title: Mitochondrial DNA topoisomerase I from human platelets.
abstract: An anucleated cell system has been used for the first time to study mitochondrial topoisomerase activity. Mitochondrial extracts from human blood platelets contained type I topoisomerase. The type I classification was based on ATP-independent activity, inhibition by ATP or camptothecin, and the lack of inhibition by novobiocin. Platelet mitochondrial topoisomerase I relaxation activity was inhibited linearly by increasing concentrations of EGTA. Topoisomerase activity greater than 90% inhibited by 175 microM EGTA was partially restored to 16 and 50% of the initial level of activity by the subsequent addition of 50 and 100 microM Ca2+, respectively. Additionally, results from studies of partially purified platelet mitochondrial topoisomerase I were consistent with the crude extract data. This work supports the hypothesis that platelet mitochondria contain a type I topoisomerase that is biochemically distinct from that previously isolated and characterized from cell nuclei.
authors.affiliation: Department of Biological Chemistry, Hahnemann University, Philadelphia, PA 19102.
authors.forename: M J
authors.initials: MJ
authors.lastname: Kosovsky
authors.forename: G
authors.initials: G
authors.lastname: Soslau
mesh_terms: D001792:Blood Platelets / Q000201:enzymology*; D002118:Calcium / Q000494:pharmacology; D002469:Cell Separation; D005591:Chemical Fractionation; D004264:DNA Topoisomerases, Type I / Q000097:blood* / Q000187:drug effects; D004533:Egtazic Acid / Q000494:pharmacology; D004793:Enzyme Reactivators; D006801:Humans; D008928:Mitochondria / Q000201:enzymology*; D059004:Topoisomerase I Inhibitors
chemical_list: D004793:Enzyme Reactivators; D059004:Topoisomerase I Inhibitors; D004533:Egtazic Acid; D004264:DNA Topoisomerases, Type I; D002118:Calcium