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

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Query: EC:5.99.1.2 (topoisomerase)
9,166 document(s) hit in 31,850,051 MEDLINE articles (0.00 seconds)

This study compares the effects of the epipodophyllotoxin derivatives, VM-26 and VP-16, and the 9-anilinoacridine derivatives, m-AMSA and o-AMSA, on nascent and mature DNA. Two types of lesion which are putatively mediated by topoisomerase II, DNA-protein crosslinks and DNA double-strand breaks, were analyzed in drug-treated nuclei from 3H/14C labelled L1210 cells. Potassium/dodecyl sulfate precipitation assay was used to assess DNA-protein crosslinks in mature and nascent (1 min old) DNA. Both epipodophyllotoxins and m-AMSA showed a strong preference for nascent DNA. DNA double-strand cleavage induced by VM-26 and m-AMSA also showed a preference for nascent DNA as indicated by neutral elution technique. Sedimentation on neutral sucrose gradients revealed that these drugs generated highly degraded fragments (under 30 S) in nascent DNA substantially faster than in mature DNA. Lesions in nascent DNA were diminished substantially by the omission of ATP or the addition of novobiocin. The ability to induce lesions in nascent DNA correlates with cytotoxic potency of the agents studied. The results suggest that replicating DNA may constitute a preferential target for antitopoisomerase II drugs.
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PMID:Topoisomerase-II-mediated lesions in nascent DNA: comparison of the effects of epipodophyllotoxin derivatives, VM-26 and VP-16, and 9-anilinoacridine derivatives, m-AMSA and o-AMSA. 283 25

We report here the large scale purification of DNA topoisomerase II from calf thymus glands, using the unknotting of naturally knotted P4 phage DNA as an assay for enzymatic activity. Topoisomerase II was purified more than 1300-fold as compared to the whole cell homogenate, with 22% yield. Analysis of the purified enzyme by sodium dodecyl sulfate-polyacrylamide gel electrophoresis revealed two bands of apparent molecular masses of 125 and 140 kDa. Tryptic maps of the two bands indicated that they derive from the same protein. Using these fragments, specific polyclonal antisera to topoisomerase II were raised in rabbits. Immunoblotting of whole cell lysates from various species indicated that topoisomerase II is well conserved among mammals and has a native subunit molecular mass of 180 kDa. Analytical sedimentation and gel filtration were used to determine a sedimentation coefficient of 9.8 S and a Stokes radius of 68 A. The calculated solution molecular mass of 277 kDa implies a dimer structure in solution. The purified topoisomerase II unknots P4 DNA in an ATP-dependent manner and is highly stimulated in its relaxation activity by ATP. A DNA-stimulated ATPase activity, as has been found with other type II topoisomerases, is associated with the purified enzyme. Approximate kinetic parameters for the ATPase reaction were determined to be: a Vmax of 0.06 nmol of ATP/(micrograms of protein) (min) and Km of 0.2 mM in the absence of DNA, and a Vmax of 0.2 nmol of ATP/(micrograms of protein) (min) and Km of 0.4 mM ATP in the presence of supercoiled plasmid DNA.
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PMID:Purification and characterization of a type II DNA topoisomerase from bovine calf thymus. 298 21

