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)

Four cultured mammalian cell lines, differing in intrinsic resistance to methotrexate over a 70-fold range, have been compared with respect to several biochemical factors that might influence response to the drug. Cellular activity of the enzymes dihydrofolate reductase and thymidylate synthetase and the total levels of folate cofactors did not vary by more than a factor of 2 among the cell lines. All the cell types were able to transport extracellular methotrexate efficiently across the cell membrane, and at comparable rates. A kinetic study of highly purified dihydrofolate reductases from the four sources revealed small differences in the Km values for dihydrofolate and reduced nicotinamide adenine dinucleotide phosphate. A study was made of the inhibition of the four dihydrofolate reductases by methotrexate, and Ki values were obtained by fitting the Zone B equation of Goldstein (Goldstein, A., J. Gen. Physiol., 27: 529-580, 1944) to the resulting data. Values Ki determined by this method correlated with intrinsic resistance of the cell lines and showed a 25-fold range from the most sensitive to the most resistant line. It is concluded that the response of a cell to methotrexate is significantly influenced by the dissociation constant of its dihydrofolate reductase-methotrexate complex.
...
PMID:Intrinsic resistance to methotrexate of cultured mammalian cells in relation to the inhibition kinetics of their dihydrololate reductases. 0 89

Pediococcus cerevisiae/AMr, resistant to amethopterin, possesses a higher dihydrofolate reductase (5, 6, 7, 8-tetrahydrofolate: NADP+ oxidoreductase, EC 1.5.1.3) activity than the parent, a folate-permeable and thus amethopterin-susceptible strain and than the wild-type. The properties of dihydrofolate reductase from the three strains have been compared. Temperature, pH optima, heat stability, as well amethopterin binding did not reveal significant differences between the enzymes from the susceptible and resistant strains. The enzyme from the wild-type was 10 times more sensitive to inhibition by amethopterin and more susceptible to heat denaturation. The apparent Km values for dihydrofolate in enzymes from the three strains were in the range of 4.8--7.2 muM and for NADPH 6.5--8.0 muM. The amethopterin-resistant strain exhibited cross-resistance to trimethoprim and was about 40-fold more resistant to the latter than the sensitive parent and the wild-type. The resistance to trimethoprim appears to be a direct result of the increased dihydrofolate reductase activity. Inhibition of dihydrofolate reductase activity by this drug was similar in the three strains. 10--20 nmol caused 50% inhibition of 0.02 enzyme unit. Trimethoprim was about 10 000 times less effective inhibitor of dihydrofolate reductase than amethopterin. The cell extract of the AMr strain possessed a folate reductase activity three times higher than that of the sensitive strain. The activities of other folate-related enzymes like thymidylate synthetase and 10-formyltetrahydrofolate synthetase (formate: tetrahydrofolate ligase (ADP-forming), EC 6.3.4.3) were similar in the three strains studied.
...
PMID:Resistance of Pediococcus cerevisiae to amethopterin as a consequence of changes in enzymatic activity and cell permeability. I. Dihydrofolate reductase, thymidylate synthetase and formyltetrahydrofolate synthetase in amethopterin-resistant and -sensitive strains of Pediococcus cerevisiae. 0 54

