An active intermediate formed in the reaction of bleomycin-Fe(II) complex with oxygen.

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Abstract
The base-release activity of oxygen adduct of bleomycin-Fe(II) complex [BLM-Fe(II)] from DNA decreased with a half-life of 5.2 min, when incubated at 0.degree. C in 0.05 M Tris-HCl buffer at pH 7.8 in the absence of DNA. Under the same condition visible and ESR spectra showed that the adduct was immediately converted into the ferric complex. The ESR study further indicated the simultaneous formation of 2 kinds of the low-spin BLM-Fe(III) complex. One of them disappeared in parallel with the decrease of the base-release activity and transformed into the other. The latter Fe(III) complex was stable but inactive. By addition of hydrogen peroxide to the latter, the former was regenerated and the base-release activity appeared. Oxygen concentration measurements by oxygraph showed that 1 mole of BLM-Fe(II) consumed .apprx. 0.5 mole of O2 instantly but not any more thereafter in the absence of a reducing agent. While in the presence of 2-mercapto-ethanol, the O2 consumption proceeded biphasically and equimolar oxygen was consumed by BLM-Fe(II) in the 1st rapid reaction. Oxygen adduct of BLM-Fe(II) may be reduced by 1 electron transfer from an external electron donor and the resulting BLM-Fe(III)-O2H- [or its deprotonated form: BLM-Fe(III)-O22-] shows the activity to break DNA accompanying the base-release.