Effects of O₂ on the reactions of activated bleomycin

The antitumor drug, bleomycin, interacts with either Fe(II) and O₂ or Fe(III) and H₂O₂ to form an activated complex which attacks DNA. Under aerobic conditions, both reactions yield similar quantities of free bases and products consisting of base plus deoxyribose carbon atoms 1 to 3. Under anaerobic conditions, activated bleomycin releases only free base. The yield of free base is the same under aerobic or anaerobic conditions, provided DNA is furnished in excess. When the DNA concentration is limiting, more base is released under anaerobic than under aerobic conditions. Drug self-destruction proceeds as quickly and completely in the presence or absence of O₂.