Megaloblastic anaemia is due to a derangement of DNA synthesis caused by insufficient supply of one or other of the four deoxyribonucleoside triphosphate (dNTP) precursors of DNA synthesis or by direct inhibition of one or other DNA polymerase. Reduced supply of the pyrimidine deoxythymidine triphosphate (dTTP) may be caused by folate or vitamin B12 deficiencies or by the action of dihydrofolate reductase inhibitors (e.g. methotrexate, pyrimethamine or trimethoprim), all of which cause reduced supply of the coenzyme 5, 10 methylene tetrahydrofolate (pentaglutamate) needed for thymidylate synthetase. Reduced dTTP supply may also be caused by direct inhibition of thymidylate synthetase by 5-fluorouracil. Reduced supply of both purines, deoxyadenosine triphosphate (dATP) and deoxyguanosine triphosphate (dGTP), may be caused by hydroxyurea, 6-mercaptopurine (and probably by another purine antagonist azaserine), whilst reduced supply of both pyrimidine DNA precursors, dTTP and dCTP (deoxycytidine triphosphate) may be due to inherited orotic aciduria or to treatment with azauridine. Cytosine arabinoside directly inhibits DNA polymerase. DNA replication is a discontinuous process and a number of enzymes are concerned with different aspects of the process. The parental strands partly unwind and a large number of initiation points or origins are activated on both strands. A primer RNA is first synthesised using the parental strand of DNA as template. Fragments of new DNA are then synthesised on the parental DNA template, starting at the RNA primer, under the action of one or other DNA polymerase (probably gamma). The RNA primer is then removed and the gap left is filled by further DNA synthesis under the action of a different DNA polymerase (probably alpha). The fragments of new DNA are joined to give newly synthesised stretches of DNA (replicons) which are then liigated together to form bulk DNA of enormous molecular weight. It is suggested here that reduced supply of one or other of the four deoxyribonucleoside triphosphate (dNTP) during the 'S' phase of the cell cycle (due to vitamin B12 or folate deficiency, drug treatment or other congenital or acquired abnormality in synthesis of the dNTP) impairs the cell's ability to elongate newly initiated DNA fragments by preventing gap-filling, the polymerase needed for gap-filling requiring substantially greater concentrations of the deoxyribonucleoside triphosphates than the polymerase involved in chain initiation. Cytosine arabinoside, which also may cause megaloblastosis, may affect principally the synthesis of new DNA fragments. Since active protein synthesis is needed for the cell to enter the S phase and RNA synthesis is needed to prime new DNA synthesis, megaloblastic anaemia may be expected to occur only when DNA synthesis is inhibited but protein and RNA synthesis are relatively unimpaired...
...
PMID:Vitamin B12--folate interrelations. 1 Jan 22

Methotrexate analogues, in which an additional nitrogen atom is inserted between the phenyl ring and the carbonyl group of the side chain, were prepared by photochemical methods. The compounds were less inhibitory toward dihydrofolate reductase and thymidylate synthetase derived from Lactobacillus casei than was methotrexate. They were also less cytotoxic against human lymphoblastic leukemia cells (CCRF-CEM). In vivo against L-1210 leukemia in mice, the aza homologue of methotrexate showed significant antitumor activity (%ILS = 55%) compared to methotrexate (%ILS = 88%).
...
PMID:Methotrexate analogues. 12. Synthesis and biological properties of some aza homologues. 10 16

Folic acid analogues containing an additional nitrogen atom between the phenyl ring and the carbonyl group of the side chain were synthesized. None of the compounds showed significant inhibitory activity against human lymphoblastic leukemia cells (CCRF-CEM) in culture or against Lactobacillus casei (ATCC 7469) growth. Against L1210 leukemia in mice, the aza homologue of folic acid, 4, and the aspartic acid analogue, 14, showed no increase in life span over control animals. These compounds were more toxic in vivo than the corresponding methotrexate analogues. Compound 4 supported the growth of Streptococcus faecium (ATCC 8043), and its tetrahydro derivative supported the growth of Pediococcus cerevisiae (ATCC 8081). These results strongly suggest that 4 can substitute for folate derivatives as cofactors for serine transhydroxymethylase, thymidylate synthetase, and dihydrofolate reductase.
...
PMID:Synthesis of aza homologues of folic acid. 10 17

Quantitative structure-activity relationships (QSAR) have been established for the inhibition of dihydrofolate reductase and thymidylate synthetase by 2,4-diaminoquinazoline-glutamic acid analogues. For dihydrofolate reductase from both human acute lymphocytic leukemia cells and murine L1210R cells, QSAR's obtained with 50 quinazolines were similar. On the other hand, for the inhibition of thymidylate synthetase from murine L1210S cells and from Lactobacillus casei, QSAR's formulated on the basis of data measured with 33 compounds were different, indicating that the two enzymes are dissimilar. The use of multivariate statistics including cluster analysis, factor analysis, and discriminant analysis is shown to facilitate the formulation of a satisfactory correlation equation. The procedure is demonstrated by the development of QSAR for the inhibition of thymidylate synthetase.
...
PMID:Multivariate analysis and quantitative structure-activity relationships. Inhibition of dihydrofolate reductase and thymidylate synthetase by quinazolines. 11 Sep 30

Resistance to antifolates in Bacillus subtilis strains results from the presence of an antifolate resistance mutation (afo). Strains which are thyA(+)afo are unconditionally resistant to antifolates. The conditional resistance of thyA afo strains is hypothesized to be due to the thyB(+) gene product (thymidylate synthetase B) having a high K(m) for the folate substrate, thus leading to thymineless death in the presence of antifolates. An alternative model for conditional antifolate resistance was shown to be incorrect by analysis of folate metabolism in methotrexate-treated cells. Genetic analysis and studies of the response of afo(+) cells to methotrexate suggested that most, if not all, B. subtilis thymine-requiring mutants are afo. Analysis of dihydrofolate reductase from afo cells did not reveal an obvious mechanism for antifolate resistance in those cells.
...
PMID:Conditional antifolate resistance in Bacillus subtilis thyA. 11 14