The nucleotide preferences of calf thymus topoisomerases I and II for recognition of supercoiled DNA have been assessed by the relaxation and cleavage of DNA containing base-specific phosphorothioate substitutions in one strand. The type I enzyme is inhibited to varying degrees by all modified DNAs, but most effectively (by approximately 60%) if deoxyguanosine 5'-O-(1-thiomonophosphate) (dGMP alpha S) is incorporated into negatively supercoiled DNA. A DNA in which all internucleotide linkages of one strand are phosphorothionate is relaxed, most probably via the unsubstituted strand. The type II enzyme is inhibited when deoxyadenosine 5'-O-(1-thiomonophosphate) (dAMP alpha S) or deoxyribosylthymine 5'-O-(1-thiomonophosphate) is incorporated into the DNA substrate, and the course of the relaxation reaction changes from a distributive mode to a predominantly processive mode. A fully substituted DNA is very poorly relaxed by the type II enzyme, illustrating the strict commitment of the enzyme to relaxation via double-strand cleavage. The sense of supercoiling does not affect the inhibition profile of either enzyme. DNA strand breaks introduced by type II topoisomerase in a normal control DNA or deoxycytidine 5'-O-(1-thiomonophosphate)-substituted DNA on treatment with sodium dodecyl sulfate at low ionic strength are prevented by pretreatment with 0.2 M NaCl. In contrast, breaks in DNA having either dAMP alpha S or all four phosphorothioate nucleotides incorporated in one strand are prevented only with higher NaCl concentrations. Thus indicating activity at the phosphorothioate linkage 5' to dA but not 5' to dC. We conclude that topoisomerase II activity occurs preferentially at sites possessing dAMP or dTMP, and that dGMP is involved in DNA recognition by topoisomerase I.
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PMID:Relaxation of supercoiled phosphorothioate DNA by mammalian topoisomerases is inhibited in a base-specific manner. 298 7

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.
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PMID:Purification and characterization of DNA topoisomerase II from calf thymus associated with polypeptides of 175 and 150 kDa. 302 77

Lithocholic acid (LCA) is a promoting agent in colon carcinogenesis. In this work we have tried to characterize the DNA alteration induced by LCA in cells grown in vitro and in nuclei. Confirming previous findings, a clear increase in elution rate was observed at both alkaline and neutral pH. The extent of the increase was very similar at the two pHs. However, an increased elution rate could be observed only when lysing the nuclei at high ionic strength and low detergent concentration (2 M NaCl + 0.2% N-lauroylsarcosine sodium salt). No effect could be observed when the nuclei were lysed with a high detergent concentration (2% sodium dodecyl sulfate). In addition, a slight effect could be observed using a method for the evaluation of DNA unwinding in alkali. After termination of the incubation with LCA, the DNA alteration observed with DNA elution disappeared very rapidly both in intact cells and nuclei, even when the incubation buffer was totally unsuitable for the repair of the type of DNA damage induced by typical genotoxic agents. The effect of LCA on DNA was apparently not mediated through an inhibition of topoisomerase II. Only the intact chromatin of nuclei was responsive, not the quasinaked DNA of nuclei lysed at high ionic strength. We advance the hypothesis that the increased alkaline and neutral elution rate observed with LCA could be independent of DNA fragmentation and related to changes in chromatin structure.
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PMID:Characterization of the effects induced on DNA in mouse and hamster cells by lithocholic acid. 356 7

The binding constants for interaction of the anticancer agents mitoxantrone and ametantrone and several congeners with calf thymus DNA and the effects of ionic strength changes have been determined spectrophotometrically. The agents show a preference for certain sequences, particularly those with GC base pairs, and the magnitude of the specificity depends on the specific substituents on the anthraquinone ring system. The binding constant for mitoxantrone with calf thymus DNA in 0.1 M Na+, pH 7, is approximately 6 X 10(6) M-1, and the rate constant for the sodium dodecyl sulfate driven dissociation of mitoxantrone from its calf thymus DNA complex under the same solution conditions and 20 degrees C was determined to be 1.3 s-1. The unwinding angle of mitoxantrone determined independently by viscosity measurements and by a novel assay employing calf thymus topoisomerase shows excellent agreement for a value of 17.5 degrees. The viscosity increase of sonicated calf thymus DNA varies considerably with the substituent on the anthraquinone ring system. Binding studies employing T4 and phi w-14 DNAs in which the major groove is occluded and the reverse experiment with anthramycin-treated calf thymus DNA indicate at least part of the mitoxantrone molecule may lie in the minor groove.
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PMID:Characteristics of the binding of the anticancer agents mitoxantrone and ametantrone and related structures to deoxyribonucleic acids. 405 81

