Nucleoside monophosphate phosphorylation

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. 

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 monophosphates are converted to their triphosphates by enzymatic phosphorylation reactions. Ribonucleotides are converted to deoxyribonucleotides by ribonucleotide reductase, an enzyme with novel mechanistic and regulatory characteristics. The thymine nucleotides are derived from dCDP and dUMP. 

Adenylate kinase performs the essential function of recovering AMP formed by many enzymatic processes and converting it to ADP (Eq. 6-65) which can be reconverted to ATP by oxidative or substrate level phosphorylation. The enzyme is present in all organisms. In vertebrates different isoenzymes function in the cytosol, mitochondrial intermembrane space, and mitochondrial matrix.862 863 A group of other nucleotide and deoxynucleotide kinases convert nucleoside monophosphates into diphosphates.864 865 Some of them, e.g., uridylate kinase are similar in structure and properties to adenylate kinase.866 867 Another member of the adenylate kinase family is phosphoribulokinase, an important photosynthetic enzyme (see Fig. 17-14, step a).868... 

The authors experience is that the enzymic phosphorylation and diphosphorylation of nucleoside monophosphates is very efficient the yields are nearly quantitative and the immobilized enzyme system appears reusable for at least three months. 

The compound 5-fluorouridine targets thymidylate synthase. After a nucleoside kinase phosphorylates it, resembles the natural substrate for the enzyme, except that it contains a fluorine where dUMP has a hydrogen. The fluorine isn t removed from the ring by thymidylate synthase, and this causes the ring to remain covalently bound to the enzyme, which means that the enzyme is irreversibly inactivated. The 5-fluorouridine monophosphate is an example of a suicide substrate —a compound whose reaction with an enzyme causes the enzyme to no longer function. 

Although there are many methods available, there are two main routes for the synthesis of nucleoside monophosphates. These involve either the reaction of the nucleoside with 2-cyanoethylphosphate in the presence of a condensing agent such as dicyclohexyl carbodiimide (DCC)2,3 or phosphorylation of the nucleoside... 

The phosphorylation of free nucleosides using phosphoryl chloride in trimethyl-phosphate to give a nucleoside phosphorodichloridate is known as the Yoshikawa procedure4 (Protocol 5). Hydrolysis of this intermediate in aqueous TEAB provides a route to nucleoside 5 -monophosphates (Protocol 8) although it is mainly used to prepare nucleoside triphosphates, whereby pyrophosphate is reacted with the nucleoside intermediate (see Section 3.3 and Protocol 10). In practice, a compromise between formation of the 5 -phosphorodichloridate that is,... 

Nucleoside Monophosphate Kinases Catalyzing Phosphoryl Group Exchange between Nucleotides Without Promoting Hydrolysis... 

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. 

Tenofovir is a nucleotide (nucleoside monophosphate) analogue reverse transcriptase inhibitor, given as a prodrug, tenofovir disoproxU fumarate. In contrast to the other members of this class, it only needs to be phosphorylated twice intraceUularly before it is pharmacologically active. Adverse effects have been reported as flatulence, raised transaminases, raised creatine kinase activity, and rarely a raised serum creatinine (1). Tenofovir does not currently appear to be nephrotoxic. 

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... 

Phosphorylation of nucleosides. Direct phosphorylation of unprotected nucleosides generally leads to a mixture of the three possible phosphates. However, treatment of 2, 3 -0-isopropylidene nucleosides with phosphoryl chloride gives. V-phosphorodichloridates in fair yield. The reaction is greatly improved by use of trimethyl phosphate, (CH30)3P0, ortriethyl phosphate, in which the substrates are moderately soluble. After hydrolysis, 5 -nucleotides are obtained in nearly quantitative yield.1 Adenine nucleosides, such as (1), are readily converted into the 3, 5 -cyclic monophosphate, such as (2), by this procedure.2... 

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