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:5.99.1.3 (topoisomerase)
9,911 document(s) hit in 31,850,051 MEDLINE articles (0.00 seconds)

The effect of poly(ADP-ribosylation) on calf thymus topoisomerase type II reactions has been investigated. Unknotting of phage P4 head DNA, and relaxation and catenation of supercoiled PM2 DNA are inhibited. We conclude that the inhibition results from poly(ADP-ribosylation) on the following grounds. Firstly, the enzyme poly(ADP-ribose) (PADPR) synthetase and NAD are required, secondly, the competitive synthetase inhibitor nicotinamide abolishes topoisomerase inhibition, and thirdly, the polymer alone is not inhibitory. The mechanism of inhibition appears to be disruption of the strand cleavage reaction. A topoisomerase-DNA complex can be formed that upon treatment with protein denaturant at low ionic strength results in strand cleavage. The amount of DNA present in such a cleavable-complex progressively decreased following pretreatment of topoisomerase type II with PADPR synthetase and increasing concentrations of NAD. Treatment of the pre-formed complex with NAD and PADPR synthetase had no effect on its salt-induced dissociation. This suggests that either poly(ADP-ribosylation) has no influence on dissociation of topoisomerase, in contrast to association, or topoisomerase is not accessible to the synthetase when bound to DNA. Similar data were obtained with calf thymus type I topoisomerase.
...
PMID:Inhibition of calf thymus type II DNA topoisomerase by poly(ADP-ribosylation). 299 83

In the absence of DNA aggregation, spermidine inhibited the relaxation of negatively supercoiled DNA by Escherichia coli topoisomerase I at concentrations of the polyamine normally found intracellularly. Spermidine also curtailed the cleavage of negatively supercoiled ColE1 DNA by the enzyme in the absence of Mg2+. On the contrary, knotting of M13 single-stranded DNA circles catalyzed by topoisomerase I was stimulated by the polyamine. Relaxation of supercoiled DNA by eukaryotic type 1 topoisomerases, such as calf thymus topoisomerase I and wheat germ topoisomerase, was significantly stimulated by spermidine in the same range of concentrations that inhibited the prokaryotic enzyme. In reactions catalyzed by S1 nuclease, the polyamine enhanced the digestion of single-stranded DNA and inhibited the nicking of negatively supercoiled DNA. These results suggest that spermidine modifies the supercoiled duplex substrate in these reactions by modulating the degree of single strandedness.
...
PMID:Differential modulation by spermidine of reactions catalyzed by type 1 prokaryotic and eukaryotic topoisomerases. 300 Apr 18

Antitumor drugs from many chemical classes have been shown to induce protein-linked DNA breaks in cultured mammalian cells and in vitro in the presence of purified mammalian DNA topoisomerase II. The possibility that mammalian DNA topoisomerase II is an intracellular target which mediates drug-induced DNA breaks is supported by the following studies using 4'-(9-acridinylamino)methane-sulfon-m-anisidide (m-AMSA): (a) a single m-AMSA-dependent DNA cleavage activity copurified with calf thymus DNA topoisomerase II activity at all chromatographic steps of the enzyme purification; (b) m-AMSA-induced DNA cleavage by this purified activity resulted in the covalent attachment of protein to the 5'-ends of the DNA via a tyrosyl phosphate bond. This covalently linked protein has the same reduced molecular weight as purified calf thymus DNA topoisomerase II. The possibility that topoisomerase II-mediated DNA breaks may be responsible for cytotoxicity has also been investigated using a number of m-AMSA-related acridines. The level of topoisomerase II-mediated DNA breaks in vitro strongly correlates with the level of protein-linked DNA breaks in cultured cells and drug-induced cytotoxicity. These results suggest that mammalian DNA topoisomerase II may be a cytotoxic target of antitumor acridines.
...
PMID:DNA damage by antitumor acridines mediated by mammalian DNA topoisomerase II. 300 16

