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:2.7.7.7 (DNA polymerase)
17,007 document(s) hit in 31,850,051 MEDLINE articles (0.00 seconds)

The dose-response relationship between extracellular concentration of cytosine arabinoside (ara-C) and intracellular formation of the putative active metabolites of ara-C [ara-C incorporation into DNA and intracellular pools of ara-C in triphosphate form (ara-CTP)] was investigated in blast cells obtained from patients with acute nonlymphocytic leukemia (ANLL) by exposing these cells in vitro to 10, 100, or 1,000 nmol/L of ara-C. We studied 23 untreated patients who subsequently achieved complete remission (CR) with a regimen using daunorubicin and conventional doses of ara-C (ara-C-sensitive group), and 30 patients judged to be ara-C-resistant either by failing initial induction therapy (16 patients) or by having relapsed on an ara-C-containing maintenance regimen (14 patients). In both patient groups, ara-C incorporation into DNA and intracellular ara-CTP both displayed statistically significant increases in response to increasing extracellular concentrations of ara-C (P = .0001 in both cases), with the rate of increase of ara-CTP greater than that of ara-C incorporation. Moreover, blast cells from all patients, even those who were most clinically resistant to ara-C, were able to form ara-CTP and to incorporate ara-C into DNA. Each tenfold increment in extracellular ara-C concentration caused an 8.5-fold increase in ara-CTP, but only a 3.6-fold increase in ara-C incorporation into DNA. Thus, the efficiency of incorporation of ara-C into DNA (defined as the ratio of ara-C incorporation to ara-CTP pools) decreased by 58% with each tenfold increment in the extracellular concentration of ara-C (P less than .0001), presumably as a result of the inhibitory effect of ara-CTP on DNA polymerase. Using an analysis of covariance, modest differences were found in the levels of the ara-C metabolite variables in the ara-C-sensitive group as compared with the resistant group. However, because there was considerable overlap in ara-C metabolite formation among the patient groups, it was not possible to predict clinical outcome by these in vitro assessments of ara-C metabolism.
...
PMID:Metabolism of ara-C by blast cells from patients with ANLL. 371 4

DNA primase (EC 2.7.7.6) produces an RNA oligomer of approximately 10 bases, which is required by DNA polymerase alpha (EC 2.7.7.7) for the initiation of DNA synthesis. We partially purified DNA primase from acute lymphocytic leukemia cells from patients using several chromatography columns. Poly(dT) and poly(dC), but not poly(dA) or poly(dG), were good templates for ribonucleoside triphosphate (rNTP)-dependent DNA synthesis (i.e., DNA primase activity), and they were used in the study of the effect of natural and arabinofuranosyl nucleoside triphosphates on DNA primase activity. The Km for GTP in the poly(dC) primase assay was approximately 175 microM. All noncomplementary natural rNTPs and deoxyribonucleoside triphosphates (dNTPs) inhibited poly(dC) primase activity to a similar extent (Ki values of ATP and CTP were 610 and 517 microM, respectively). 1-beta-D-Arabinofuranosylcytosine 5'-triphosphate (araCTP) and 9-beta-D-arabinofuranosyladenine 5'-triphosphate (araATP) were more potent inhibitors of poly(dC) primase activity than were CTP and ATP (Ki values were approximately 125 microM). araCTP, araATP, CTP, and ATP inhibited DNA primase activity in a manner competitive with GTP. The concentration required to inhibit poly(dC) DNA primase activity by 50% was determined for a number of arabinofuranosyl nucleoside triphosphate analogs, and the relative potency of inhibition of DNA primase activity was as follows: rNTP = dNTP = 5-aza-dCTP less than ara-5-azaCTP = araTTP = araATP = araCTP less than 2-fluoro-araATP = 2'-azido-2'-deoxy araCTP less than 2'-fluoro-araTTP = 2'-fluoro-5-iodo-araCTP = 2'-fluoro-5-methyl-araCTP. In the poly(dT) primase assay ATP did not follow classic Michaelis-Menten kinetics (ATP exhibited positive cooperativity with a Hill coefficient of 2.0). However, this assay was very sensitive to araCTP (apparent Ki of 25 microM). In summary, these experiments suggested that DNA primase is controlled by the levels of ribonucleoside triphosphates, and that the perturbation of these pools by any agent could lead to the inhibition of DNA primase and thereby inhibit DNA synthesis. Furthermore, aranucleoside triphosphate analogs directly inhibited DNA primase, and it is possible that this effect may contribute to the cytotoxicity of these compounds.
...
PMID:Inhibition of DNA primase by nucleoside triphosphates and their arabinofuranosyl analogs. 380 92

