FIGURE 5.

Human TOPO1 is not inhibited by phenantrene alkaloids. A, effect of compounds 16 (N-methyl-seconeolitsine) and 17 (seconeolitsine) on the enzymatic activity. Supercoiled pBR322 was treated with 1 unit of enzyme in the absence (lanes 0) or in the presence of various concentrations of the alkaloids with or without (lane 30(-)) preincubation 30 μm of compound 17. B, EtBr displacement assay of compounds 16 and 17. Fluorescence is expressed as the percentage of the maximum fluorescence signal when EtBr was bound to the DNA in the absence of the alkaloids and was corrected for background fluorescence of EtBr in solution.