Excision of the lambda prophage from the chromosome of its Escherichia coli host requires the products of the two viral genes int and xis. This paper reports a purification of the lambda xis gene product using a complementation assay in which functional Xis must be added to purified Int and an E. coli-derived host factor extract. Excisive recombination between a left (attL) and right (attR) prophage attachment site cloned on the same plasmid DNA substrate occurred efficiently under these conditions. Purified Int and Xis together could not carry out excision in vitro unless an extract derived from the E. coli host was added; purified integration host factor satisfied this requirement. Xis appears to have a molecular weight of 8800 as determined by polyacrylamide gel electrophoresis in the presence of sodium dodecyl sulfate. It possesses no detectable endonuclease or topoisomerase activities, does not appear to bind DNA to filters, and does not increase the ability of Int to bind DNA. The addition of Xis not only stimulated excisive recombination in vitro but also inhibited integrative recombination. Xis protected Int protein from heat inactivation, suggesting a possible interaction between the two proteins. In light of these observations, possible roles for Xis in recombination are discussed.
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PMID:Purification of the bacteriophage lambda xis gene product required for lambda excisive recombination. 621 11

Wheat germ contains an enzyme capable of removing supercoils from circular DNA. We have purified this enzyme using Polymin P fractionation, ammonium sulfate precipitation, and chromatography on Bio-Rex 70 and phenyl-Sepharose. Renaturation after electrophoresis on sodium dodecyl sulfate-polyacrylamide gels shows that topoisomerase activity is associated with a polypeptide with a Mr = about 111,000. The enzyme is similar to other eukaryotic type I DNA topoisomerases (nicking-closing enzymes) by the following criteria: it is capable of increasing or decreasing the topological linking number of covalently closed DNA substrate; it is capable of restoring an equilibrium distribution of linking numbers to DNA substrate with a single unique linking number; and it does not require magnesium ion or ATP for activity.
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PMID:Purification and characterization of wheat germ DNA topoisomerase I (nicking-closing enzyme). 626 92

A purified preparation of the Escherichia coli integration host factor (IHF) displays two polypeptides of apparent molecular weight 11,000 and 9,500 when analyzed by polyacrylamide gel electrophoresis in the presence of sodium dodecyl sulfate. Under nondenaturing conditions, IHF appears to exist as a 1:1 complex of these two polypeptides. Integrative recombination takes place in vitro when purified IHF and purified Int, a product of a bacteriophage lambda gene, are the only proteins added to reaction mixtures. No recombination is detected in the absence of either protein. The characteristics of the recombination reaction carried out by these two purified proteins are described. Purified IHF binds to DNA; in the presence of Int, a ternary complex is formed at one of the specific recombination sites. IHF hs no detectable endonuclease or topoisomerase activity. Several possibilities for the role of IHF in recombination are considered.
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PMID:Purification and properties of the Escherichia coli protein factor required for lambda integrative recombination. 626 68

Using kinetoplast DNA networks as a substrate in a decatenation assay, we have purified to apparent homogeneity a type II DNA topoisomerase from HeLa cell nuclei. The most pure preparations contain a single polypeptide of 172,000 daltons as determined by sodium dodecyl sulfate-gel electrophoresis. The molecular weight of the native protein, based on sedimentation and gel filtration analyses, is estimated to be 309,000. These results suggest that the enzyme is a dimer of 172,0090-dalton subunits. The enzyme is a type II topoisomerase as demonstrated by its ability to change the linking number of DNA circles in steps of two and to decatenate or unknot covalently closed DNA circles. No gyrase activity is detectable. ATP is required for the relaxation, decatenation, and unknotting of DNA, and a DNA-dependent ATPase activity is present in the most pure fractions. ATP is hydrolyzed to ADP in this properties to T4 DNA topoisomerase (Liu, L. F., Liu, C. C., and Alberts, B. M. (1979) Nature 281, 456-461).
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PMID:A homogeneous type II DNA topoisomerase from HeLa cell nuclei. 626 71


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