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)

The activities of glucose-6-phosphate dehydrogenase (D-glucose-6-phosphate: NADP oxidoreductase, G6PD), 6-phosphogluconate dehydrogenase (6-phospho-D-gluconate: NADP oxidoreductase, 6PGD), hexokinase (ATP: D-hexose 6-phosphotransferase, Hx), lactate dehydrogenase (D-lactate: NAD oxidoreductase, LDH). glutamate oxaloacetate transaminase (L-aspartate: 2 oxoglutarate aminotransferase, GOT) and dihydrofolate reductase (DHFR) were measured at 8 a.m. in leucocytes of healthy individuals and patients with chronic myeloid leukaemia (CML), chronic lymphatic leukaemia (CLL), myelofibrosis with myeloid metaplasia and polycythaemia vera. In view of the heterogeneity of the leucocyte populations in these conditions, the enzyme activities were correlated to the number of immature cells in CML and to the percentage of lymphocytes in CLL. No differences in the enzyme activities were found between the white cells of healthy individuals, myelofibrosis with myeloid metaplasia and polycythaemia vera. In CML the activities of all enzymes except GOT correlated directly with the number of immature cells; an inverse correlation with the number of lymphocytes was observed in CLL. GOT was the only enzyme whose activity correlated with the number of lymphocytes in the cell suspension. Furthermore, a significantly higher activity of this enzyme was found in Ficoll-isolated CLL lymphocytes as compared to normal lymphocytes.
...
PMID:Blood leucocyte enzymes. II. Activities at 8-9 a.m. in cells of normal subjects, chronic lymphatic leukaemia and chronic myeloid leukaemia patients. 105 70

1. Riboflavin deficiency at two levels of severity was produced in weanling rats by feeding deficient diets for 6 weeks and using neck collars to prevent coprophagy. The severity of deficiency was monitored by growth, liver flavin levels and the activation coefficient of erythrocyte glutathione oxidoreductase (NAD(P)H) (EC 1.6.4.2). Control groups, receiving the same diet with ample added riboflavin, were fed either ad lib., or were pair-fed with the deficient animals. 2. The hepatic flavoenzyme, methylenetetrahydrofolate reductase (NADPH) (EC 1.5.1.20), was very markedly affected by severe riboflavin deficiency and was significantly, but less markedly, affected by the intermediate level of deficiency. This reduction in activity was due primarily to the direct effect of the diminished supply of riboflavin, and occurred to only a small extent as a result of inanition, demonstrated by a moderate reduction in activity in the more severely food-restricted of the two pair-fed groups. Since the enzyme is assayed in the presence of its flavin cofactor, FAD, it clearly cannot be reactivated in vitro, as some other depleted flavoenzymes can. The discriminatory ability in distinguishing between severe and moderate riboflavin deficiency in vivo confers some potential advantages on this oxidoreductase as a possible index of riboflavin status. 3. The hepatic activity of another key folate-metabolizing enzyme, dihydrofolate reductase (EC 1.5.1.3), was not diminished by riboflavin deficiency in the present study. 4. The ratio, labelled 5-methyltetrahydrofolic acid:other labelled compounds derived from intraperitoneally injected pteroylglutamic acid in extracts of hepatic tissue was significantly reduced in the riboflavin-deficient groups, indicating the possibility of an effect of riboflavin deficiency on folate metabolism in vivo.
...
PMID:The effect of riboflavin deficiency on methylenetetrahydrofolate reductase (NADPH) (EC 1.5.1.20) and folate metabolism in the rat. 367 70

