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)

5,10-Dideazatetrahydrofolate (DDATHF) is a new antimetabolite designed as an inhibitor of folate metabolism at sites other than dihydrofolate reductase. DDATHF was found to inhibit the growth of L1210 and CCRF-CEM cells in culture at concentrations in the range of 10-30 nM. The inhibitory effect of DDATHF on the growth of L1210 and CCRF-CEM cells was reversed by either hypoxanthine or aminoimidazole carboxamide. Growth inhibition by DDATHF was prevented by addition of both thymidine and hypoxanthine, but not by thymidine alone. 5-Formyltetrahydrofolate reversed the effects of DDATHF in a dose-dependent manner. DDATHF had no appreciable inhibitory activity against either dihydrofolate reductase or thymidylate synthase in vitro, but was found to be an excellent substrate for folylpolyglutamate synthetase. DDATHF had little or no effect on incorporation of either deoxyuridine or thymidine into DNA, in distinct contrast to the effects of the classical dihydrofolate reductase inhibitor, methotrexate. DDATHF was found to deplete cellular ATP and GTP over the same concentrations as those inhibitory to leukemic cell growth, suggesting that the locus of DDATHF action was in the de novo purine biosynthesis pathway. The synthesis of formylglycinamide ribonucleotide in intact L1210 cells was inhibited by DDATHF with the same concentration dependence as inhibition of growth. This suggested that DDATHF inhibited glycinamide ribonucleotide transformylase, the first folate-dependent enzyme of de novo purine synthesis. DDATHF is a potent folate analog which suppresses purine synthesis through direct or indirect inhibition of glycinamide ribonucleotide transformylase.
...
PMID:A new folate antimetabolite, 5,10-dideaza-5,6,7,8-tetrahydrofolate is a potent inhibitor of de novo purine synthesis. 290 24

We have investigated the energy requirement of mitochondrial protein import with a simplified system containing only isolated yeast mitochondria, energy sources and a purified precursor protein. This precursor was a fusion protein composed of 22 residues of the cytochrome oxidase subunit IV pre-sequence fused to mouse dihydrofolate reductase. Import of this protein required not only an energized inner membrane, but also ATP. ATP could be replaced by GTP, but not by CTP, TTP or non-hydrolyzable ATP analogs. Added ATP did not increase the membrane potential of respiring mitochondria; it supported import even if the proton-translocating mitochondrial ATPase and the entry of ATP into the matrix were blocked. We conclude that ATP exerts its effect on mitochondrial protein import outside the inner membrane.
...
PMID:Both ATP and an energized inner membrane are required to import a purified precursor protein into mitochondria. 303 90

The variations with pH of the kinetic parameters and primary deuterium isotope effects for the reaction of NADPH with dihydrofolate reductase from Escherichia coli have been determined. The aims of the investigations were to elucidate the chemical mechanism of the reaction and to obtain information about the location of the rate-limiting steps. The V and V/KNADPH profiles indicate that a single ionizing group at the active center of the enzyme must be protonated for catalysis, whereas the Ki profiles show that the binding of NADPH to the free enzyme and of ATP-ribose to the enzyme-dihydrofolate complex is pH independent. From the results of deuterium isotope effects on V/KNADPH, it is concluded that NADPH behaves as a sticky substrate. It is this stickiness that raises artificially the intrinsic pK value of 6.4 for the Asp-27 residue of the enzyme-dihydrofolate complex [Howell, E. E., Villafranca, J. E., Warren, M. S., Oatley, S. J., & Kraut, J. (1986) Science (Washington, D.C.) 231, 1123] to an observed value of 8.9. Thus, the binary enzyme complex is largely protonated at neutral pH. The elevation of the intrinsic pK value of 6.4 for the ternary enzyme-NADPH-dihydrofolate complex to 8.5 is not due to the kinetic effects of substrates. Rather, it is the consequence of the lower, pH-independent rate of product release and the faster pH-dependent catalytic step. At neutral pH, the proportion of enzyme present as a protonated ternary enzyme-substrate complex is sufficient to keep catalysis faster than product release.(ABSTRACT TRUNCATED AT 250 WORDS)
...
PMID:Mechanism of the reaction catalyzed by dihydrofolate reductase from Escherichia coli: pH and deuterium isotope effects with NADPH as the variable substrate. 305 78

