These tools will no longer be maintained as of December 31, 2024. Archived website can be found here. PubMed4Hh GitHub repository can be found here. Contact NLM Customer Service if you have questions.


Pubmed for Handhelds

PUBMED FOR HANDHELDS

Search MEDLINE/PubMed

  • Title: Purification and characterization of Xenopus laevis type I topoisomerase.
    Author: Attardi DG, De Paolis A, Tocchini-Valentini GP.
    Journal: J Biol Chem; 1981 Apr 25; 256(8):3654-61. PubMed ID: 6260773.
    Abstract:
    A topoisomerase activity was purified from mature ovaries and from nuclei of stage 6 oocytes of Xenopus laevis. From both preparations we obtained a single polypeptide chain having an estimated molecular weight of 67,000. The enzyme purified from ovaries is active in the presence of 150 mM monovalent cation, but its activity is more than 1 order of magnitude higher in the presence of 6 mM Mg2+; the enzyme purified from nuclei requires Mg2+ through all the steps of purification. Enucleated oocytes are devoid of topoisomerase activity but are able to convert the nuclear enzyme to a species active also in the presence of monovalent cations. The difference in ionic requirement between the nuclear topoisomerase and the enzyme purified from ovaries as well as the topoisomerases from other eukaryotic sources, which are most active in the presence of monovalent cations, may depend on the source of the enzyme and/or on the extraction procedure. Ovarian and nuclear topoisomerases catalyze relaxation of both negatively and positively superhelical DNA; the relaxed isomers produced in the presence of Mg2+ have a few positive superhelical turns.
    [Abstract] [Full Text] [Related] [New Search]