Mononucleotides

This past year has been highlighted by the development of novel phosphate protecting groups and their use in nucleotide and chiral nucleoside thiophos-phate chemistry. Concise methodologies have been described for cost effective syntheses of oligonucleotide building blocks. Finally, the collection of unnatural nucleotides reported to have been synthesised has been expanded significantly. 

The next DNA building units are the nucleotides, dAMP, dGMP, dCMP, and dTMP (base + deoxyribose -I- phosphate group). 

Water molecules play an important part in the behaviour of DNA and are believed to be a major factor in controlling its conformation [29]. The amount of water in the irmnediate coordination sphere is believed to be about 2OH2O per mononucleotide unit, but this is variable and depends on the cations present. Water molecules contribute to the stability of secondary and tertiary structure and they are involved in the transitions between the various crystalline forms A, B, C, D and so forth. 

The discovery of the first mononucleotide, inosinic acid, by Liebig in 1847 preceded the discovery of the nucleic acids by Miescher [17] in 1868. Inosinic acid (inosine ribose-5 -phosphale) (10.75) was isolated from beef extract, although at the time, its phosphorus content was not realised. 

The mononucleotides (mononucleoside phosphates) are obtainable by breaking down the polynucleotides or by phosphorylation of pre-formed nucleosides. Their main biochemical role is to function as sources of the nucleoside pyro- and tri-phosphates (below). 

Various isomers of the mononucleotides exist. The ribonucleosides may be phosphorylated in the 2 3 or 5 positions (10.76), whereas the deoxyribonucleosides may be phosphorylated only at 3 or 

The RNA mononucleotide unit containing adenine is adenosine-5 -monophosphate (adenylic acid) (AMP). This compound is described in Chapter 11.3 and is the hydrolysis product from adenosine triphosphate (ATP). 

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FMN See flavin mononucleotide, foamed plastics See cellular plastics. 

Bacterial concentrations have also been determined by using the enzyme-catalyzed chemiluminescent reaction of reduced flavin mononucleotide (FMN) with oxygen and aldehydes. The detection limit was reported to be 10 ceUs of E. coli, which contains 7 x 10 g of FMN per ceU (303). 

Acetylation of hydroxyl groups and esterification of carboxyl groups have been observed ia a limited number of cases but, ia geaeral, have ao preparative advantage over chemical methods. By comparison, phosphorylation has been useful ia the preparatioa of modified purine and pyrimidine mononucleotides from their corresponding nucleosides, eg, 6-thioguanosiae [85-31-4] (51) (97). 

The synthetic scheme typically involves chain-extending addition of protected mononucleotides to a nucleoside bound covalentiy at the 3 -hydroxyl to an inert siUca-based soHd support, such as controlled pore glass (Fig. 11). The initial base-protected 5 -O-dimethoxytrityl (DMT) deoxynucleoside is linked to the soHd support via the reaction of a siUca-bound amino-silane and the -nitrophenylester of the 3 -succinylated nucleoside, yielding a 3 -terminal nucleoside attached to the soHd support (1) (Fig. 11). Chain elongation requites the removal of the 5 -DMT protecting group. 

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). 

Nicotinamide is incorporated into NAD and nicotinamide is the primary ckculating form of the vitamin. NAD has two degradative routes by pyrophosphatase to form AMP and nicotinamide mononucleotide and by hydrolysis to yield nicotinamide adenosine diphosphate ribose. 

Riboflavin-5 -Phosphate. Riboflavin-5 -phosphate [146-17-8] (vitamin B2 phosphate, flavin mononucleotide, FMN, cytoflav), C2yH22N402P,... 

Flavin mononucleotide was first isolated from the yellow en2yme in yeast by Warburg and Christian in 1932 (4). The yellow en2yme was spHt into the protein and the yellow prosthetic group (coen2yme) by dialysis under acidic conditions. Flavin mononucleotide was isolated as its crystalline calcium salt and shown to be riboflavin-5Lphosphate its stmeture was confirmed by chemical synthesis by Kuhn and Rudy (94). It is commercially available as the monosodium salt dihydrate [6184-17 /, with a water solubiUty of more than 200 times that of riboflavin. It has wide appHcation in multivitamin and B-complex solutions, where it does not require the solubili2ers needed for riboflavin. 

Flavin mononucleotide (Na, 2H2O salt, FMN) [ 130-40-5JM 514.4, pKj 2.1 (PO4H2), pK2 6.5 (PO4H ), pKj 10.3 (CONH), fluorescence Xmax 530nm (870nm for reduced form). 

The first structure, flavodoxin (Figure 4.14a), has one such position, between strands 1 and 3. The connection from strand 1 goes to the right and that from strand 3 to the left. In the schematic diagram in Figure 4.14a we can see that the corresponding a helices are on opposite sides of the p sheet. The loops from these two p strands, 1 and 3, to their respective a helices form the major part of the binding cleft for the coenzyme FMN (flavin mononucleotide). 

Riboflavin, or vitamin B2, is a constituent and precursor of both riboflavin 5 -phosphate, also known as flavin mononucleotide (FMN), and flavin adenine dinucleotide (FAD). The name riboflavin is a synthesis of the names for the molecule s component parts, ribitol and flavin. The structures of riboflavin. 

As its name implies, this complex transfers a pair of electrons from NADH to coenzyme Q a small, hydrophobic, yellow compound. Another common name for this enzyme complex is NADH dehydrogenase. The complex (with an estimated mass of 850 kD) involves more than 30 polypeptide chains, one molecule of flavin mononucleotide (FMN), and as many as seven Fe-S clusters, together containing a total of 20 to 26 iron atoms (Table 21.2). By virtue of its dependence on FMN, NADH-UQ reductase is a jlavoprotein. 

Duane, W., and Hastings, J. W. (1975). Flavin mononucleotide reductase of luminous bacteria. Mol. Cell. Biochem. 6 53-64. 

Francisco, W. A., et al. (1996). Interaction of bacterial luciferase with 8-substituted flavin mononucleotide derivatives. /. Biol. Chem. 271 104-110. 

Hastings, J. W., and Gibson, Q. H. (1963). Intermediates in the bioluminescent oxidation of reduced flavin mononucleotide. J. Biol. Chem. 238 2537-2554. 

Lee, J. (1972). Bacterial bioluminescence. Quantum yields and stoichiometry of the reactants reduced flavin mononucleotide, dodecanal and oxygen, and of a product hydrogen peroxide. Biochemistry 11 3350-3359. 

Puget, K., and Michelson, A. M. (1972). Studies in bioluminescence. VII Bacterial NADH flavine mononucleotide oxidoreductase. Biochimie 54 1197-1204. 

For the anionic models, the detailed studies on their interactions with poly-and mononucleotides have not yet been carried out. However, we may say that the interactions of bases between the models and polynucleotides would be faint because of the strong electrostatic repulsive forces between the macroanions. 

Recently, Shimidzu etal.s7) studied the adsorption ability of cross-linked, ARPVP (31) resins toward mononucleotide in aqueous and pyridine media. They claimed that hydrogen-bonding was important between the resins and nucleotides under their conditions. 

Flavin Mononucleotide (FMN) (C17H21N409P) is a phosphoric ester of riboflavin that constitutes the cofactor of various flavoproteins. 

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