Nucleoside monophosphate kinase triphosphates

All of these triphosphates take part in phosphorylations in the cell. Similarly, specific nucleoside monophosphate kinases catalyze the formation of nucleoside diphosphates from the corresponding monophosphates. 

Strominger, J,L. Heppel, L.A. Maxwell, E.S. Nucleoside monophosphate kinases. Transphosphorilation between adenosine triphosphate and nucleoside monophosphates. Biochim. Biophys. Acta, 32, 412-421 (1959)... 

Nucleoside diphosphates (NDP) are synthesized from the corresponding nucleoside monophosphates (NMP) by base-specific nucleoside monophosphate kinases (Figure 22.9). [Note These kinases do not discriminate between ribose or deoxyribose in the substrate.] ATP is generally the source of the transferred phosphate, because it is present in higher concentrations than the other nucleoside triphosphates. Adenylate kinase is particularly active in liver and muscle, where the turnover of energy from ATP is high. Its function is to maintain an equilibrium among AMP, ADP, and ATP. Nucleoside diphosphates and triphosphates are interconverted by nucleoside diphosphate kinase—an enzyme that, unlike the monophosphate kinases, has broad specificity. 

Nucleoside diphosphates (NDP) are synthesized from the corresponding nucleoside monophosphates (NMP) by base-specific nucleoside monophosphate kinases. NDPs and nucleoside triphosphates (NTP) are interconverted by nucleoside diphosphate kinase—an enzyme that, unlike the monophosphate kinases, has broad specificity. 

Figure 2 Synthesis of nucleoside triphosphates (1) Adenylate kinase (EC 2.1 A3, N = A,C,U) or guanylate kinase (EC 2.7.4.8, N = G), or nucleoside monophosphate kinase (EC 2.7.4.4, N = U). (2) Pyruvate kinase (EC 2.7.1.40). NMP, nucleoside monophosphate NDP, nucleoside diphosphate NTP, nucleoside triphosphate. (From Ref. 12.)...

Figure 9.45. Phosphoryl Group Transfer by Nucleoside Monophosphate Kinases. These enzymes catalyze the interconversion of a nucleoside triphosphate (here, ATP) and a nucleoside monophosphate (NMP) into two nucleoside diphosphates by the transfer of a phosphoryl group (shown in red).

How is the other major pyrimidine ribonucleotide, cytidine, formed It is synthesized from the uracil base of UMP, but UMP is converted into UTP before the synthesis can take place. Recall that the diphosphates and triphosphates are the active forms of nucleotides in biosynthesis and energy conversions. Nucleoside monophosphates are converted into nucleoside triphosphates in stages. First, nucleoside monophosphates are converted into diphosphates by specific nucleoside monophosphate kinases that utilize ATP as the phosphoryl-group donor (Section 9.4). For example, UMP is phosphorylated to UDP by UMP kinase. 

Some biosynthetic reactions are driven by the hydrolysis of nucleoside triphosphates that are analogous to ATP—namely, guanosine triphosphate (GTl ), uridine triphosphate (UTP), and cytidine triphosphate (CTP). The diphosphate forms of these nucleotides are denoted by GDP, UDP, and CDP, and the monophosphate forms are denoted by GMP, UMP, and CMP. Enzymes catalyze the transfer of the terminal phosphoryl group from one nucleotide to another. The phosphorylation of nucleoside monophosphates is catalyzed by a family of nucleoside monophosphate kinases, as discussed in Section 9.4. The phosphorylation of nucleoside diphosphates is catalyzed by 7iucleoside diphosphate kinase, an enzyme with broad... 

Scheme L Synthesis of a2,64inked sialyl-N-acetyllactosamine using a one-pot multi-enzyme system with in situ regeneration of CMP-Neu5Ac. Abbreviations for enzymes CSS, CMP-sialic acid synthetase NMK, nucleoside monophosphate kinase PK, pyruvate kinase PPase, pyrophosphatase. Abbreviations for compounds PEP, phosphoenolpyruvate ADP, adenosine 5 -diphosphate ATP, adenosine 5 -triphosphate CMP, cytidine 5-monophosphate CDP, cytidine 5 -diphosphate CTP, cytidine 5-triphosphate LacNAc, N-acetyllactosamine NeuSAc, N-acetylneuraminic acid PPi, inorganic pyrophosphate.

Other nucleoside triphosphate are synthesized in ATP-requiring reactions catalyzed by a series of nucleoside monophosphate kinases ... 

AMP and GMP can be phosphorylated to the di- and triphosphate levels. The production of nucleoside diphosphates requires specific nucleoside monophosphate kinases, whereas the production of nucleoside triphosphates requires nucleoside diphosphate kinases, which are active with a wide range of nucleoside diphosphates. The purine nucleoside triphosphates are also used for energy-requiring processes in the cell and also as precursors for RNA synthesis (see Fig. 41.2). 

