An inhibitor of DNA topoisomerase I from Xenopus laevis ovaries.
A novel, heat-resistant and Pronase-sensitive, inhibitor of eukaryotic DNA topoisomerase I has been purified from Xenopus laevis ovaries. Sodium dodecyl sulfate-polyacrylamide gel electrophoresis (SDS-PAGE) of the most purified fraction revealed three bands with apparent molecular masses of 25, 28.5, and 33.5 kDa. The 25- and 33.5-kDa peptides recovered from an SDS-PAGE gel inhibited X. laevis DNA topoisomerase I. The purified inhibitor was specific to DNA topoisomerase I and did not inhibit other DNA enzymes tested. The inhibitor blocked the catalytic activity of DNA topoisomerase I by interacting with the enzyme, rather than by competing for binding sites on substrate DNA. Binding of DNA topoisomerase I to substrate DNA was blocked by the inhibitor, as was the cleavage reaction catalyzed by DNA topoisomerase I. Inhibition of DNA topoisomerase I was relieved by divalent cations Ca2+, Mg2+, or Mn2+.
Department of Zoology and Genetics, Iowa State University, Ames 50011-3223.
J
J
Zhao
R M
RM
Benbow
D000818:Animals; D001667:Binding, Competitive; D002118:Calcium / Q000494:pharmacology; D002845:Chromatography; D002850:Chromatography, Gel; D002852:Chromatography, Ion Exchange; D004264:DNA Topoisomerases, Type I / Q000302:isolation & purification; D017886:Durapatite; D004591:Electrophoresis, Polyacrylamide Gel; D004791:Enzyme Inhibitors / Q000302:isolation & purification* / Q000494:pharmacology; D005260:Female; D007700:Kinetics; D008274:Magnesium / Q000494:pharmacology; D008345:Manganese / Q000494:pharmacology; D010053:Ovary / Q000201:enzymology*; D011485:Protein Binding; D011506:Proteins / Q000302:isolation & purification* / Q000494:pharmacology; D059004:Topoisomerase I Inhibitors; D014982:Xenopus laevis
D004791:Enzyme Inhibitors; D011506:Proteins; D059004:Topoisomerase I Inhibitors; D008345:Manganese; D017886:Durapatite; D004264:DNA Topoisomerases, Type I; D008274:Magnesium; D002118:Calcium