Nicotinate metabolism

Nicotinate (niacin) and nicotinamide are precursors of the coenzymes nicotinamide-adenine dinucleotide (NAD+) and nicotinamide-adenine dinucleotide phosphate (NADP+), essential cofactors in many redox reactions. The cytosolic reactions that generate NAD+ can be classified into three groups. First, in the de novo or kynurenine pathway, ACS derived from tryptophan catabolism is spontaneously converted to QUIN, which in turn is converted successively to NAMN, NAAD, and NAD+ in reactions catalyzed by QPRT, NMNAT2, and NADSYN1. These are the first four reactions listed here. Second, in the Preiss–Handler pathway, the next three reactions listed here, extracellular nicotinate (NCA), transported into the cytosol by SLC22A13 or SLC5A3, is converted to nicotinate D-ribonucleotide (NAMN), which can enter the de novo pathway to be converted to NAD+.

Summary from Reactome (R-HSA-196807), read 2026-09-23.