Gene/Protein Disease Symptom Drug Enzyme Compound
Pivot Concepts: Gene/Protein Disease Symptom Drug Enzyme Compound   Target Concepts: Gene/Protein Disease Symptom Drug Enzyme Compound

---

Query: EC:1.5.1.3 (dihydrofolate reductase)
5,819 document(s) hit in 31,850,051 MEDLINE articles (0.00 seconds)

Leishmania tropica promastigotes have been selected which are highly resistant to the thymidylate synthetase (TS) inhibitor, 10-propargyl-5,8-dideazafolate (CB3717). As reported for L. tropica resistant to methotrexate (MTX), an inhibitor of dihydrofolate reductase (DHFR), CB3717-resistant organisms have high levels of the bifunctional TS-DHFR and amplified DNA sequences. TS-DHFR represents up to 2% of the protein in cell extracts and does not appear to have a structural alteration that contributes to drug resistance. The amplified unit of DNA has a uniform restriction-site map throughout the selection and is nearly identical to the 30 kb amplified unit of R-region DNA found in MTX-resistant cells, except for a small increase in size of the fragment that contains a junction believed to be the site of DNA rearrangements generated during amplification. CB3717-resistant cells do not possess the amplified H-region DNA found in MTX-resistant cells. The amplified DNA in cells resistant to low levels of CB3717 appears as a 30-kb extrachromosomal circle, similar to the amplified DNA of MTX-resistant organisms. In cells resistant to higher levels of drug, the amplified DNA appeared as higher molecular weight forms. When resistant cells were grown in the absence of drug, the amplified DNA and levels of TS-DHFR gradually fell to approximately 10% of the resistant levels. These findings support the proposal that the R-region DNA possesses the sequences that encode the bifunctional protein.
...
PMID:Selection and properties of Leishmania tropica resistant to 10-propargyl-5,8-dideazafolate, an inhibitor of thymidylate synthetase. 405 89

The activities of six bacteriophage T2r(+)-induced enzymes (thymidylate synthetase, deoxycytidylate deaminase, thymidylate kinase, deoxycytidylate hydroxymethylase, deoxycytidine pyrophosphatase, and dihydrofolate reductase) were measured after dilution of phage-infected Escherichia coli B from 8 x 10(8) to 2 x 10(8) cells per ml. The only enzyme activity altered was that of deoxycytidylate deaminase, which increased three- to fourfold. Conversely, the rapid concentration of cells from 2 x 10(8) to 8 x 10(8) per ml did not result in a reduction in deaminase activity. Although an enhancement in aeration reduced the response of deoxycytidylate deaminase to cellular dilution, the influence of potential metabolic inhibitors or activators could not be shown. The change in deoxycytidylate deaminase activity appeared to be associated with an altered translational event, since the increase could not be prevented by rifampin but was blocked effectively by chloramphenicol and hydroxylamine. In addition, antibody to the T2 phage-induced deoxycytidylate deaminase demonstrated that the increase in enzyme activity was associated with a corresponding increase in radioactive leucine incorporated into the enzyme antigen.
...
PMID:Relationship between Escherichia coli B titer and the level of deoxycytidylate deaminase activity induced on bacteriophage T2r + infection. 433 61

The kinetic order of synthesis of deoxycytidylate deaminase (EC 3.5.4.12), deoxycytidylate hydroxymethylase (EC 2.1.2.b), dihydrofolate reductase (EC 1.5.1.3), 5-hydroxymethyldeoxycytidylate kinase (EC 2.7.4.4), and thymidylate synthetase (EC 2.1.1.b) after infection of Escherichia coli with T2r(+) bacteriophage was found not to correlate with their order of synthesis in an in vitro protein-synthesizing preparation. The in vivo and in vitro synthesis of enzyme-specific messenger RNA measured in the protein-synthesizing preparation preceded each enzyme by about 1 min. Through the use of sheared DNA, it was shown that the thymidylate synthetase gene was most susceptible to a loss in template activity, which suggests that this gene is further removed from its promoter than the other genes are from theirs. With a DNA segment of 2.5 x 10(5) daltons, the synthesis of dihydrofolate reductase alone was obtained, but at a much reduced rate. Translation of the RNA from phage-infected cells treated with chloramphenicol yielded amounts of dihydrofolate reductase and deoxycytidylate hydroxymethylase activities similar to those obtained with RNA from untreated infected cells. These results suggest that the chloramphenicol RNA, which consists primarily of immediate-early RNA, may contain most, if not all, of the information required for the synthesis of phage dihydrofolate reductase and deoxycytidylate hydroxymethylase.
...
PMID:The temporal expression of T2r + bacteriophage genes in vivo and in vitro. 455 54