Methotrexate (MTX) inhibition of the growth of mouse or human leukemia cells in culture was partially prevented by either thymidine (dThd) or hypoxanthine. 5-Fluoro-2'-deoxyuridine (FdUrd) also decreased the growth-inhibitory potency of MTX in the presence of small concentrations of 5-formyltetrahydrofolate (citrovorum factor) and sufficient exogenous dThd to support the synthesis of thymidylate nucleotides by salvage mechanisms. In addition, citrovorum factor-induced reversal of MTX was several orders of magnitude more efficient in the presence of both FdUrd and dThd than in the presence of dThd alone or in the absence of both nucleosides. Likewise, the presence of FdUrd (3 microM) and dThd (5.6 microM) completely prevented the lethality of 0.3 mM MTX to L1210 cells in culture medium supplemented with micromolar concentrations of citrovorum factor. We propose that this protection against the cytotoxic effects of MTX by dThd, hypoxanthine, and FdUrd have a common biochemical mechanism--namely, inhibition of the de novo synthesis of thymidylate by either a direct [FdUrd; inhibition of thymidylate synthetase (thymidylate synthase; 5,10-methylenetetrahydrofolate:dUMP C-methyl-transferase, EC 2.1.1.45)] or indirect (dThd and hypoxanthine; feedback inhibition by anabolites on ribonucleotide reductase and deoxycytidylate deaminase) effect. The resultant decreased rate of loss of reduced folates due to de novo thymidylate synthesis would allow a higher degree of inhibition of dihydrofolate reductase to be endured without damage to the cell.
...
PMID:Role of thymidylate synthetase activity in development of methotrexate cytotoxicity. 16 May 58

Thymidilate synthetase (methylenetetrahydrofolate:dUMP C-methyltransferase) in crude extract from Diplococcus pneumoniae exhibits a partial but variable requirement for Mg-2+ depending upon the buffer. Optimum Mg-2+ concentration is between 0.014 and 0.02 M. The optimum pH for activity in a variety of buffers occurred as a broad peak between 7.0 and 7.7. In Tris/acetate buffer, but not in potassium phosphate buffer, the pH optimum was different in the presence and absence of Mg-2+. Methylation of uridylate, cytidylate and deoxycytidylate could not be demonstrated over a pH range of 5.0-8.0. The enzyme exhibited an apparent Km for deoxyuridylate of 3.08 - 10-5 M and an apparent Km for L-(+)(minus)-5,10-methylene tetrahydrofolate of 2.66 - 10-4 M. During molecular-sieve chromatography and sucrose density-gradient centrifugation, the enzyme was detectable only as a single catalytically active form of Mr 34 000-38 000. 2,4-Diamino quinazoline antifolates were better competitive inhibitors (Ki = 3-8 -10-6 M) of thymidylate synthetase than 2,4-diamino pteridines (Ki = 3- 10-5 M). 2-Amino-4-hydroxy-quinazolines were the best inhibitors (Ki = 1.3-2.9 - 10-6 M). All of the 2,4-diamino quinazolines and pteridines inhibited dihydrofolate reductase from D. pneumoniae in a nearly stoichiometric fashion (Ki = less than 10-10 M). The 2-amino-4-hydroxy-quinazolines were poor inhibitors of this enzyme (Ki = 10=5 M).
...
PMID:Thymidylate synthetase from Diplococcus pneumoniae, properties and inhibition by folate analogs. 23 97

Previous studies had suggested that methotrexate (MTX) may have actions other than inhibition of dihydrofolic acid reductase. In this study MTX was added to the assay incubation mixture of the enzyme thymidylate synthetase. 5-fluorodeoxyuridine (FUdR) or folinic acid was added separately as controls. The three compounds inhibited thymidylate synthetase with MTX achieving the maximal inhibition. It is suggested that MTX could exert its antineoplastic effect through this mechanism especially if malignant cells have little or no activity of dihydrofolic acid reductase.
...
PMID:Inhibition of thymidylate synthetase of the human lymphocytes. 31 99


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

---