The sensitivity to camptothecin of DNA topoisomerase I in L5178Y-S lymphoma cells.
Sensitivity to camptothecin (CPT) of type I DNA topoisomerases isolated from two L5178Y (LY) sublines was examined in reaction media containing either aspartate or chloride. The enzyme from LY-S cells was sensitive to the drug in the presence of 120 mM K-aspartate, but the sensitivity was markedly reduced in the presence of 120 mM KCl. The enzyme from LY-R cells was similarly sensitive to camptothecin in the presence of either aspartate or chloride. The optimum ionic strength for the relaxation reaction catalyzed by both LY-R and LY-S type I DNA topoisomerases was similar. We suggest that sensitivity of the LY-S enzyme to CPT depends on the amount of cleavable complex formed, which in turn depends on the ionic conditions of the assay.
Staron
K
K
Institute of Biochemistry, Warsaw University, Poland.
Kowalska-Loth
B
B
Szumiel
I
I
D000818:Animals; D001224:Aspartic Acid / Q000494:pharmacology; D002166:Camptothecin / Q000494:pharmacology*; D004351:Drug Resistance; D007940:Leukemia L5178 / Q000201:enzymology*; D051379:Mice; D009363:Neoplasm Proteins / Q000037:antagonists & inhibitors*; D011189:Potassium Chloride / Q000494:pharmacology; D059004:Topoisomerase I Inhibitors; D014407:Tumor Cells, Cultured
D009363:Neoplasm Proteins; D059004:Topoisomerase I Inhibitors; D001224:Aspartic Acid; D011189:Potassium Chloride; D002166:Camptothecin