A mutant of bacteriophage T4 was isolated which was unable to induce virus-specific dihydrofolate reductase in infected cells. The mutant was able to form several other early enzymes of pyrimidine metabolism. Growth of the mutant in a wild-type host, Escherichia coli B, was compared with that of the parent strain, T4BO(1), and T4td8, a mutant which lacks the ability to induce thymidylate synthetase. Growth studies were carried out in minimal medium, which gave higher growth rates and phage yields than the supplemented media used in previous studies. The reductase mutant formed deoxyribonucleic acid and plaque-forming particles at a rate slightly higher than the synthetase mutant but 1.5-to 2-fold lower than that of the wild-type phage under all conditions studied. The addition of thymine to a culture infected by the mutant increased the growth rate significantly, suggesting that the genetic lesion leads to a partial thymidylate deficiency. Like other viral genes controlling steps in thymidylate metabolism, the dihydrofolate reductase gene appears to be useful but not completely essential for growth.
...
PMID:Growth of a dihydrofolate reductaseless mutant of bacteriophage T4. 491 41

A method was devised for identifying nonlethal mutants of T4 bacteriophage which lack the capacity to induce degradation of the deoxyribonucleic acid (DNA) of their host, Escherichia coli. If a culture is infected in a medium containing hydroxyurea (HU), a compound that blocks de novo deoxyribonucleotide biosynthesis by interacting with ribonucleotide reductase, mutant phage that cannot establish the alternate pathway of deoxyribonucleotide production from bacterial DNA will fail to produce progeny. The progeny of 100 phages that survived heavy mutagenesis with hydroxylamine were tested for their ability to multiply in the presence of HU. Four of the cultures lacked this capacity. Cells infected with one of these mutants, designated T4nd28, accumulated double-stranded fragments of host DNA with a molecular weight of approximately 2 x 10(8) daltons. This mutant failed to induce T4 endonuclease II, an enzyme known to produce single-strand breaks in double-stranded cytosine-containing DNA. The properties of nd28 give strong support to an earlier suggestion that T4 endonuclease II participates in host DNA degradation. The nd28 mutation mapped between T4 genes 32 and 63 and was very close to the latter gene. It is, thus, in the region of the T4 map that is occupied by genes for a number of other enzymes, including deoxycytidylate deaminase, thymidylate synthetase, dihydrofolate reductase, and ribonucleotide reductase, that are nonessential to phage production in rich media.
...
PMID:Isolation of bacteriophage T4 mutants defective in the ability to degrade host deoxyribonucleic acid. 491 96

The effect of the methotrexate (MTX)-5-fluorouracil (FUra) combination on L1210 cell viability was highly sequence dependent in that a 1.4 log (25-fold) increase in cytotoxicity was observed when the MTX preceded FUra, as compared to the reverse sequence. The formation of ternary complexes of thymidylate synthetase has been examined as a basis for the interaction of FUra and MTX in L1210 cells. L1210 cells converted 39% of the total intracellular MTX into MTX-poly-gamma-glutamates within 4 hours of a 1 microM MTX exposure. MTX-diglutamate (2,4-diamino,N 10-methylpteroyl-diglutamate) and MTX-triglutamate were the predominant metabolites. In contrast to the ternary complexes formed with MTX and MTX-diglutamate, the 5-fluorodeoxy-uridylate (FdUMP)-7,8-dihydropteroylpentaglutamate-enzyme and the FdUMP-5,10-methylenetetrahydropteroylpentaglutamate-enzyme complexes were stable to polyacrylamide gel electrophoresis under nondenaturing conditions. MTX-diglutamate enhanced the extent of tight-binding inhibition of thymidylate synthetase activity by FdUMP in the presence of saturating 5,10-methylenetetrahydropteroylpentaglutamate, suggesting that MTX-diglutamate did not antagonize the formation of FdUMP-5,10-methylenetetrahydropteroylpentaglutamate enzyme complex. We propose that the sequence-dependent effect of MTX plus FUra on L1210 cell viability results from MTX and MTX polyglutamate inhibition of dihydrofolate reductase, and consequently a trapping of intracellular folates as dihydrofolate polyglutamates that could increase the extent of FdUMP binding to thymidylate synthetase.
...
PMID:The role of methotrexate and dihydrofolate polyglutamates in the enhancement of fluorouracil action by methotrexate. 617 21

Trichomonas vaginalis is incapable of de novo pyrimidine biosynthesis because it cannot incorporate bicarbonate, aspartate or orotate into its pyrimidine nucleotides or nucleic acids. The organism can salvage exogenous cytidine greater than uridine greater than uracil and thymidine, and incorporate them into the nucleotide pool. A portion of cytidine is converted to CMP, CDP and CTP by cytidine phosphotransferase and nucleotide kinases. Some cytidine and most of uracil are, however, converted first to uridine by cytidine deaminase and uridine phosphorylase respectively; uridine is then incorporated into UMP, UDP and UTP by uridine phosphotransferase and nucleotide kinases. The two phosphotransferases, found mainly in the non-sedimentable fraction of T. vaginalis, provide the main avenue of pyrimidine salvage. No significant levels of pyrimidine phosphoribosyl transferase or nucleoside kinases can be detected in the extract. T. vaginalis has no appreciable dihydrofolate reductase or thymidylate synthetase; it grows normally in millimolar concentrations of methotrexate, pyrimethamine, or trimethoprim, and cannot incorporate labels from exogenous uracil or uridine into DNA. It has an enzyme thymidine phosphotransferase in the sedimentable fraction which converts thymidine to TMP. Thymidine salvage in T. vaginalis is thus totally isolated from the rest of the pyrimidine salvage.
...
PMID:Salvage of pyrimidine nucleosides by Trichomonas vaginalis. 619 66

