THE INFLUENCE OF ANTIBIOTICS AND ANTITUMOR AGENTS ON THE RELAXATION ACTIVITY OF PISUM-SATIVUM LEAF CHLOROPLAST TOPOISOMERASE-I

DNA topoisomerase was isolated from pea leaf chloroplasts. The relaxat ion activity of this topoisomerase was Mg2+ dependent and sensitive to ethidium bromide and novobiocin, a gyrase inhibitor. Chloroplast topo isomerase (Topo I) was ATP independent, as shown by the characteristic gel distribution of topoisomers. Topoisomerase, compared with the kno wn eucaryotic topoisomerase I, was not stimulated by polyamines as are spermidine, spermine, and cadaverine. Ethidium bromide, DAPI, heparin , nalidixic acid, and m-AMSA (but not camptothecin) were able to inhib it the relaxation activity of chloroplast topo I. Nalidixic acid, novo biocin, m-AMSA, camptothecin, and amiloride were tested for their effe cts on the topo-isomerase-catalyzed ''cleavage complex'' between DNA a nd chloroplast DNA topoisomerase I. (C) 1995 Academic Press, Inc.