CHAPTER 7: The Chemistry and Biochemistry of Niacin (B₃)

Niacin, also known as vitamin B3, nicotinic acid or vitamin PP, is a water-soluble B-complex vitamin. This vitamin is the generic descriptor for two vitamers, niacin and niacinamide, which are based on a pyridine ring bound to a carboxylic group or to a carboxamide group, respectively. The vitamin is obtained from the diet in the form of nicotinic acid, nicotinamide and tryptophan, the latter being transformed in nicotinamide adenine dinucleotides, NAD and NADP. These compounds play a central role in energy metabolism, both being involved in many cellular oxidation–reduction reactions of the metabolic processes of all life forms in which they act as a hydride ion acceptor. Besides its classical role as redox coenzyme, nicotinic acid participates in a wide variety of ADP-ribosylation reactions such as DNA repair, calcium mobilization and deacetylation. In this chapter we revise chemical and biochemical aspects of the vitamin and summarize recent advances in the understanding of the biosynthesis and signalling functions of NAD and NADP.