Dinucleotides

Coemymes effecting transfer of hydrogen. These include the pyridine nucleotides, nicotinamide-adenine dinucleolide and nicotinamide-adenine dinucleolide phosphate the flavin nucleotides such as flavin-adenine dinucleotide and lipoic acid. 

FAD Flavin-adenine dinucleotide, fahl ore, CujSbSj. Tetrahedrite. 

Packer M J, M P Dauncey and C A Hunter 2000. Sequence-dependent DNA Structure Dinucleotide Conformational Maps. Journal of Molecular Biology 295 71-83. 

In the diester method a deoxynucleoside-5 -monophosphate is condensed with the 3 -OH group of a deoxynucleotide to produce a 3, 5 -phosphodiester. This is illustrated by a general method for dinucleotide synthesis developed by H.G. Khorana (K.L. Agarwal, 1976). One N-... 

FIGURE 15 5 Structure of NAD the oxidized form of the coenzyme nicotinamide adenine dinucleotide The functional part of the coen zyme is framed in red... 

NADH is the reduced form of nicotinamide adenine dinucleotide. 

Insects poisoned with rotenone exhibit a steady decline ia oxygen consumption and the iasecticide has been shown to have a specific action ia interfering with the electron transport iavolved ia the oxidation of reduced nicotinamide adenine dinucleotide (NADH) to nicotinamide adenine dinucleotide (NAD) by cytochrome b. Poisoning, therefore, inhibits the mitochondrial oxidation of Krebs-cycle iatermediates which is catalysed by NAD. 

Glucose [50-99-7] urea [57-13-6] (qv), and cholesterol [57-88-5] (see Steroids) are the substrates most frequentiy measured, although there are many more substrates or metaboUtes that are determined in clinical laboratories using enzymes. Co-enzymes such as adenosine triphosphate [56-65-5] (ATP) and nicotinamide adenine dinucleotide [53-84-9] in its oxidized (NAD" ) or reduced (NADH) [58-68-4] form can be considered substrates. Enzymatic analysis is covered in detail elsewhere (9). 

Indicators There are certain compounds that are suitable as indicators for sensitive and specific clinical analysis. Nicotinamide adenine dinucleotide (NAD) occurs in oxidized (NAD" ) and reduced (NADH) forms. Nicotinamide adenine dinucleotide phosphate (NADP) also has two states, NADP" and NADPH. NADH has a very high uv—vis absorption at 339 nm, extinction coefficient = 6300 (M cm) , but NAD" does not. Similarly, NADPH absorbs light very strongly whereas NADP" does not. 

Fig. 2. Homeostatic control of blood Ca " level where PTH is parathyroid hormone [9002-64-6], CC, cholecalciferol, ie, vitamin D HCC, hydroxycholecalciferol DHCC, dihydroxycholecalciferol CaBP, calcium-binding protein NAD PH, protonated nicotinarnide-adenine dinucleotide...

Fig. 9. Glucuionic acid pathway. NAD = nicotinamide-adenine dinucleotide NADH = reduced nicotinamide—adenine dinucleotide ...

NADP = nicotinamide-adenine dinucleotide phosphate NADPH = reduced nicotinamide—adenine dinucleotide phosphate NDP = nucleoside... 

The biological importance of these compounds stems from their use as cofactors. Both nicotinamide and nicotinic acid ate building blocks for coen2yme I (Co I), nicotinarnide—adenine dinucleotide (NAE)) (3) and coen2yme II (Co II), nicotinarnide—adenine dinucleotide phosphate (NAE)P) (4) (2). 

The result of this biosynthesis is that the product is nicotinic acid mononucleotide rather than free nicotinic acid. Ingested nicotinic acid is converted to nicotinic acid mononucleotide which, in turn, is converted to nicotinic acid adenine dinucleotide. Nicotinic acid adenine dinucleotide is then converted to nicotinamide adenine dinucleotide. If excess nicotinic acid is ingested, it is metabolized into a series of detoxification products (Fig. 4). Physiological metabohtes include /V-methylnicotinamide (19) and A/-methyl-6-pyridone-2-carboxamide (24) (1). 

Riboflavin-5 -Adenosine Diphosphate. Riboflavin-5 -adenosine diphosphate [146-14-5] (flavin—adenine dinucleotide, FAD), C27H33N9O15P2 (2), mol wt 785.56, was first isolated in 1938 from the D-amino acid oxidase as its prosthetic group (95), where it was postulated to be... 

Although the stmctures of ribavirin and selenazofutin are similar, they appear to exert their antiviral action at different enzyme sites along the same biochemical pathway. Selenazofutin forms the nicotinamide adenosiae dinucleotide (NAD) analogue, which inhibits IMP dehydrogenase by binding ia place of the NAD cofactor, and hence this potent reduction of guanylate pools is responsible for the antiviral effect of selenazofutin. 

Coenzymes such as adenosine diphosphate (ADP), adenosine SGtriphosphate (ATP), nicotinamide adenine dinucleotide (NAD), and nicotinamide adenine dinucleotide, reduced (NADH), are involved in some reactions (4). 

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