Nucleoside monophosphate kinases have been isolated which are specific for adenylate as the phosphoryl acceptor, but will accept various nucleoside triphosphates as phosphoryl donors. Such an enzyme activity was partly purified from hog kidney by Gibson et at. 20). Heppel et al. 21) have separated a phosphokinase activity from calf liver which accepts only adenylate as the nucleoside monophosphate substrate, but uses ATP, GTP, CTP, UTP, or ITP as the phosphate donor. 

This enzyme activity is widely distributed in nature, and tissues generally show a higher concentration of this activity than of nucleoside monophosphate kinases. The enzyme has broad specificity purified preparations appear to have only the requirement that the substrates be a nucleoside triphosphate and a nucleoside diphosphate. 

Aspartate carbamyltransferase 2 dihydroorotase 3 orotate reductase 4 orotate phosphoribosyl-transferase 5 orotidine-5 -phosphate decarboxylase 6 cytidylate kinase, nucleotide diphosphate kinase 7 cytidine triphosphate synthetase 8 nucleoside monophosphate kinase, ribonucleoside diphosphate reductase, phosphatase 9 thymidylate synthase... 

The addition of a third phosphate to any of the nucleoside pyrophosphates, such as UDP, is catalyzed by an enzyme found in yeast and several animal tissues. Since the reaction catalyzed by this enzyme appears to be nonspecific with respect to the base of the nucleotides, it has been named nucleoside diphosphate kinase (nudiki). The phosphate donor in this reaction may be any of the nucleoside triphosphates. As in the case of the nucleoside monophosphate kinases, there are no significant differences in the free energies of hydrolysis of the various nucleoside triphosphates, so all of the reactions are freely reversible with equilibrium constants near 1. Since the phosphorylation of nucleoside diphosphates is reversible, it is necessary that each of the corresponding triphosphates serve as phosphate donor. The phosphorylation of the monophosphates is similarly reversible, but in this case one of the sites on the enz3one appears to react only with adenine, and involves the conversion of ATP to ADP. The complementary reaction involves XMP XDP. Thus the nonadenine nucleotides are never equivalent to ATP, and the reaction is limited to the phosphorylation of a specific nucleoside monophosphate by ATP. 

An enzyme partially purified from yeast acts upon the nucleotides of adenine, guanine, and uridine to carry out transphosphorylation (Eqs. 33) to 36)] 112-116). Nucleoside monophosphate kinases have been partially purified from E. coli, which catalyzes the formation of triphosphates of deoxyadenine, deoxyguanosine, thymidine, and deoxycytidine from their corresponding 5 -monophosphates, in the presence of ATP 116, 117). 

Entecavir, telbivudine, clevudine, and the other nucleoside analogues (Fig. 4aa) need to be phosphorylated to their 5 -triphosphate form to be antivirally active (Fig. 8). This again implies three phosphorylation steps based successively on a nucleoside kinase, nucleoside 5 -monophosphate kinase, and nucleoside 5 -diphosphate kinase. These reactions have been characterized only in a few cases, that is, thymidylate kinase in the metabolism of clevudine (Hu et al. 2005). 

In the preceding sections the conversion of purines and purine nucleosides to purine nucleoside monophosphates has been discussed. The monophosphates of adenosine and guanosine must be converted to their di- and triphosphates for polymerization to RNA, for reduction to 2 -deoxyribonucleoside diphosphates, and for the many other reactions in which they take part. Adenosine triphosphate is produced by oxidative phosphorylation and by transfer of phosphate from 1,3-diphosphoglycerate and phosphopyruvate to adenosine diphosphate. A series of transphosphorylations distributes phosphate from adenosine triphosphate to all of the other nucleotides. Two classes of enzymes, termed nucleoside mono-phosphokinases and nucleoside diphosphokinases, catalyse the formation of the nucleoside di- and triphosphates by the transfer of the terminal phosphoryl group from adenosine triphosphate. Muscle adenylate kinase (myokinase)... 

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). 

Nucleoside diphosphates and triphosphates are interconverted by nucleoside diphosphate kinase, an enzyme that has broad specificity, in contrast with the monophosphate kinases. X and Y can represent any of several ribonucleosides or even deoxyribonucleosides. 

Adenylate kinase, which in vivo catalyzes the equilibrium between adenosine mono-, di- and triphosphates, has been used extensively in the production of ATP (27, 41). Although the enzyme has a broad substrate specificity for nucleoside di- and triphosphates, the specificity for monophosphates is much more restrictive. Nonetheless, the specificity is... 

Nucleoside monophosphates are synthesized de novo in the course of Purine biosynthesis (see) and Pyrimidine biosynthesis (see). They are then phosphoryla-ted stepwise by the action of kinases, to produce nucleoside di- and triphosphates. The 2-deoxyribose moiety is formed by reduction of the ribose in ribonucleotides (see Ribonucleotide reductase). Reduction of free ribose to 2-deoxyribose does not occur in vivo. 

The nucleoside monophosphates are converted to the triphosphates (the direct precursors of RNA) by two kinase reactions These kinases have a low specificity, and they catalyse the phosphorylation of nucleotides of adenine, guanine and the pyrimidines (Fig. 3). An alternative route for the synthesis of purine nucleotides is the Salvage pathway (see). 

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