The biosynthesis of tetrahydrobiopterin from either dihydroneopterin triphosphate, sepiapterin, dihydrosepiapterin or dihydrobiopterin was investigated using extracts from human liver, dihydrofolate reductase and purified sepiapterin reductase from human liver and rat erythrocytes. The incorporation of hydrogen in tetrahydrobiopterin was studied in either 2H2O or in H2O using unlabeled NAD(P)H or (R)-(4-2H)NAD(P)H or (S)-(4-2H)NAD(P)H. Dihydrofolate reductase catalyzed the transfer of the pro-R hydrogen of NAD(P)H during the reduction of 7,8-dihydrobiopterin to tetrahydrobiopterin. Sepiapterin reductase catalyzed the transfer of the pro-S hydrogen of NADPH during the reduction of sepiapterin to 7,8-dihydrobiopterin. In the presence of partially purified human liver extracts one hydrogen from the solvent is introduced at position C(6) and the 4-pro-S hydrogen from NADPH is incorporated at each of the C(1') and C(2') position of BH4. Label from the solvent is also introduced into position C(3'). These results suggest that dihydrofolate reductase is not involved in the biosynthesis of tetrahydrobiopterin from dihydroneopterin triphosphate. They are consistent with the assumption of the occurrence of a 6-pyruvoyl-tetrahydropterin intermediate, which is proposed to be formed upon triphosphate elimination from dihyroneopterin triphosphate, and via an intramolecular redox reaction. Our results suggest that the reduction of 6-pyruvoyl-tetrahydropterin might be catalyzed by sepiapterin reductase.
...
PMID:Tetrahydrobiopterin biosynthesis. Studies with specifically labeled (2H)NAD(P)H and 2H2O and of the enzymes involved. 388 18

We report the sequence of an 18,002 bp DNA fragment from the right arm of Saccharomyces cerevisiae chromosome XI. This segment contains nine complete open reading frames (ORFs), YKR401 to YKR409, and part of another ORF, YKR400, covering altogether 87.2% of the entire sequence. One of them, YKR400, encodes an NAD-dependent 5,10-methylene-tetrahydrofolate dehydrogenase. YKR404, YKR405 and YKR406 correspond to the previously characterized HBS1, MRP-L20 and PRP16 genes, coding for a translation elongation factor, a mitochondrial ribosomal protein and an ATP-binding protein, respectively. The putative product of YKR407 contains the zinc-binding region signature of neutral zinc metallopeptidases. The five other ORFs do not show significant homology to any known protein.
...
PMID:The complete sequence of an 18,002 bp segment of Saccharomyces cerevisiae chromosome XI contains the HBS1, MRP-L20 and PRP16 genes, and six new open reading frames. 820 64

We report here the Raman spectra of NADPH, NADP+, 3-acetylpyridine adenine dinucleotide (AcPdADP+), NADH and a fragment of these molecules, 2'-phospho-adenosine-5'-diphosphoribose (Ado2'p5'ppRib), bound to Escherichia coli dihydrofolate reductase (DHFR). The positions that are observed for the bound adenosine 'triplet' bands are consistent with a protein binding pocket for this group which is quite hydrophobic in nature. No binding effect is observed on Raman bands associated with the nicotinamide group of NADP+ as a binary complex with DHFR, suggesting very loose, if any, binding of this group. In contrast, changes in the Raman spectrum of the nicotinamide group of NADP+ bound to an inhibitor (trimethoprim) ternary complex of DHFR are clearly observed which indicate substantial binding interaction. The carboxamide group of bound NADPH (and NADH) adopts the trans conformation. A 35-cm-1 upshift is observed in the rocking motion of the carboxamide -NH2 group of NADPH, and a 5-cm-1 upward shift is seen in the C=O stretch mode of AcPdADP+ upon binding to the enzyme-trimethoprim complex. These results suggest that the -NH2 group of the carboxamide moiety is more tightly hydrogen bonded in the protein binding pocket than in solution while that of the C=O group is less tightly hydrogen bonded; these hydrogen bonds would appear to be responsible for holding the nicotinamide headgroup in place properly for catalysis. We have compared this with the results obtained previously in other protein complexes, and interpret the observed shifts in these bands as a measure of the hydrogen bonding enthalpy of the -NH2 and C=O groups with their protein environments. Perhaps surprisingly, the magnitude of the hydrogen bonding enthalpy takes on a limited number of discrete values over five protein complexes rather than over a continuous range. The effect that this has on the catalytic properties of DHFR and the other NAD dehydrogenases that we have studied to date, particularly their stereochemistry, is discussed. A small downward shift is observed for the P = O stretch of the 2'-phosphate moiety of NADP. This indicates that the 2'-phosphate moiety binds to DHFR in the dianionic form. Furthermore, the local enthalpic interaction that the 2'-phosphate group has with protein is stronger than its interaction with water.
...
PMID:A study of the binding of NADP coenzymes to dihydrofolate reductase by raman difference spectroscopy. 834 89

