Fluorescence quenching was used to study the interactions of DNA, in the presence and absence of metal ions, with various bleomycin (BLM) analogs, which include the active BLM A2 [11116-31-7], BLM B1' [41138-54-9], tallysomycin A (TLM A) [65057-90-1], desamido-BLM A2 [65154-36-1], 3 less active BLM A2 analogs with a substitution at the α-amino group of the β-aminoalanine, and 2 inactive TLM fragments (Wa [70518-45-5] and Wb [70518-46-6]).All drugs had a nonionic type DNA-induced fluorescence quenching of 20-30% but varied in the extent of the ionic type of quenching as follows: TLM A, Wa, and Wb, 50-60%; BLM A2, 20-25%; BLM B1 and desamido-BLM A2, <10%; the 3 α-amino-substituted BLM A2 analogs, 0%.There was no apparent correlation of the overall DNA breakage activity of drugs with the extent of either type of quenching.The DNA-drug interactions as seen by quenching effects were not sufficient for breakage activity.Modification at the α-amino group completely eliminated the ionic quenching and reduced the nonionic type.The removal of the terminal amide group of the β-aminoalanine as in desamido-BLM A2 markedly reduced the ionic quenching, whereas an increase in the pos. charge of the C-terminal amine enhanced the ionic quenching.Thus, both the β-aminoalanine and the C-terminal amine may be essential for the ionic type of quenching effect, which may be associated with the DNA double-strand breakage activity of BLM since such activity was very low in desamido-BLM A2 in contrast to BLM A2.Apparently, at high ionic strength, the removal of the amide or the loss of the pos. charge in the terminal amine minimally affected the binding constant but reduced the number of available binding sites by 50%.These residual sites are nonionic in nature.The overall quenching effect had a base and sequence preference consistent with the reported GC, GT, and TA specificity of the DNA breakage.The quenching effects of DNA and FeCl2 or CuCl2 were additive.β-Mercaptoethanol, which had a differential effect on FeCl2- and CuCl2-induced quenching, had little effect on the DNA-induced quenching.
