Inhibition of the reactions catalysed by a type I topoisomerase and catenating enzyme of Trypanosoma cruzi by DNA-intercalating drugs. Preferential inhibition of the catenating reaction.

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Abstract
A catenating enzyme and a type I topoisomerase were purified from Trypanosoma cruzi. We investigated the inhibitory effect of DNA‐intercalating drugs on topoisomerisations catalysed by these enzymes. Inhibition of catenation was detected by electrophoretic analysis in neutral agarose gels. However, the inhibition of relaxation was not readily detectable in these gels since supercoiled DNA, which was relaxed in the presence of an intercalating drug, returned to a supercoiled state when the drug was removed. Thus electrophoretic analyses were made in gels containing chloroquine so that unreacted DNA could be distinguished from DNA relaxed by the enzyme. The results show that the catenation was more sensitive to DNA‐intercalating drugs than the relaxation.