Nucleotides precursors

Although the 3 - and 5 -polyphosphate derivatives mentioned above exhibit exquisite inhibitory potency these compounds are not cell permeable. To take advantage ofthepotency of such derivatives for studies with intact cells and tissues, there are two possibilities. One is chemically to protect the phosphate groups from exonucleotidases that also allows the compound to transit the membrane intact. The other is to provide a precursor molecule that is cell permeable and is then metabolized into an inhibitor by intracellular enzymes. The general term for such a compound is prodrug nucleotide precursors are also referred to as pronucleotides. Families of protected monophosphate derivatives were synthesized, based on (3-L- and 3-D-2, 5 -dd-3 -AMP, 3-L-2, 3 -dd-5 -AMP, and the acyclic 9-substituted adenines, PMEA and PMPA. Protective substituents were (i) -( -pivaloyl-2-thioethyl) ... 

Bioassays of related substances can be quite similar in design. Specific growth factors, for example, stimulate the accelerated growth of specific animal cell lines. Relevant bioassays can be undertaken by incubation of the growth-factor-containing sample with a culture of the relevant sensitive cells and radiolabelled nucleotide precursors. After an appropriate time period, the level of radioactivity incorporated into the DNA of the cells is measured. This is a measure of the bioactivity of the growth factor. 

Metabolism 5-FU must be converted into a nucleotide precursor (5FdUMP or 5FdUTP to interfere with thymidylate synthase or RNA metabolism) Yes, must be metabolized to SN-38 by carboxylesterase... 

The main function of the ester 34 in bacterial cells seems to be its participation in the biosynthesis of the glycopeptide cell-wall polymer. If this process is blocked, there results the accumulation of a high concentration of sugar nucleotide precursors in the cell. A number of these compounds have been isolated the simplest one is the ester of uridine 5 -pyrophosphate with N-acetylmuramic acid [2-acetamido-3-0-(D-l-carboxyethyl)-2-deoxy-D-glucose] (37), first obtained from Staphylococcus aureus cells that had been treated with penicillin7,151 or Gentian Violet.144 An intermediate in the biosynthesis of 37 was isolated and shown to be the 3 -enolpyruvate ether152,153 (38). 

DNA Replication Kornberg and his colleagues incubated soluble extracts of E. coli with a mixture of dATP, dTTP, dGTP, and dCTP, all labeled with 32P in the a-phosphate group. After a time, the incubation mixture was treated with trichloroacetic acid, which precipitates the DNA but not the nucleotide precursors. The precipitate was collected, and the extent of precursor incorporation into DNA was determined... 

Figure 25-14 Assembly of the pyrimidine ring and biosynthesis of the pyrimidine nucleotide precursors of RNA and DNA.

Glaser and Burger, using membrane preparations of several bacterial species and various nucleotide precursors, prepared in vitro a few kinds of teichoic acids which were identical with samples extracted from the cell walls of the studied strains. The following TA chain precursors were used cytidine diphosphate glycerol (CDP-... 

Antimetabolites are structurally related to normal cellular components. They generally interfere with the availability of normal purine or pyrimidine nucleotide precursors by inhibiting their synthesis or by competing with them in DNA or RNA synthesis. Their maximal cytotoxic effects S-phase (and therefore cell-cycle) specific. 

Mode 1. Much more ribose 5-phosphate than NADPH is required. For example, rapidly dividing cells need ribose 5-phosphate for the synthesis of nucleotide precursors of DNA. Most of the glucose 6-phosphate is converted into fructose 6-phosphate and glyceraldehyde 3-phosphate by the glycolytic pathway. Transaldolase and transketolase then convert two molecules of fructose 6-phosphate and one molecule of glyceraldehyde 3-phosphate into three molecules of ribose 5-phosphate by a reversal of the reactions described earlier. The stoichiometry of mode 1 is... 

A useful procedure for estimating adenylate cyclase in intact cells and tissues is to incubate the tissue with labelled adenine and then measure the rate of labelling of cyclic AMP [112]. Adenine readily penetrates cells and is partially converted to ATP. In heart slices, the ATP newly synthesised from radioactive adenine was found in equilibrium with the existing pool used for the production of cyclic AMP the specific activity of the newly-formed cyclic AMP was similar in the presence and in the absence of stimulatory hormone [113]. The prelabelling method has been compared with the protein-binding method in brain slices [114,115]. Increases in total levels of cyclic AMP and increases in levels of radioactive cyclic AMP derived from intracellular adenine nucleotides labelled by prior incubation with radioactive adenine occurred on similar time courses and to similar extents. Radioactive cyclic AMP represented a small (7-13%) but relatively constant fraction of the total amount of cyclic AMP. These results provided no evidence for the presence of more than one major compartment of adenine nucleotides in brain slices that serve as a source of nucleotide precursor for cyclic AMP. The nucleotides of this compartment were uniformly labelled by incubation with radioactive adenine [116]. 

Purines, pyrimidines and their nucleosides and nucleoside triphosphates are synthesized in the cytoplasm. At this stage the antifolate drugs (sulphonamides and dihydrofolate reductase inhibitors) act by interfering with the synthesis and recycling of the co-factor dihydrofolic acid (DHF). Thymidylic acid (2-deoxy-thymidine monophosphate, dTMP) is an essential nucleotide precursor of DNA synthesis. It is produced by the enzyme thymidylate synthetase by transfer of a methyl group from tetrahydrofolic acid (THF) to the uracil base on uridylic acid (2-deoxyuridine monophosphate, dUMP) (Fig. 12.5). THF is converted to DHF in this process and must be reverted to THF by the enzyme dihydrofolate reductase (DHFR) before... 

J3. Jones, 0. W., Jr., Ashton, D. M., and Wyngaarden, J. B., Accelerated turnover of phosphoribosylpyrophosphate—a purine nucleotide precursor in certain gouty subjects. J. Clin. Invest. 41, 1805-1815 (1962). 

These nucleotide precursors, also protected at the 5 or 3 position with a photolabile protecting group, are applied to the substrate, where they react with the surface hydroxyl groups in the pre-irradiated regions. The monomer coupling step is carried out in the presence of a suitable activator, such as tetrazole or di-... 

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