RESUMO
Topoisomerase activities have been measured in nuclear extracts of concanavalin A-stimulated lymphocytes. In parallel with the wave of DNA synthesis, type II topoisomerase activity was considerably increased. After 72 h treatment, this activity was stimulated approx. 20-fold over the activity in untreated cells. In contrast, type I topoisomerase was poorly stimulated after 24 h treatment, and 4-5-fold after 72 h. These findings, together with our previous results on regenerating rat liver, suggest a major role of topoisomerase II in DNA replication.
Assuntos
Concanavalina A/farmacologia , DNA Topoisomerases Tipo I/sangue , Ativação Linfocitária , Linfócitos/enzimologia , Animais , Núcleo Celular/enzimologia , Replicação do DNA , Eletroforese em Gel de Ágar , Cobaias , Fatores de TempoAssuntos
DNA Topoisomerases Tipo II/isolamento & purificação , DNA Circular/metabolismo , Fígado/metabolismo , Trifosfato de Adenosina/farmacologia , Aminocumarinas , Animais , Cumarínicos/farmacologia , DNA Topoisomerases Tipo II/metabolismo , DNA Super-Helicoidal/metabolismo , Histonas/farmacologia , Técnicas In Vitro , Regeneração Hepática , Novobiocina/farmacologia , Conformação de Ácido Nucleico , Ratos , Inibidores da Topoisomerase IIRESUMO
Besides the nicking-closing (topoisomerase I) activity, an ATP-dependent DNA topoisomerase is present in rat liver nuclei. The enzyme, partially purified, is able to catenate in vitro closed DNA circles in a magnesium-dependent, ATP-dependent, histone H1-dependent reaction, and to decatenate in vitro kinetoplast DNA networks to yield free minicircles in a magnesium-dependent and ATP-dependent reaction. It is largely similar to other eukaryotic type II topoisomerases in its requirements, and presumably belongs to this class of enzymes. Type I and type II activities were measured in rat liver nuclei as a function of regenerating time after partial hepatectomy: type I activity was not significantly changed during this process. In contrast, type II activity was considerably increased, suggesting a possible involvement of the enzyme in DNA replication.
