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)

A topoisomerase (nicking-closing enzyme) has been isolated from rat liver mitochondria. It has purified by double-stranded DNA-cellulose chromatography approximately 50,000-fold, based on the crude mitochondrial extract. It possesses a minimum specific activity of 1.9 x 10(5) units/mg. The enzyme has been shown to be distinctly mitochondrial, differentiated from the nuclear topoisomerase by its sensitivity to the intercalating drug, ethidium bromide, and to the non-intercalating trypanocidal drug, Berenil.
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PMID:Mitochondria contain a distinct DNA topoisomerase. 22 16

Pentamidine, diminazene aceturate (Berenil), isometamidium chloride (Samorin), and ethidium bromide, which are important antitrypanosomal drugs, promote linearization of Trypanosoma equiperdum minicircle DNA (the principal component of kinetoplast DNA, the mitochondrial DNA in these parasites). This effect occurs at therapeutically relevant concentrations. The linearized minicircles are protease sensitive and are not digested by lambda exonuclease (a 5' to 3' exonuclease), indicating that the break is double stranded and that protein is bound to both 5' ends of the molecule. The cleavage sites map to discrete positions in the minicircle sequence, and the cleavage pattern varies with different drugs. These findings are characteristic for type II topoisomerase inhibitors, and they mimic the effects of the antitumor drug etoposide (VP16-213, a semisynthetic podophyllotoxin analog) on T. equiperdum minicircles. However, the antitrypanosomal drugs differ dramatically from etoposide in that they do not promote detectable formation of nuclear DNA-protein complexes or of strand breaks in nuclear DNA. Selective inhibition of a mitochondrial type II topoisomerase may explain why these antitrypanosomal drugs preferentially disrupt mitochondrial DNA structure and generate dyskinetoplastic trypanosomes (which lack mitochondrial DNA).
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PMID:Selective cleavage of kinetoplast DNA minicircles promoted by antitrypanosomal drugs. 215 80

A type I topoisomerase has been purified more than 4000-fold from calf thymus mitochondria. The enzyme is membrane associated and is effectively solubilized by 1% Triton X-100 treatment of purified mitochondrial inner membranes. This ATP-independent enzyme relaxes positively and negatively supercoiled DNA with delta LK = 1. At low ionic strength, the native enzyme appears to be a monomer (sedimentation coefficient of 4.3 S and Stokes radius of 34 A), but it can form a weakly associated dimer at higher salt concentrations (sedimentation coefficient of 7.0 S and Stokes radius of 47.5 A). The mitochondrial type I topoisomerase is distinguishable from the nuclear enzyme by its (1) pH profile, (2) thermal stability, (3) response to dimethyl sulfoxide and Berenil, and (4) molecular weight. The mitochondrial enzyme is inhibited by elevated concentrations of the bacterial DNA gyrase inhibitor novobiocin, but not nalidixic or oxolinic acids. Sensitivity to N-ethylmaleimide indicates the importance of cysteine for catalytic activity. It is estimated that there are at least five copies of topoisomerase I per mammalian mitochondrion or a minimum of one to two per mitochondrial genome. In a manner similar to that observed with leukemia (nuclear and mitochondrial), calf thymus (nuclear), and HeLa (nuclear) cell type I topoisomerase, the calf thymus mitochondrial enzyme is inhibited by physiological concentrations of ATP.
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PMID:Purification and characterization of a type I DNA topoisomerase from calf thymus mitochondria. 282 74

We have reported previously that rat liver mitochondria contain a topoisomerase and have shown it to be distinct from the nuclear enzyme by its sensitivity to Berenil and ethidium bromide. We report here some additional characterization. The enzyme differs further from its nuclear counterpart in its failure to bind to ssDNA cellulose and its chromatographic behavior on Sephadex; the latter procedure yields an Mr of 44 000 for the mitochondrial and 70 000 for the nuclear enzyme. The topoisomerase is strongly associated with mitochondrial membranes; only 10% of the activity could be extracted. The pH optimum of the enzyme falls between 6.0 and 8.5, with an NaCl optimum of 0.13 M in 0.1 M Tris (pH 8.3). Dithiothreitol is required, while N-ethylmaleimide is inhibitory. Tosylphenylalanine chloromethyl ketone, a serine proteinase inhibitor, abolishes activity; another, phenylmethanesulfonyl fluoride, has no effect. Berenil, a non-intercalating drug, and four of its analogues all inhibit with up to 100-fold differences in potency. No dependence on ATP, Mg2+, or both together could be shown. Neither novobiocin nor oxolinic acid shows any inhibitory effect. Nicked circles are generated in the presence of DMSO. These three observations are consistent with the topoisomerase being of the Type I class. Positively supercoiled pBR322 DNA, whose 6-8 positive turns were generated by altering solution conditions, is relaxed by the enzyme, indicating a lack of requirement for a negatively supercoiled substrate. We have also examined a partially purified preparation of the corresponding mitochondrial enzyme from mouse L cells. This enzyme is largely similar in properties to the rat liver enzyme. In isolated mitochondria, Berenil causes biphasic alterations in [3H]dATP incorporation into DNA, 10(-4) mM stimulating 2-fold, while higher concentrations inhibit. [3H]UTP incorporation into mitochondrial RNA also follows this pattern.
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PMID:Studies on mitochondrial type I topoisomerase and on its function. 298 52

A type I topoisomerase has been purified to near homogeneity from the trypanosomatid Crithidia fasciculata. The topoisomerase consists of a single 79 kDa polypeptide. The enzyme does not require divalent cations but is stimulated 10-20 fold by the presence of MgCl2. ATP does not affect enzyme activity, while Berenil, N-ethylmaleimide and ethidium bromide are inhibitory. Immunoblots show that the 79 kDa polypeptide is the most prevalent form of the enzyme in extracts of freshly lysed cells and is immunogenically conserved among a variety of trypanosomes. The topoisomerase was localized to the cell nucleus by double antibody immunofluorescence.
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PMID:Purification and nuclear localization of a type I topoisomerase from Crithidia fasciculata. 304 Dec 12