Ribonucleoside and deoxyribonucleoside triphosphate pools have been measured in Escherichia coli infected with bacteriophage T4 DNA polymerase mutator, wild type, and antimutator alleles during mutagenesis by the base analogue 2-aminopurine. ATP and GTP pools expand significantly during mutagenesis, while CTP and UTP pools contract slightly. The DNA polymerase (gene 43) alleles and an rII lesion perturb normal dNTP pools more than does the presence of 2-aminopurine. We find no evidence that 2-aminopurine induces mutations indirectly by causing an imbalance in normal dNTP pools. Rather, it seems likely that, by forming base mispairs with thymine and with cytosine, 2-aminopurine is involved directly in causing bidirectional A.T in equilibrium G.C transitions. The ratios for 2-aminopurine deoxyribonucleoside triphosphate/dATP pools are 5-8% for tsL56 mutator and 1-5% for tsL141 antimutator and 43+ alleles. We conclude that the significant differences observed in the frequencies of induced transition mutations in the three alleles can be attributed primarily to the properties of the DNA polymerases with their associated 3'-exonuclease activities in controlling the frequency of 2-aminopurine.cystosine base mispairs.
...
PMID:Ribonucleoside and deoxyribonucleoside triphosphate pools during 2-aminopurine mutagenesis in T4 mutator-, wild type-, and antimutator-infected Escherichia coli. 388 83

Synergistic cell killing of human lymphoblastic leukemia cell line, CCRF-CEM, occurred when hydroxyurea (HU) was administered before 1-beta-D-arabinofuranosylcytosine (ara-C). At the optimal dose of HU (1mM), the ara-CTP concentration increased 4-fold and the intracellular accumulation of ara-C increased 4-fold, while the dCTP concentration decreased by more than 50%. Increased intracellular accumulation of ara-C after HU treatment was also observed in human acute myelogenous leukemic cells in circulating blood. Therefore, the synergistic cell kill of HU and ara-C may be the consequence of greater inhibition of DNA polymerase by the increased level of ara-CTP in the presence of the decreased concentration of the natural substrate of this enzyme, dCTP. This synergism was not due to an increased incorporation of ara-C into DNA since the treatment of cells with HU did not enhance the ara-C incorporation into DNA but rather suppressed it.
...
PMID:Mechanism of synergistic cell killing by hydroxyurea and cytosine arabinoside. 393 Apr 50

Isolation and characterization of Chinese hamster ovary cell mutants resistant to different DNA polymerase inhibitors (aphidicolin, ara-A and ara-C) have been described. A particular mutant (JK3-1-2A) characterized in detail was found to grow and synthesize DNA in medium containing an amount of aphidicolin tenfold greater than that which completely inhibited the growth and the DNA synthesis of the wild-type cells. An almost twofold increase in the specific activity of the DNA polymerase alpha was seen in this mutant. The mutant DNA polymerase showed altered aphidicolin inhibition kinetics of dCMP incorporation; the apparent Km for dCTP and the apparent Ki for aphidicolin were increased in the mutant. These alterations in the kinetic parameters were, however, abolished upon further purification of the enzyme. Ara-CTP was found to act as a competitive inhibitor of the dCMP incorporation by both the wild type and mutant enzymes. In contrast, the effect of aphidicolin on dCMP incorporation was either competitive (wild-type enzymes) or noncompetitive (mutant enzyme). The data presented showed that the sites of action for aphidicolin and ara-CTP were distinct; likewise the dCTP binding site appeared to be separate from other dNTP(s) binding sites. The drug resistance of the mutant was inherited as a dominant trait.
...
PMID:Chinese hamster ovary cell mutants resistant to DNA polymerase inhibitors. I. Isolation and biochemical genetic characterization. 393 Sep 21

A simple acetoxymercuration reaction for introducing covalently bound mercury atoms into nucleotides is described. The 5-mercuriacetate derivatives of UTP, CTP, dUTP, and dCTP, as well as the 7-mercuriacetate derivative of 7-deazaATP, have been prepared by this procedure and tested as substrates for nucleic acid polymerases. These nucleotides, in the absence of added mercaptan, are not polymerized and in most instances are potent enzyme inhibitors. However, conversion of these mercuriacetates to mercurithio compounds in situ by the addition of one of various mercaptans, yields nucleoside triphosphates that are excellent substrates for all polymerases tested: Escherichia coli and T7 RNA polymerases, DNA polymerase I of E. coli, DNA polymerase of avian myeloblastosis virus, and calf-thymus terminal deoxynucleotidyl transferase. By varying the mercaptan used to promote syntheses it is possible to access certain structural limitations in the enzyme's nucleoside triphosphate binding site. These mercurinucleotides appear to have a diversity of potential applications: (1) as heavy-atom reagents for crystallographic and microscopic studies; (2) as affinity probes for enzymes sensitive to sulfhydryl modification; (3) as steric probes of substrate-binding sites on enzymes; and (4) as reagents for forming covalent protein-polynucleotide complexes.
...
PMID:The synthesis and enzymatic polymerization of nucleotides containing mercury: potential tools for nucleic acid sequencing and structural analysis. 436 67

