Uridine monophosphate , synthesis

The major intermediates in the biosynthesis of nucleic acid components are the mononucleotides uridine monophosphate (UMP) in the pyrimidine series and inosine monophosphate (IMP, base hypoxanthine) in the purines. The synthetic pathways for pyrimidines and purines are fundamentally different. For the pyrimidines, the pyrimidine ring is first constructed and then linked to ribose 5 -phosphate to form a nucleotide. By contrast, synthesis of the purines starts directly from ribose 5 -phosphate. The ring is then built up step by step on this carrier molecule. 

One is from glucose 1-phosphate and the other is from uridine monophosphate (UMP). The pyrophosphate that is liberated from the terminal phosphates of UTP is hydrolyzed to inorganic phosphate by the enzyme pyrophosphatase. This hydrolysis, which is irreversible, drives the reaction in the direction of UDP-glucose synthesis. 

Although no recent activity has been reported in this field, it remains possible that more potent inhibitors of this enzyme have potential applications as anticancer therapeutics. It is also possible that the combination of salvage uridine-cytidine monophosphate synthesis inhibitors with inhibitors of de novo uridine-cytidine monophosphate synthesis (such as PALA or pyrazofurin) may result in more efficacious cancer therapeutics. 

All susceptible fungi are capable of deaminating flucytosine to 5-fluorouracil, a potent antimetabolite that is used in cancer chemotherapy. Fluorouracil is metabolized fast to 5-fluorouracil-ribose monophosphate (5-FUMP) by the enzyme uracil phosphodbosyi transferase (UPRTase, also called uridine monophosphate pyrophosphorylase). As in mammalian cells, 5-FUMP then is either incorporated into RNA (via synthesis of 5-fluorouridine triphosphate) or metabolized to 5-fluoro-2 -5 deoxyuridine-5-monophos-phate (5-FdUMP), a potent inhibitor of thymidylate synthetase. DNA synthesis is impaired as the ultimate inhibition of this latter reaction. The selective action of flucytosine is due to the lack or low levels of cytosine deaminase in mammalian cells, which prevents metabolism to fluorouracil. 

This monosaccharide is transformed to the characteristic disaccharide as follows. It is first covalently united to a C55 isoprenoid alcohol in the plasma membrane, releasing uridine monophosphate (Higashi, Strominger and Sweeley, 1967). A molecule of A-acetylglucosamine is then incorporated, and five glycine residues are added to the lysine residue (this is done in the reverse direction to normal peptide synthesis, and without recourse to ribosomes). The product is usually referred to as the disaccharide decapeptide . 

K54 Krooth, R. S. Regulation of uridine 5 -monophosphate synthesis in human diploid cells. Symp. Int. Soc. Cell Biol., 9, 43-68 (1971)... 

Sarma, D. S. R. and Sidransky, H. Studies on orotic acid fatty liver influence of uridine monophosphate (UMP) on fatty acid synthesis. Fed. Proc., 26, 624 (1967)... 

One-pot synthesis of nucleotide sugars was also demonstrated for multi-enzyme systems as shown for UDP-Gal [107, 108] and dTDP-2-deoxy-Glc [109]. Even some modified sugar nucleotides were synthesized in an one-pot fashion, namely UDP-carba-sugars based on Gal, GlcNAc, Glc, and Man [110]. The cascade involved uridine monophosphate (UMP)-kinase and acetate kinase to generate uridine triphosphate (UTP) as well as Glc-l-P-uridyltransferase, Gal-l-P-uridyltransferase,... 

Fig. 23.1. Pyrimidine pathways Pathways for the de novo synthesis, interconversion, and breakdown of pyrimidine ribonucleotides, indicating their metabolic importance as the essential precursors of the pyrimidine sugars and, with purines, of DNA and RNA. Note that in contrast to purines salvage takes place at the nucleoside not the base level in human cells and pyrimidine metabolism normally lacks any detectable end-product. The importance of this network is highlighted by the variety of clinical symptoms associated with the possible enzyme defects indicated. 23.10, Uridine monophosphate synthase (UMPS), 23.11a, uridine monophosphate hydrolase 1 (UMPHl), 23.12, thymidine phosphorylase (TP), 23.13, dihydropyrimidine dehydrogenase (DPD), 23.14, dihydropyrimidine amidohydrolase (DHP), 23.15, y -ureidopropionase (UP) (23.11b, UMPH superactivity specific to fibroblasts is not shown). CP, carbamoyl phosphate. The pathological metabolites used as specific markers in differential diagnosis are highlighted...

A similar strategy was used for the synthesis of a phenyl phosphotriester of cyclic uridine monophosphate (cUMP) ... 

Shaw synthesis, 3, 109 Uridine, 2 -deoxy-5-iodo-as pharmaeeutical, 1, 160 Uridine 5 -monophosphate biosynthesis, 1, 88 Uridylic acids occurrence, 3, 142 Urispas... 

While mammahan cells reutilize few free pyrimidines, salvage reactions convert the ribonucleosides uridine and cytidine and the deoxyribonucleosides thymidine and deoxycytidine to their respective nucleotides. ATP-dependent phosphoryltransferases (kinases) catalyze the phosphorylation of the nucleoside diphosphates 2 "-de-oxycytidine, 2 -deoxyguanosine, and 2 -deoxyadenosine to their corresponding nucleoside triphosphates. In addition, orotate phosphoribosyltransferase (reaction 5, Figure 34-7), an enzyme of pyrimidine nucleotide synthesis, salvages orotic acid by converting it to orotidine monophosphate (OMP). 

Although FdUrd produces only DNA-medicated cyotoxicity, 5-FU can also be metabolized to fluorouracil monophosphate (FUMP) and ultimately to fluorouracil triphosphate (FUTP), which can be incorporated into RNA in place of uridine triphosphate (UTP). In other words, incorporation of 5-FU into RNA mimics uracil de novo synthesis and affects the production of ribosomal RNAs (rRNAs) (16,17). 5 -FU also affects several aspects of messenger RNA (mRNA) function, including transcription (18), translation (19), and slicing (20). 

The common pyrimidine ribonucleotides are cytidine 5 -monophosphate (CMP cytidylate) and uridine 5 -monophosphate (UMP uridylate), which contain the pyrimidines cytosine and uracil. De novo pyrimidine nucleotide biosynthesis (Fig. 22-36) proceeds in a somewhat different manner from purine nucleotide synthesis the six-membered pyrimidine ring is made first and then attached to ribose 5-phosphate. Required in this process is carbamoyl phosphate, also an intermediate in the urea cycle (see Fig. 18-10). However, as we noted... 

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