Pteridine reductase 1 (PTR1) is a novel broad spectrum enzyme of pterin and folate metabolism in the protozoan parasite Leishmania. Overexpression of PTR1 confers methotrexate resistance to these protozoa, arising from the enzyme's ability to reduce dihydrofolate and its relative insensitivity to methotrexate. The kinetic mechanism and stereochemical course for the catalyzed reaction confirm PTR1's membership within the short chain dehydrogenase/reductase (SDR) family. With folate as a substrate, PTR1 catalyzes two rounds of reduction, yielding 5,6,7, 8-tetrahydrofolate and oxidizing 2 equiv of NADPH. Dihydrofolate accumulates transiently during folate reduction and is both a substrate and an inhibitor of PTR1. PTR1 transfers the pro-S hydride of NADPH to carbon 6 on the si face of dihydrofolate, producing the same stereoisomer of THF as does dihydrofolate reductase. Product inhibition and isotope partitioning studies support an ordered ternary complex mechanism, with NADPH binding first and NADP+ dissociating after the reduced pteridine. Identical kinetic mechanisms and NAD(P)H hydride chirality preferences are seen with other SDRs. An observed tritium effect upon V/K for reduction of dihydrofolate arising from isotopic substitution of the transferred hydride was suppressed at a high concentration of dihydrofolate, consistent with a steady-state ordered kinetic mechanism. Interestingly, half of the binary enzyme-NADPH complex appears to be incapable of rapid turnover. Fluorescence quenching results also indicate the existence of a nonproductive binary enzyme-dihydrofolate complex. The nonproductive complexes observed between PTR1 and its substrates are unique among members of the SDR family and may provide leads for developing antileishmanial therapeutics.
...
PMID:Leishmania major pteridine reductase 1 belongs to the short chain dehydrogenase family: stereochemical and kinetic evidence. 952 31

The interaction of type II R67 dihydrofolate reductase (DHFR) with its cofactor nicotinamide adenine dinucleotide phosphate (NADP(+)) has been studied using nuclear magnetic resonance (NMR). Doubly labeled [U-(13)C,(15)N]DHFR was obtained from Escherichia coli grown on a medium containing [U-(13)C]-D-glucose and (15)NH(4)Cl, and the 16 disordered N-terminal amino acids were removed by treatment with chymotrypsin. Backbone and side chain NMR assignments were made using triple-resonance experiments. The degeneracy of the amide (1)H and (15)N shifts of the tetrameric DHFR was preserved upon addition of NADP(+), consistent with kinetic averaging among equivalent binding sites. Analysis of the more titration-sensitive DHFR amide resonances as a function of added NADP(+) gave a K(D) of 131 +/- 50 microM, consistent with previous determinations using other methodology. We have found that the (1)H spectrum of NADP(+) in the presence of the R67 DHFR changes as a function of time. Comparison with standard samples and mass spectrometric analysis indicates a slow conversion of NADP(+) to NAD(+), i.e., an apparent NADP(+) phosphatase activity. Studies of this activity in the presence of folate and a folate analogue support the conclusion that this activity results from an interaction with the DHFR rather than a contaminating phosphatase. (1)H NMR studies of a mixture of NADP(+) and NADPH in the presence of the enzyme reveal that a ternary complex forms in which the N-4A and N-4B nuclei of the NADPH are in the proximity of the N-4 and N-5 nuclei of NADP(+). Studies using the NADP(+) analogue acetylpyridine adenosine dinucleotide phosphate (APADP(+)) demonstrated a low level of enzyme-catalyzed hydride transfer from NADPH. Analysis of DHFR backbone dynamics revealed little change upon binding of NADP(+). These additional catalytic activities and dynamic behavior are in marked contrast to those of type I DHFR.
...
PMID:NMR studies of the interaction of a type II dihydrofolate reductase with pyridine nucleotides reveal unexpected phosphatase and reductase activity. 1450 65

