Coenzymes nucleotide triphosphate

APH). Chloramphenicol is attacked by chloramphenicol acetyltransferases (CAT). Acetyltransferases attack susceptible amino groups and require acetyl coenzyme A, while AAD or APH enzymes attack susceptible hydroxyl groups and require ATP (or another nucleotide triphosphate). 

The reduced DNA synthesis observed in vitamin Bn-deficient cells is not only due to the low RNR activity responsible for the synthesis of deoxyribo-nucleotide triphosphates. It is known (Andreeva, 1974) that CHsCbl is involved in the synthesis of the thymine intermediate of DNA. In vitamin Bi2-deflcient cells the DNA content increased upon adding thymine to the medium, which had no effect in the case of Bn -cells (Fig. 5.9, Table 5.3) (Iordan et al, 1979a). It follows, then, that the DNA of propionic acid bacteria is linked with Bi2-coenzymes in two ways through the synthesis of deoxyribosides and through the synthesis of thymine. In addition, we suggest that there is a third type of this connection, mediated by DNA methylation. 

Study of the metabolism, fundamental and vital to living things, has led to a detailed understanding of the processes involved. A complex web of enzyme-catalysed reactions is now apparent, which begins with carbon dioxide and photosynthesis and leads to, and beyond, diverse compounds called primary metabolites, e.g. amino acids, acetyl-coenzyme A, mevalonic acid, sugars, and nucleotides [2, 3]. Critical to the overall energetics involved in metabolism is the coenzyme, adenosine triphosphate (ATP), which serves as a common energy relay and co-operates, like other coenzymes, with particular enzymes in the reactions they catalyse. 

ATP and the other nucleoside triphosphate coenzymes not only transfer phosphate residues, but also provide the nucleotide components for this type of activation reaction. On this page, we discuss metabolites or groups that are activated in the metabolism by bonding with nucleosides or nucleotides. Intermediates of this type are mainly found in the metabolism of complex carbohydrates and lipids. 

The synthesis of purine nucleotides (1) starts from IMP. The base it contains, hypoxanthine, is converted in two steps each into adenine or guanine. The nucleoside monophosphates AMP and CMP that are formed are then phos-phorylated by nucleoside phosphate kinases to yield the diphosphates ADP and GDP, and these are finally phosphorylated into the triphosphates ATP and CTP. The nucleoside triphosphates serve as components for RNA, or function as coenzymes (see p. 106). Conversion of the ribonucleotides into deoxyribo-nucleotides occurs at the level of the diphosphates and is catalyzed by nucleoside diphosphate reductase (B). 

The earliest applications of bioaffinity chromatography involved its use in enzyme purification (see Figure 13.7) [7]. Enzyme purification has continued to be a major application of this technique [57]. Some ligands that are employed for this purpose are enzyme inhibitors, coenzymes, substrates, and cofactors. Examples include methods that use nucleotide mono-, di-, and triphosphates for the... 

The following classes of phosphorus-containing compounds were not affected by large amounts of the enzyme with Mg2+, Mn2+, Zn2+, or Co2+ at either pH 9.1 or 7.5 (1) ribo- or deoxyribonucleoside mono-, di-, or triphosphates (2) ribo- or deoxyribopolynucleotides (3) nucleotide coenzymes (e.g., DPN+, UDP-glucose) (4) phosphomonoesters (e.g., glucose-6-P, p-nitrophenyl phosphate) (5) cyclic tri- or tetrametaphos-phates (6) phosphorofluoridates (inorganic phosphorofluoridate, adenosine 5 -phosphorofloridate) and (7) phosphonates (e.g., methylene-bis-phosphonate) (12, 57). 

In addition to their role in the formation of DNA and RNA (see Section 27.2), nucleotides have other important biological functions. For example, adenosine triphosphate (ATP) is an important energy carrier in biochemical reactions, and nicotinamide adenine dinucleotide is a coenzyme that is often involved in biochemical oxidation-reduction reactions. 

Urease catalyzes the hydrolysis of urea to ammonia, while catalase is capable of rapidly decomposing II2O2 to H2O + 02. " In a number of cases, enzyme catalysis requires the participation of a smaller molecule usually referred to as a coenzyme. Many of the vitamins and simple nucleotides such as adenosine triphosphate (ATP) have been shown to act as coenzymes. 

Ribonucleotide reductases with an absolute requirement for adenosyl-cobalamin (Fig. 1) as a coenzyme have been demonstrated only in microorganisms (7). These reductases may be classified into two groups based on the nature of the nucleotide substrate utilized ribonucleoside triphosphate reductases, which act upon the ribonucleoside triphosphates... 

