Topoisomerase activity in mitochondrial lysates of a higher plant (Chenopodium album L.).

We describe an in vitro system for detection of topoisomerase activity from lysed mitochondria. Mitochondria were isolated from a suspension of cultured Chenopodium album cells. We observed a high activity in relaxation of negatively supercoiled DNA (pBR322). Addition of ATP had no effect on the activity. Topoisomers obtained from negatively supercoiled DNA were identical with topoisomers produced by the topoisomerase I of E. coli. The mitochondrial activity was dependent on the presence of Mg2+ ions and could be inhibited by novobiocin and N-ethylmaleimide. Nalidixic acid and berenil had no influence on the mitochondrial topoisomerase activity. These features characterize the enzyme as a type I topoisomerase.