English: Figure 2. Mechanism of bleomycin-mediated DNA cleavage. The Bleomycin-Fe(III)-OOH activated form is generated in the presence of a one-electron reductant, Fe2+ and oxygen. The activated bleomycin then abstracts the hydrogen atom (red square) from C4′ of the deoxyribose moiety of DNA to form the intermediate 4′ radical. This intermediate can partition into two pathways. In the abundance of oxygen, the 4′ radical initiates a series of chemical transformations, leading to a direct strand break and producing 3′-phosphoglycolate and 5′-phosphate ends, and release of a base propenal. However, in the absence of oxygen, the intermediate reacts with an oxidant in the presence of water, generating 4′-oxidized abasic sites. The figure is adapted from [15] and reprinted by permission from Springer Nature.