Scheme 22 The whole biosynthetic pathway of sugar nucleotides. ATP, adenosine triphosphate Gal-1 -P, galactose-1-phosphate UTP, uridine triphosphate UDP, uridine diphosphate NAD, nicotinamide adenine dinucleotide Fru, fructose AcCoA, acetyl coenzyme-A PEP, phosphoenolpyruvate CTP, cytidine triphosphate NADP, nicotinamide adenine dinucieotide phosphate GTP, guanosine triphosphate.

The earliest use of affinity chromatography and its most popular application is in the purification of proteins and other biological agents. The use of this method in enzyme purification is particularly important, with hiuidreds to thousands of applications having been reported in this field alone. Ligands used for this piupose include enzyme inhibitors, coenzymes, substrates, and cofactors. For instance, nucleotide mono-, di-, and triphosphates can be used for the purification of various kinases, NAD has been used to isolate dehydrogenases, and RNA or DNA has been used for the preparation of polymerases and nucleases. 

Nucleosides and nucleotides are found in places other than as part of the structure of DNA and RNA. We have seen, for example, that adenosine units are part of the structures of two important coenzymes, NADH and coenzyme A. The 5 -triphosphate of adenosine is, of course, the important energy source, ATP (Section 22. IB). The compound called 3, 5 -cyclic adenylic acid (or cyclic AMP) (Fig. 25.6) is an important regulator of hormone activity. Cells synthesize this compound from ATP through the action of an enzyme, adenylate cyclase. In the laboratory, 3, 5 -cyclic adenylic acid can be prepared through dehydration of 5 -adenylic acid with dicyclohexylcarbodiimide. 

Di-n-butylphosphinothioyl bromide has been introduced as a reactant in nucleoside chemistry high yields of nucleoside di- and triphosphates, 3, 5 -cyclic phospates, and nucleotide coenzymes have been obtained... 

Acid-soluble extracts can be assayed for certain nucleotides by enzymatic methods. Various assay procedures for the adenosine phosphates and the pyridine nucleotide coenzymes are available 22,33). Specific methods for the determination of picomole amounts of the four deoxyribonucleoside triphosphates have been reported recently 15,16). 

The phosphates of the four ribonucleosides represented in RNA are found in virtually all cells, with erythrocytes being exceptional in that not all four ribonucleosides are represented in some nonnucleated cells. Nucleotide coenzymes and conjugated nucleotides are present in patterns which are characteristic of the tissue sample. These compounds are all nucleoside 5 -phosphate esters and the triphosphates are the most abundant species under conditions adequate for the mainteiiance of cellular energy metabolism. The nucleotide composition of a variety of animal tissues is discussed by Mandel (22) we will consider only several. 

Nucleotide coenzymes involved in group-transfer reactions (see below, Section IV) and similar compounds are frequently formed by reaction of a nucleoside triphosphate with a phosphorylated compound to give pyrophosphate and a product of the type, nucleoside diphospho-X. Pyro-... 

Purines and pyrimidines are functionally operative as nucleotide derivatives. These are present as intracellular pool ingredients and are used as major components of nucleic acids, as well as many coenzymes. Regulation of a variety of metabolic processes is required to ensure optimal amounts and a balanced distribution of the many different forms purine and pyrimidine classes, ribose and deoxyribose derivatives, and mono-, di-, and triphosphates. 

The enzyme mechanism for DNA synthesis was clarified by Kornberg and his associates [103-108] in bacterial systems. A single DNA strand is a polynucleotide chain in which the individual nucleotides are linked by ester bonds between the carbon 3 of one deoxyri-bose and the carbon 5 of another deoxyribose belonging to an immediately adjacent nucleotide. There are two distinct aspects in the synthesis of a single strand formation of the ester bond and the alignment of the nucleotide in the proper sequence. On the basis of observations made on the biosynthesis of coenzymes, Kornberg postulated that the precursor used for the formation of the polynucleotide chain was an activated 5 -mononucleotide, namely, a triphosphate. 

The nucleotide coenzymes are structurally related to the mononucleotides. Typical nucleotide coenzymes are adenosine triphosphate (ATP), flavin-adenine-dinucleotide (FAD) and numerous other phosphate esters of complex structure, containing adenosine, guanosine, cytidine or uridine. Five coenzymes are known for example, which are derived from cytidine diphosphate (CDP) CDP-choline, CDP-ethanolamine, CDP-diglyceride, CDP-glycerol and CDP-ribitol. 

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