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  • 1
    Electronic Resource
    Electronic Resource
    Effect of CPT on the DNA cleavage/religation reaction mediated by calf thymus Topoisomerase I: evidence of an inhibition of DNA religation (1994)
    Springer
    Molecular biology reports 20 (1994), S. 129-133 
    Details
    ISSN: 1573-4978
    Keywords: Topoisomerase I ; eleavage/religation equilibrium ; camptothecin
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Abstract The uncoupling of the calf thymus Topoisomerase I-mediated forward DNA cleavage reaction from the religation event by a rapid shift of cleavage temperature either from 37 °C to 0 °C or from 37 °C to 56 °C has been studied and utilized to elucidate the molecular mechanism by which camptothecin, a clinically relevant antineoplastic agent, influences the half reactions of the enzyme. Results of heating and cooling religation-inducing treatments have been compared: both temperature extremes reduce the amount of protein-linked DNA breaks to background levels, thereby affecting cleavage reversal. Camptothecin is found to stabilize the enzyme-DNA intermediate, by inhibition of the Topoisomerase I-mediated rejoining of cleaved DNA, even when the drug is added after formation of the complex. We conclude that: 1. Heating and cooling treatments show a pronounced effect on the DNA cleavage-religation equilibrium. The efficacy of cold is more pronounced than that of heat. 2. Reversal of the enzyme-DNA intermediate favors the DNA resealing versus the closed relaxed form. 3. Camptothecin affects the heat or cold induced religation: in fact in both cases the drug delays the religation step.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00990544
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    Paper (German National Licenses)
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  • 2
    Electronic Resource
    Electronic Resource
    Optimum DNA relaxation reaction conditions for calf thymus DNA-Topoisomerase I are determined by specific enzyme features (1990)
    Springer
    Molecular biology reports 14 (1990), S. 255-259 
    Details
    ISSN: 1573-4978
    Keywords: calf thymus ; DNA-Topoisomerase I ; optimal reaction conditions
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Abstract Reactivity and chemical properties of calf thymus Topoisomerase I have been investigated with respect to enzyme ability to relax supercoiled DNA. The relaxation rate has been analyzed at optimum and relatively high salt concentration. Catalysis is processive at optimum salt concentration and distributive at a higher one; camptothecin decreases the initial rate of reaction in both salt conditions, but more so at the higher one. We conclude that: 1. calf thymus Topoisomerase I requires, for its maximum reactivity, specific and characteristic reaction conditions; 2. salt concentration affects DNA processing, indeed influencing the initial rate of DNA relaxation and directly reflecting the salt-dependence for the enzyme-duplex DNA binding; 3. Topoisomerase I, from various sources, maybe individually responds to alteration of assay parameters such as pH, Mg++ and NaCl concentrations, indicating that individual criteria could be responsible for the catalytic activity optimum.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00429894
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    Paper (German National Licenses)
    Fulltext
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