Copper-bleomycin has no significant DNA cleavage activity.

In contrast to a very recent report [Ehrenfeld, G. M., Rodriguez, L. O., Hecht, S. M., Chang, C., Basus, V. J., & Oppenheimer, N. J. (1985) Biochemistry 24, 81-92], the present careful reexamination demonstrated that copper-bleomycin systems have no significant DNA cleavage activity. In the presence of dithiothreitol, the bleomycin-Cu(II) complex showed little activity for DNA degradation. The DNA strand scission by the Cu(I)-bleomycin-dithiothreitol system was remarkably depressed by deferoxamine rather than by bathocuproine, suggesting the effect of trace amounts of contaminating iron in the experiments. It seems highly unlikely that the DNA breakage activity due specifically to the Cu(I)-bleomycin complex system is substantially strong. Our results indicate that the metal really relevant to the DNA cleavage by bleomycin is iron not copper.