Photo-induced nicking of deoxyribonucleic acid by ruthenium(II)-bleomycin in the presence of air.

A new metallobleomycin, ruthenium(II)-bleomycin A2 was prepared. When irradiated at 366 nm the ruthenium complex (1-10 microM) was found to break a 121-base pair DNA restriction fragment at specific sites (usually the pyrimidine residues located at the 3'-side of guanine). Care was taken to rule out complications due to the presence of trace amounts of iron. Photo-induced damage by cobalt-bleomycin in the presence of light, and redox-mediated damage by bleomycin and iron produced DNA cleavage at sites similar to ruthenium-bleomycin. In contrast to cobalt-bleomycin, ruthenium-bleomycin required oxygen as well as light to cause significant damage to DNA.