NADP nicotinamide adenine dinucleotide tryptophan

Nicotinic acid derivatives occur in biologic materials as the free acid, as nicotinamide, and in two coenzymatic forms nicotinamide adenine dinucleotide (NAD), and nicotinamide adenine dinucleotide phosphate (NADP). These coenzymes act in series with flavoprotein enzymes and, like them, are hydrogen acceptors or, when reduced, donors. Several plants and bacteria use a metabolic pathway for the formation of nicotinic acid that is different from the tryptophan pathway used by animals and man (B39). 

Nicotinate and nicotinamide, together referred to as niacin, are required for biosynthesis of the coenzymes nicotinamide adenine dinucleotide (NAD"") and nicotinamide adenine dinucleotide phosphate (NADP" ). These both serve in energy and nutrient metabolism as carriers of hydride ions (see pp. 32, 104). The animal organism is able to convert tryptophan into nicotinate, but only with a poor yield. Vitamin deficiency therefore only occurs when nicotinate, nicotinamide, and tryptophan are all simultaneously are lacking in the diet. It manifests in the form of skin damage (pellagra), digestive disturbances, and depression. 

Niacin is also known as vitamin PP or vitamin Bj. The term niacin describes two related compounds, nicotinic acid and nicotinamide (Figure 19.18), both with biological activity. Niacin is formed from the metabolism of tryptophan, and therefore it is not strictly a vitamin. It is a precursor of two cofactors nicotinamide adenine dinucleotide (NAD) and nicotinamide adenine dinucleotide phosphate (NADP), which are essential for the functioning of a wide range of enzymes involved in redox reactions. 

Niacin is a generic term which refers to two related chemical compounds, nicotinic acid (6.22) and its amide, nicotinamide (6.23) both are derivatives of pyridine. Nicotinic acid is synthesized chemically and can be easily converted to the amide in which form it is found in the body. Niacin is obtained from food or can be synthesized from tryptophan (60 mg of dietary tryptophan has the same metabolic effect as 1 mg niacin). Niacin forms part of two important co-enzymes, nicotinamide adenine dinucleotide (NAD) and nicotinamide adenine dinucleotide phosphate (NADP), which are co-factors for many enzymes that participate in various metabolic pathways and function in electron transport. 

Niacin, a water-soluble vitamin vital for oxidation by living cells, functions in the body as a component of two important coenzymes nicotinamide adenine dinucleotide (NAD) and nicotinamide adenine dinucleotide phosphate (NADP). NAD and NADP are involved in the release of energy from carbohydrate, fat, and protein, and in the synthesis of protein, fat, and pentoses for nucleic acid formation. Milk is a poor source of preformed niacin, containing about 0.08 mg per 100 g. However, milk s niacin value is considerably greater than indicated by its niacin content (Horwitt et al. 1981). Not only is the niacin in milk fully available, but the amino acid tryptophan in milk can be used by the body for the synthesis of niacin. For every 60 mg of tryptophan consumed, the body synthesizes 1 mg of niacin. Therefore, the niacin equivalents in 100 g milk equal 0.856 mg including that from pre-... 

It is not strictly correct to regard niacin as a vitamin. Its metabolic role is as the precursor of the nicotinamide moiety of the nicotinamide nucleotide coenzymes, nicotinamide adenine dinucleotide (NAD) and NADP, and this can also be synthesized in vivo from the essential amino acid tryptophan. At least in developed countries, average intakes of protein provide more than enough tryptophan to meet requirements for NAD synthesis without any need for preformed niacin. It is only when tryptophan metabolism is disturbed, or intake of the amino acid is inadequate, that niacin becomes a dietary essential. 

Nicotinamide-adenine dinucleotide (NAD diphosphopyri-dine nucleotide) and nicotinamide-adenine dinucleotide phosphate (NADP also termed triphosphopyridine nucleotide) represent most of the niacin activity found in good sources that include yeast, lean meats, liver, and poultry. Milk, canned salmon, and several leafy green vegetables contribute lesser amounts but are still sufficient to prevent deficiency. Additionally, some plant foodstuffs, especially cereals such as corn and wheat, contain niacin bound to various peptides and sugars in forms nutritionally not readily available (niacinogens or niacytin). Because tryptophan is a precursor of niacin, protein provides a considerable portion of niacin equivalent. As much as two thirds of niacin required by adults can be derived from tryptophan metaboHsm via nicotinic acid ribonucleotide... 

The answer is a. (Murray, pp 627-661. Scriver, pp 3897-3964. Sack, pp 121—138. Wilson, pp 287-320.) The major contributor of electrons in reductive biosynthetic reactions is nicotinamide adenine dinucleotide phosphate (NADPH -I- H ), which is derived by reduction of NAD. NAD is formed from the vitamin niacin (also called nicotinate). Niacin can be formed from tryptophan in humans. In the synthesis of NAD, niacin reacts with 5-phosphoribosyl-l-pyrophosphate to form nicotinate ribonucleotide. Then, AMP is transferred from ATP to nicotinate ribonucleotide. Finally, the amide group of glutamate is transferred to the niacin carboxyl group to form the final product, NAD. NADP is derived from NAD by phosphorylation of the 2 -hydroxyl group of the adenine ribose moiety. The reduction of NADP to NADPH -I- H occurs primarily through the hexose monophosphate shunt. 

Figure 2 NAD biosynthesis subsystem diagram. Major functional roles are shown by 4-6 letter abbreviations (explained in Table 1) over the colored background reflecting the key aspects or modules (pathways) that comprise NAD biosynthesis in various species. Catalyzed reactions are shown by solid straight arrows, and corresponding intermediate metabolites are shown as abbreviations within ovals Asp, L-aspartate lA, Iminoaspartate Qa, quinolinic acid Nm, nicotinamide Na, nicotinic acid NaMN, nicotinic acid mononucleotide NMN, nicotinamide mononucleotide RNm, N-ribosyInicotinamide NaAD, nicotinate adenine dinucleotide NAD, nicotinamide adenine dinucleotide NADP, NAD-phosphate Trp, tryptophan FKyn, N-formylkynurenine Kyn, kynurenine HKyn, 3-hydroxykynurenine HAnt, 3-hydroxyanthranilate and ACMS, a-amino-/3-carboxymuconic semialdehyde. Unspecified reactions (including spontaneous transformation and transport) are shown by dashed arrows.

Nicotinic acid and nicotinamide These are sometimes known by the generic term niacin. Their importance is in combination with tryptophan, as the coenzyme forms nicotinamide adenine dinucleotide (NAD + ) and nicotinamide adenine dinucleotide phosphate (NADP). HPLC is too insensitive to measure endogenous plasma levels, but the urinary metabolites N-methyl-2-pyridone-5-carboxylamide and N -methylnicotinamide can be measured to assess niacin status. Preliminary cleanup of urine by anion-exchange resins is followed by reversed-phase HPLC with UV detection. 

Niacin, also known as vitamin B3, nicotinic acid or vitamin PP, is a water-soluble B-complex vitamin (Table 7.1). This vitamin is the generic descriptor for two vitamers niacin and niacinamide. In the research literature the terms nicotinic acid/nicotinamide are most commonly used, while in medical practice niacin/niadnamide are preferred. The vitamin is obtained from the diet in the form of nicotinic acid, nicotinamide and tryptophan, which are transformed to nicotinamide adenine dinucleotides, NAD and NADP. These compounds participate in cellular oxidation-reduction reactions that are critical for energy production. NAD and NADP also participate in a wide variety of... 

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