Type I topoisomerases have been purified from nuclei and mitochondria of human acute lymphoblastic leukemia cells. Both of these ATP-independent enzymes are actually found to be inhibited by ATP at physiologically significant concentrations. Other adenine nucleotides showed varying effects: ADP inhibited only at high concentrations; AMP had no effect on either topoisomerase. Both enzymes were also inhibited by dATP. The importance of the adenine ring structure was confirmed by the lack of an inhibitory effect observed with equivalent levels of GTP, UTP, CTP, or their deoxy counterparts. Assays performed in the presence of nonhydrolyzable analogs of ATP suggest that hydrolysis of ATP does not accompany this enzyme inhibition. This was supported by direct determination of the ATPase activity of the purified enzymes. Type I topoisomerase from calf thymus and HeLa cells were also found to be sensitive to ATP. These results suggest that mammalian type I topoisomerases in general may possess a nucleotide-binding site that may be involved in regulation of enzyme activity.
...
PMID:ATP inhibits nuclear and mitochondrial type I topoisomerases from human leukemia cells. 300 64

The DNA topoisomerase I has been isolated from neurons of rat cerebral cortex. The most homogeneous fraction purified contains only one polypeptide of Mr approx. 100 000. The enzyme relaxes supercoiled DNA in the absence of ATP or Mg2+. The optimum monovalent cation concentration for the relaxation of superhelical DNA under conditions of DNA excess is found to be 175-200 mM. The neuron enzyme is similar to other mammalian type I DNA topoisomerases in that it links to the 3' ends of the broken DNA strands. Like calf thymus DNA topoisomerase I, the neuron topoisomerase can be selectively inhibited by poly(dG) but not by other homopolymerical deoxyribonucleotides.
...
PMID:DNA topoisomerase I from rat brain neurons. 300 75

The influence of ciprofloxacin, nalidixic acid, norfloxacin, novobiocin, and ofloxacin on elements of eucaryotic DNA replication was investigated in vitro. Each of the 4-quinolones, when present in amounts of more than 100 micrograms/ml, reversibly inhibited the DNA synthesis performed by the 95 DNA polymerase alpha primase complex from calf thymus. Novobiocin at 500 micrograms/ml or at higher concentrations irreversibly inactivated DNA polymerase alpha primase complex. The accuracy of in vitro DNA synthesis in the absence of repair mechanisms was determined from amber-revertant assays with phi X174am16(+) DNA as template. The antimicrobial agents did not significantly increase the frequencies of base pairing mismatches during the course of replication, indicating that the basal mutation rate is not affected by novobiocin and the 4-quinolones. The Ki values of 50% inhibition of DNA topoisomerases from calf thymus by ciprofloxacin, norfloxacin, novobiocin, nalidixic acid, and ofloxacin were 300, 400, 1,000 or more, 1,000 or more, and 1,500 or more micrograms/ml, respectively, in the case of topoisomerase I, and the Ki values were 150, 300, 500, 1,000, and 1,300 micrograms/ml, respectively, in the case of topoisomerase II. The procaryotic topoisomerase II is approximately 100-fold more sensitive to inhibition by ciprofloxacin, norfloxacin, and ofloxacin than is its eucaryotic counterpart. Growth curves of lymphoblasts were recorded in the presence of ofloxacin and ciprofloxacin. Neither 1 nor 10 micrograms of ciprofloxacin or of ofloxacin per ml affected cell proliferation. Ofloxacin and ciprofloxacin at 100 micrograms/ml inhibited cell growth; 1,000 micrograms/ml led to cell death. No correlation exists between the antimicrobial and cytotoxic activities of the 4-quinolones.
...
PMID:Effect of 4-quinolones and novobiocin on calf thymus DNA polymerase alpha primase complex, topoisomerases I and II, and growth of mammalian lymphoblasts. 301 15

We have analyzed 1 kb of cloned human c-fos sequence (-711 to +287) for calf thymus DNA topoisomerase II cleavage sites in vitro. Using the anti-tumor drug VP16 (demethylepipodophyllotoxin-beta-D-glucoside) with purified topoisomerase II, we identify twelve sites. Five sites are clustered around position -306 in a region that possesses enhancer-like properties. A second cluster of three sites is positioned 15 bp upstream of the TATA promoter element. With a HeLa nuclear extract as a source of topoisomerase II, a subset of cleavage sites is conserved within the two clusters. The cleavage sites in the enhancer-like element are conserved in the homologous region of the murine c-fos. These findings raise the possibility that topoisomerase II is involved in mediation of mitogen-induced c-fos expression.
...
PMID:DNA topoisomerase II cleaves at specific sites in the 5' flanking region of c-fos proto-oncogenes in vitro. 302 64

