Streptonigrin-transition metal complexes: binding to DNA and biological activity.

Summary Two effects of transition metal divalent cations on the behavior of the antitumor antibiotic streptonigrin are reported: (1) Metal ions such as Mn ++ , Zn ++ , and Cd ++ promote an association of the antibiotic with double-stranded DNA. The metal ion causes a depression and slight red shift of the 365 nm absorption maximum of the antibiotic. Addition of DNA to the zinc-streptonigrin complex causes a further depression and red shift of the absorption maximum, indicating the formation of a DNA-streptonigrin-zinc complex. (2) These metal cations affect the biological activity of streptonigrin, in that they greatly enhance the lethal effect of the antibiotic on Escherichia coli . It is likely that the two effects are related.