Nucleotides, niacinamide

Nicotinamide(niacinamide) adenine dinucleotide, NAD+, and the flavin mono- and di- nucleotides (FMN, FAD) exist in oxidized and reduced forms. This makes them invaluable cofactors in enzymatically catalyzed oxidation-reduction reactions. 

Two compounds, nicotinic acid and nicotinamide, have the biological activity of niacin. When nicotinic acid was discovered to be a curative and preventive factor for pellagra, it was already known as a chemical compound, and was therefore never assigned a number among the B vitamins. The name niacin was coined in the USA when it was decided to enrich maize meal with the vitamin to prevent pellagra - it was considered that the name nicotinic acid was not desirable because of the similarity to nicotine. In USA, the term niacin is commonly used to mean specifically nicotinic acid, and nicotinamide is known as niacinamide elsewhere niacin is used as a generic descriptor for both vitamers. Figure 2.16 shows the structures of nicotinic acid, niacin and the nicotinamide nucleotide coenzymes, NAD and NADE... 

Pyridine nucleotides are intimately associated with niacin, another B vitamin (the pellagra-preventive factor). Niacin is a simple pyridine derivative, pyridine-3-carboxylic acid or nicotinic acid. The amide (niacinamide, nicotinamide) also prevents pellagra. The vitamin appears in the coenzyme in this form ... 

Preformed niacin occurs in foods either as nicotinamide (niacinamide) or as the pyridine nucleotide coenzymes derived from it, or as nicotinic acid, without the amide nitrogen, which is the form known as niacin in North America. Both nicotinamide and nicotinic acid are equally effective as the vitamin, but in large doses they exert markedly different pharmacological effects, so it is important, at least in that context, to make and maintain the distinction. In addition to the preformed vitamin, an important in vivo precursor is the amino acid L-tryptophan, obtained from dietary protein. Because the human total niacin supply, and hence niacin status, depends on the dietary tryptophan supply as well as on the amount of preformed dietary niacin and its bioavailability, it has become the accepted practice to express niacin intakes as niacin equivalents, ... 

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