Methotrexate (MTX)-resistant human breast cancer cells (MTXR ZR-75) were obtained following serial passage of the wild-type ZR-75-1 cells (wild-type ZR-75) in MTX. The resistant cell line contains neither quantitative nor qualitative changes in dihydrofolate reductase compared to the parental line. Resistance is associated with a 3-fold decrease in MTX transport into MTXR ZR-75 cells as well as a 3-fold decrease in the activity of thymidylate synthetase in the resistant subline. Moreover, marked differences were observed between the wild-type and MTXR ZR-75 cells in their ability to convert MTX to its polyglutamate derivatives. Wild-type ZR-75 cells accumulate significant intracellular levels of antifolates during prolonged (24 h) exposure to 2 microM MTX, due to the formation of MTX polyglutamates. In contrast, essentially no polyglutamates are formed in the MTXR cells even during conditions which result in a vast excess of free intracellular drug in these cells. This defect is not associated with any apparent change in the activity of the enzyme folylpolyglutamyl synthetase, nor is there any alteration in the apparent Km of this enzyme for MTX in the resistant cells. Further studies demonstrate that the MTXR ZR-75 cells are cross-resistant to antifolate analogues which can be converted to polyglutamate derivatives (aminopterin and dichloromethotrexate), yet they are relatively sensitive to antifolate analogues such as 2,4-diamino-5-(3',4'-dichlorophenyl)-6-methylpyrimidine, triazinate, and trimetrexate, which cannot be converted to polyglutamate forms. These studies identify a new mechanism (diminished accumulation of MTX polyglutamates) associated with resistance to MTX and lend additional support to the hypothesis that the formation of these derivatives is an important determinant of MTX cytotoxicity.
...
PMID:A methotrexate-resistant human breast cancer cell line with multiple defects, including diminished formation of methotrexate polyglutamates. 620 61

The effects of various inhibitors of DNA precursor metabolism were studied on Dictyostelium discoideum growing in a defined axenic medium. Fluorodeoxyuridine was an effective inhibitor of growth at 20 micrograms/ml; this inhibition was not reversed by thymidine, suggesting that in this organism fluorodeoxyuridine is not acting on thymidylate synthetase alone. Removal of the required nutrient, folic acid, from the medium resulted in a lower maximum level of growth than in the control. The inclusion of adenine, guanine, serine, and thymidine in the minus-folic acid medium allowed the final growth level to approach that of the control. Methotrexate, a folic acid analog and dihydrofolate reductase inhibitor, blocked growth completely at 200 micrograms/ml; its effect was partly reversed by the addition of adenine, guanine, serine, and thymidine. Aminopterin, another folic acid analog, had only a temporary effect on cell multiplication, followed by a return to exponential growth. Trimethoprim was ineffective up to 200 micrograms/ml. Hydroxyurea blocked growth in the concentration range of 150 to 300 micrograms/ml. These results indicate that several of these inhibitors are effective for altering thymidine monophosphate synthesis in D. discoideum and hence may be useful for studies of DNA replication and repair and for the isolation and characterization of thymidine-requiring mutants.
...
PMID:Inhibitors of DNA precursor metabolism in Dictyostelium discoideum. 621 97

Thymidylate synthetase levels in five human gastrointestinal tumor cell lines (two colon, two colorectal, one stomach) were determined. Titration of the enzyme in cell cytosol using the active-site titrant, 5-fluoro-2'-deoxyuridine-5'-monophosphate, demonstrated a 20-fold variation in the level of this enzyme among the tumor lines. Titrations performed in the presence or absence of added methylenetetrahydrofolate gave the same values for enzyme content. The cytotoxicity of 5-fluorodeoxyuridine to these cell lines (expressed as EC50 values) varied from 0.44 nM for SW 403 cells to 16 nM for HuTu 80 cells, and in all cases was reversed by the addition of thymidine. The concentration of 5-fluorodeoxyuridine required for cytotoxicity correlated directly (r = 0.98) with the level of thymidylate synthetase in the particular cell line. An inverse correlation (r = -0.95) was observed between the concentration of methotrexate producing cytotoxicity in these cell lines and their thymidylate synthetase levels. The cells were found to contain similar levels of dihydrofolate reductase and to possess normal transport capability for methotrexate.
...
PMID:Thymidylate synthetase levels as a factor in 5-fluorodeoxyuridine and methotrexate cytotoxicity in gastrointestinal tumor cells. 621 45


<< Previous 1 2 3 4 5 6 7 8 9 10 Next >>

---