Folic acid metabolism in eukaryotic cells consists of a network of enzymatic reactions in which 1-carbon (C1) units at three different oxidation states are 1) interconverted while linked to the 5- and/or 10-positions of tetrahydrofolate, or 2) added to, or taken from, tetrahydrofolate. Particularly important in the latter category are reactions involving C1-tetrahydrofolate adducts in the synthesis of inosinate, thymidylate, serine, and methionine. Tetrahydrofolate, a central component of the network, can be generated from: 1) folate, via the NADPH-dependent dihydrofolate reductase; 2) 5-methyltetrahydrofolate via the methyl B12-dependent methionine synthetase; or 3) 5-formyltetrahydrofolate via a sequence of reactions beginning with the ATP-dependent isomerization to 5,10-methenyltetrahydrofolate or via transfer of the formyl group to glutamate. Because of the close relationship of folic acid metabolism to cell replication, folate-dependent enzymes provide excellent targets for cancer chemotherapy. This potential has not yet been realized, however, except for dihydrofolate reductase and thymidylate synthetase, which are strongly inhibited by the anti-cancer agents methotrexate (MTX) and FUra. The following enzymes are particularly attractive as targets for future exploitation in chemotherapy: 1) the two transformylases involved in purine nucleotide synthesis, 2) serine hydroxymethyltransferase, 3) methionine synthetase, and 4) methylenetetrahydrofolate dehydrogenase. Suggestions are also made for the development of new agents based upon a strategy of enzyme-targeted chemotherapy.
...
PMID:Folic acid metabolism and its disruption by pharmacologic agents. 312 3

Glutathione synthetase from Escherichia coli B showed amino acid sequence homology with mammalian and bacterial dihydrofolate reductases over 40 residues, although these two enzymes are different in their reaction mechanisms and ligand requirements. The effects of ligands of dihydrofolate reductase on the reaction of E. coli B glutathione synthetase were examined to find resemblances in catalytic function to dihydrofolate reductase. The E. coli B enzyme was potently inhibited by 7,8-dihydrofolate, methotrexate, and trimethoprim. Methotrexate was studied in detail and proved to bind to an ATP binding site of the E. coli B enzyme with K1 value of 0.1 mM. The homologous portion of the amino acid sequence in dihydrofolate reductases, which corresponds to the portion coded by exon 3 of mammalian dihydrofolate reductase genes, provided a binding site of the adenosine diphosphate moiety of NADPH in the crystal structure of dihydrofolate reductase. These analyses would indicate that the homologous portion of the amino acid sequence of the E. coli B enzyme provides the ATP binding site. This report gives experimental evidence that amino acid sequences related by sequence homology conserve functional similarity even in enzymes which differ in their catalytic mechanisms.
...
PMID:Homology of Escherichia coli B glutathione synthetase with dihydrofolate reductase in amino acid sequence and substrate binding site. 355 73

The involvement of the nucleoside triphosphates in the initiation of the synthesis of the messenger ribonucleic acid of five T4 specific enzymes has been studied. Only one of these, the messenger RNA for deoxynucleosidemonophosphate kinase, can be initiated in the presence of one nucleoside triphosphate, namely ATP. All of the remaining four require the presence of at least two nucleoside triphosphates during the initiation period. The combination of ATP and UTP was best for the initiation of messenger RNA for dihydrofolate reductase, ATP and CTP for deoxycytidylate hydroxymethyltransferase and beta-glucosyltransferase, and ATP and GTP for alpha-glucosyltransferase. We have concluded that there is a great variation in the nucleotide composition and sequence of the initiation sites in T4 DNA. No correlation in the requirements of nucleoside triphosphates during the initiation period could be observed among the five systems studied according to their classification as one type or another of "early" T4 messenger RNA.
...
PMID:Initiation characteristics for the synthesis of five T4 phage-specific messenger RNAs in vitro. 436 Sep 43

The uptake of glycolate oxidase into peroxisomes has been studied using an in vitro import system. Import of glycolate oxidase was found to be ATP-dependent and temperature-dependent and specific for glyoxysomes. In these respects it resembles the import of isocitrate lyase into both glyoxysomes and leaf-type peroxisomes; thus the ATP-dependence and temperature dependence appear to be general properties of plant microbody protein import. Two mutant versions of glycolate oxidase were prepared lacking 59 amino acids of the N-terminus and 53 amino acids of C-terminus, respectively. Both were capable of ATP-dependent import, whereas a fusion protein consisting of the cytosolic protein dihydrofolate reductase linked to the last 20 amino acids of glycolate oxidase bound to glyoxysomes but did not enter the organelle.
...
PMID:Investigation of the energy requirement and targeting signal for the import of glycolate oxidase into glyoxysomes. 760 Oct 95