During growth on one-carbon (C1) compounds, the aerobic alpha-proteobacterium Methylobacterium extorquens AM1 synthesizes the tetrahydromethanopterin (H4MPT) derivative dephospho-H4MPT as a C1 carrier in addition to tetrahydrofolate. The enzymes involved in dephospho-H4MPT biosynthesis have not been identified in bacteria. In archaea, the final step in the proposed pathway of H4MPT biosynthesis is the reduction of dihydromethanopterin (H2MPT) to H4MPT, a reaction analogous to the reaction of the bacterial dihydrofolate reductase. A gene encoding a dihydrofolate reductase homolog has previously been reported for M. extorquens and assigned as the putative H2MPT reductase gene (dmrA). In the present work, we describe the biochemical characterization of H2MPT reductase (DmrA), which is encoded by dmrA. The gene was expressed with a six-histidine tag in Escherichia coli, and the recombinant protein was purified by nickel affinity chromatography and gel filtration. Purified DmrA catalyzed the NAD(P)H-dependent reduction of H2MPT with a specific activity of 2.8 micromol of NADPH oxidized per min per mg of protein at 30 degrees C and pH 5.3. Dihydrofolate was not a substrate for DmrA at the physiological pH of 6.8. While the existence of an H2MPT reductase has been proposed previously, this is the first biochemical evidence for such an enzyme in any organism, including archaea. Curiously, no DmrA homologs have been identified in the genomes of known methanogenic archaea, suggesting that bacteria and archaea produce two evolutionarily distinct forms of dihydromethanopterin reductase. This may be a consequence of different electron donors, NAD(P)H versus reduced F420, used, respectively, in bacteria and methanogenic archaea.
...
PMID:Biochemical characterization of a dihydromethanopterin reductase involved in tetrahydromethanopterin biosynthesis in Methylobacterium extorquens AM1. 1502 91

Recent studies demonstrate that oxidative inactivation of tetrahydrobiopterin (H4B) may cause uncoupling of endothelial nitric oxide synthase (eNOS) to produce superoxide (O2*-). H4B was found recyclable from its oxidized form by dihydrofolate reductase (DHFR) in several cell types. Functionality of the endothelial DHFR, however, remains completely unknown. Here we present findings that specific inhibition of endothelial DHFR by RNA interference markedly reduced endothelial H4B and nitric oxide (NO.) bioavailability. Furthermore, angiotensin II (100 nmol/liter for 24 h) caused a H4B deficiency that was mediated by H2O2-dependent down-regulation of DHFR. This response was associated with a significant increase in endothelial O2*- production, which was abolished by eNOS inhibitor N-nitro-L-arginine-methyl ester or H2O2 scavenger polyethylene glycol-conjugated catalase, strongly suggesting H2O2-dependent eNOS uncoupling. Rapid and transient activation of endothelial NAD(P)H oxidases was responsible for the initial burst production of O2* (Rac1 inhibitor NSC 23766 but not an N-nitro-L-arginine-methyl ester-attenuated ESR O2*- signal at 30 min) in response to angiotensin II, preceding a second peak in O2*- production at 24 h that predominantly depended on uncoupled eNOS. Overexpression of DHFR restored NO. production and diminished eNOS production of O2*- in angiotensin II-stimulated cells. In conclusion, these data represent evidence that DHFR is critical for H4B and NO. bioavailability in the endothelium. Endothelial NAD(P)H oxidase-derived H2O2 down-regulates DHFR expression in response to angiotensin II, resulting in H4B deficiency and uncoupling of eNOS. This signaling cascade may represent a universal mechanism underlying eNOS dysfunction under pathophysiological conditions associated with oxidant stress.
...
PMID:Endothelial dihydrofolate reductase: critical for nitric oxide bioavailability and role in angiotensin II uncoupling of endothelial nitric oxide synthase. 1594 33

Isoniazid is a key drug used in the treatment of tuberculosis. Isoniazid is a pro-drug, which, after activation by the katG-encoded catalase peroxidase, reacts nonenzymatically with NAD(+) and NADP(+) to generate several isonicotinoyl adducts of these pyridine nucleotides. One of these, the acyclic 4S isomer of isoniazid-NAD, targets the inhA-encoded enoyl-ACP reductase, an enzyme essential for mycolic acid biosynthesis in Mycobacterium tuberculosis. Here we show that the acyclic 4R isomer of isoniazid-NADP inhibits the M. tuberculosis dihydrofolate reductase (DHFR), an enzyme essential for nucleic acid synthesis. This biologically relevant form of the isoniazid adduct is a subnanomolar bisubstrate inhibitor of M. tuberculosis DHFR. Expression of M. tuberculosis DHFR in Mycobacterium smegmatis mc(2)155 protects cells against growth inhibition by isoniazid by sequestering the drug. Thus, M. tuberculosis DHFR is the first new target for isoniazid identified in the last decade.
...
PMID:Mycobacterium tuberculosis dihydrofolate reductase is a target for isoniazid. 1664 61


1 2 3 Next >>

---