DNA topoisomerase II was purified from calf thymus nuclei by a simple and fast four-step procedure: selective ammonium sulfate precipitation, chromatography on blue-Sepharose and hydroxyapatite, followed by ultracentrifugation on a glycerol gradient. Starting from 300 g thymus glands, this procedure yields 0.7 mg of homogeneous topoisomerase II. The final product is free of any nucleolytic, proteolytic or topoisomerase I activity. Dodecylsulfate/polyacrylamide gel electrophoresis reveals two bands with apparent molecular masses of 175 and 150 kDa. Analytical gel filtration and sedimentation on isokinetic sucrose gradients were used to determine the Stokes' radius as 6.4 nm and the sedimentation coefficient as 9.5 S, indicating a dimeric structure for the native enzyme. The purified topoisomerase II is strictly dependent on ATP or dATP, the Km values of which were 0.14 mM and 0.5 mM, respectively. Mg2+ is an essential cofactor for the reaction at concentrations between 0.5-8 mM, with an optimum at 4 mM. Mg2+ can be substituted by Mn2+ at concentrations between 0.2-0.4 mM. Both the relaxation and the catenation reaction exhibit a salt optimum at 130 mM NaCl. At concentrations below 30 mM and above 200 mM, the enzyme is inactive. The pH is optimal between 8 and 9.5 using Tris buffers.
...
PMID:Purification and characterization of DNA topoisomerase II from calf thymus associated with polypeptides of 175 and 150 kDa. 302 77

In an attempt to get an insight into the activity of mAMSA (a DNA topoisomerase II-mediated drug) on the human proto-oncogene c-myc, an in vitro system consisting of purified calf thymus DNA topoisomerase II and a c-myc DNA inserted in lambda phage was utilized. The occurrence of discrete bands, detected by hybridization of Southern blots with appropriate c-myc probes, indicated the presence of cleavage sites in the sole presence of DNA topoisomerase II. The band intensity increased in the presence of mAMSA, while no significant difference occurred in the cleavage pattern. The location of the cleavage sites along the c-myc locus revealed a striking correspondence with that of some DNase hypersensitive sites. These results indicate that DNA topoisomerase II is most certainly implicated in the mAMSA activity and that the drug stimulates the topoisomerase II cleaving activity at specific sites, which may be involved in the biological activity of the drug.
...
PMID:Characterization of the topoisomerase II-induced cleavage sites in the c-myc proto-oncogene. In vitro stimulation by the antitumoral intercalating drug mAMSA. 302 49

The fraction DE-B obtained by fractionating an extract from rat mammary adenocarcinoma cells on a DEAE-Sephadex column was used for transcribing linear and supercoiled rRNA gene (rDNA). This fraction, which is known to contain RNA polymerase I and essential transcription factors, also contains DNA topoisomerase I activity. Inhibition of this topoisomerase activity by the selective inhibitor camptothecin markedly diminished transcription of supercoiled rDNA, and at a concentration of 150 microM, camptothecin almost completely inhibited DNA topoisomerase I activity and supercoiled rDNA transcription. Addition of exogenous calf thymus DNA topoisomerase I to the sample containing the drug restored the ability of the extract to transcribe supercoiled rDNA. Camptothecin, even at a concentration of 500 microM, had no significant effect on the transcription of linear rDNA. These studies show that relaxation of supercoiled rDNA by DNA topoisomerase I is essential for its transcription. The preferential inhibition of rRNA synthesis in vivo following treatment with camptothecin is probably due to selective camptothecin inhibition of DNA topoisomerase I activity.
...
PMID:Role of DNA topoisomerase I in the transcription of supercoiled rRNA gene. 303 39


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

---