Two cDNA clones encoding distinct forms of plastid pyruvate kinase (designated Pka and Pkg) have recently been characterized. Pkg is found in both leucoplasts and chloroplasts, whereas Pka is present only in leucoplasts. The precursors of these proteins have different in vitro import characteristics. The Pkg precursor behaves like a typical stromal protein precusor with both types of plastid. In contrast, Pka precursors accumulate on the outer envelope membrane of leucoplasts under the same assay conditions and require a higher level of ATP for import into the organelle. Interestingly, the binding of Pka precursors to chloroplasts cannot be detected at any tested level of ATP even though the precursors are imported into the organelle at higher concentrations of ATP. Various N-terminal deletions and chimeric fusions were used to examine the translocation signaling mechanism of the Pka precursor. The N-terminal 83-amino-acid segment of Pka contains a transit peptide that is capable of directing dihydrofolate reductase and the mature body of Pkg into both types of plastid. Unlike the complete Pka precursor, these fusion proteins behave like typical stromal protein precursors. The behavior of the Pka transit peptide is influenced by a 19-amino-acid domain (-P-S-S-I-E-V-D-A-V-T-E-T-E-L-K-E-N-G-F-) located immediately downstream of the N-terminal 83-residue segment. Deletion of this domain from Pka alters its import properties such that it resembles a typical stromal protein precursor. Re-introduction of the 19-residue domain into the Dhfr fusion protein alters its import characteristics to resemble that of the complete Pka precursor. This 19-amino-acid domain can also influence the function of transit sequences from other precursors when it is placed immediately behind the transit peptide. These results suggest that this 19-amino-acid domain plays an important role in governing the import characteristics of the Pka precursor. We have named this 19-residue segment the "import modifying domain."
...
PMID:Import characteristics of a leucoplast pyruvate kinase are influenced by a 19-amino-acid domain within the protein. 762 84

In an attempt to understand the mechanisms of sorting of mitochondrial inner membrane proteins, we have analyzed the import of subunit 9 of the mitochondrial F1F0-ATPase (Su9) from Neurospora crassa, an integral inner membrane protein. A chimeric protein was used consisting of the presequence and the first transmembrane domain of Su9 fused to mouse dihydrofolate reductase (preSu9(1-112)-DHFR). This protein attains the correct topology across the inner membrane (Nout-Cin) following import. The transmembrane domain becomes first completely imported into the matrix, where after processing of the presequence, it mediates membrane insertion and export of the N-terminal tail. Import and export steps can be experimentally dissected into two distinct events. Translocation of the N-terminal hydrophilic tail out of the matrix was blocked when the presequence was not processed, indicating an important role of the sequences and charges flanking the hydrophobic domain. Furthermore, export was supported by a delta pH and required matrix ATP hydrolysis. Thus the hydrophobic transmembrane domain operates as a membrane insertion signal and not as a stop-transfer signal. Our findings suggest that several aspects of this sorting process have been conserved from their prokaryotic ancestors.
...
PMID:Conservative sorting of F0-ATPase subunit 9: export from matrix requires delta pH across inner membrane and matrix ATP. 762 45

The N-end rule relates the in vivo half-life of a protein to the identity of its N-terminal residue. In eukaryotes, the N-end rule pathway is a ubiquitin-dependent, proteasome-based system that targets and processively degrades proteins bearing certain N-terminal residues. Arg-DHFR, a modified dihydrofolate reductase bearing an N-terminal arginine (destabilizing residue in the N-end rule), is short lived in ATP-supplemented reticulocyte extract. It is shown here that methotrexate, which is a folic acid analog and high affinity ligand of DHFR, inhibits the degradation but not ubiquitination of Arg-DHFR by the N-end rule pathway. The degradation of other N-end rule substrates is not affected by methotrexate. We discuss implications of these results for the mechanism of proteasome-mediated protein degradation.
...
PMID:Methotrexate inhibits proteolysis of dihydrofolate reductase by the N-end rule pathway. 771 22


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

---