 2.4.2.19); NaPRTase, nicotinic acid phosphoribosyltransferase (EC 2.4.2.11); NMPRTase, nicotinamide phosphoribosyltransferase (EC 2.4.2.12); NamRKinase, nicotinamide riboside kinase (EC 2.7.1.22); NMNAT nicotinamide mononucleotide adenylyltransferase (EC 2.7.7.1); NADS, NAD synthetase (EC 6.3.5.1).