varphiX174 and M13 (fd) single-stranded circular DNAs are converted to their replicative forms by extracts of E. coli pol A1 cells. We find that the varphiX174 DNA-dependent reaction requires Mg(++), ATP, and all four deoxynucleoside triphosphates, but not CTP, UTP, or GTP. This reaction also involves the products of the dnaC, dnaD, dnaE (DNA polymerase III), and dnaG genes, but not that of dnaF (ribonucleotide reductase). The in vitro conversion of fd single-stranded DNA to the replicative form requires all four ribonucleoside triphosphates, Mg(++), and all four deoxynucleoside triphosphates. The reaction involves the product of gene dnaE but not those of genes dnaC, dnaD, dnaF, or dnaG. The reaction with fd DNA is inhibited by rifampicin or antibody to RNA polymerase, while the reaction with varphiX174 DNA is not affected by either. With the varphiX174 DNA-dependent reaction, activities have been detected that specifically complement extracts of dnaA, dnaB, dnaC, dnaD, or dnaG mutants.
...
PMID:Conversion of phiX174 and fd single-stranded DNA to replicative forms in extracts of Escherichia coli. 456 9

The properties of a nuclear preparation from rat liver and thymus are described. (1) Nearest-neighbour analysis after incorporation of (32)P-labelled nucleotide residues from dATP, dCTP, dGTP, dTTP and arabinofuranosyl analogues of CTP and ATP shows template-dependent DNA synthesis. (2) Where primer termini are limiting, incorporation of arabinofuranosyl analogues of AMP and CMP residues proceeds to a limit indicating that both of these analogues are DNA chain terminators. (3) No large differences have been found between the priming potentialities or the intrinsic DNA polymerase activities of nuclei from resting or regenerating liver and the relationship of this DNA synthesis in vitro to DNA replication or repair in vivo is briefly discussed.
...
PMID:Deoxyribonucleic acid synthesis in mammalian nuclei. Incorporation of deoxyribonucleotides and chain-terminating nucleotide analogues. 511 93

9-beta-D-Arabinofuranosyladenine (ara-A), 1-beta-D-arabinofuranosylcytosine (ara-C), and their 5'-triphosphates (ara-ATP and ara-CTP) were tested for ability to inhibit the hepatitis B virus (HBV)-associated deoxyribonucleic acid (DNA) polymerase. Ara-C did not inhibit the HBV DNA polymerase at the concentrations tested, ara-A did so by 50% at a concentration of 30 mM, with the inhibition noncompetitive with respect to deoxyadenosine 5-triphosphate (dATP). Ara-ATP and ara-CTP inhibited the DNA polymerase test competitively with respect to dATP and dCTP, respectively. Both compounds were also active after initiation of the DNA polymerase reaction. The inhibition caused by ara-ATP and ara-CTP was shown to be reversible, with no evidence that ara-ATP or ara-CTP was incorporated into the HBV DNA.
...
PMID:Inhibition of hepatitis B virus deoxyribonucleic acid polymerase by the 5'-triphosphates of 9-beta-D-arabinofuranosyladenine and 1-beta-D-arabinofuranosylcytosine. 616 46

Ara-C should be converted to ara-CTP to inhibit DNA polymerase in the malignant cells but is rapidly inactivated to uracil arabinoside (ara-U) by cytidine deaminase in human tissue. Therefore, production as well as maintenance of ara-CTP in the cells is a function of both phosphorylation and deamination of ara-C, but is more dependent on the latter, because the deamination is several times superior to the former in terms of enzymatic activities. In chemotherapy with ara-C, the rate of the inactivation should be estimated for evaluating antitumor effect of the agent. Determination of serum or plasma deaminase activity can be a useful parameter of the inactivation. Attempts have been made to enhance the antitumor activity of ara-C by preventing deamination and a number of ara-C derivatives resistant to the deamination such as cyclocytidine, ara-C-5'-ester and acyl ara-C have been introduced. Cyclo-C gradually receives non-enzymatic hydrolysis to produce ara-C in neutral medium, which is useful for maintaining plasma ara-C level. Acyl ara-C such as behenoyl-ara-C (BHAC) is well incorporated into the cells and is highly distributed to lipophilic components such as membrane, microsome and mitochondria in the cells. The extremely gradual conversion of BHAC to ara-C in the cells is considered to be useful for maintaining effective intracellular concentration. A part of BHAC could be phosphorylated before deacylation. After intravenous administration of BHAC, the plasma drug concentrations are maintained significantly longer than those after the administration of the equivalent dose of ara-C. Therefore, BHAC is more resistant to the deamination than cyclo-C and the antitumor effect of the former is suspected to be milder but prolonged than that of ara-C or cyclo-C.
...
PMID:[Chemotherapy of the malignancies from the viewpoint of pharmacology and biochemistry of cytosine arabinoside (ara-C) and its derivatives]. 619 11


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

---