DETERMINATION OF THE GEOMETRIC AND ELECTRONIC-STRUCTURE OF ACTIVATED BLEOMYCIN USING X-RAY-ABSORPTION SPECTROSCOPY

Activated Bleomycin (BLM) is the first mononuclear non-heme iron oxygen intermediate stable enough for detailed spectroscopic study. DNA degradation by activated BLM involves C-H bond:cleavage at the C4' position of deoxyribose moieties and results in the production of base propenals.::It has been postulated that activated BLM is an oxo-ferryl intermediate on the basis of its reactivity and analogy With cytochrome P-450 chemistry. Alternatively, spectroscopic and model studies have indicated activated BLM to have an iron(III)-peroxide site. In this study, X-ray absorption spectroscopy (XAS) has been used to directly probe the oxidation and spin states of the iron in activated BLM and to determine if a short iron-ore bond is present, which would be characteristic of the oro-ferryl species of heme iron. Both the pre-edge and edge regions of the:Ee K-edge spectra indicate that activated BLM is a low spin ferric complex, The pre-edge intensity of activated BLM is also similar to that of low spin ferric BLM and does not show the intensity enhancement which would be present if there were a short Fe-O bond. Furthermore, bond distances obtained from EXAFS are similar to those in low spin Fen(III)BLM and show no evidence for a short iron-ore bond. These data indicate that activated BLM is a peroxy-low spin ferric complex and suggest that such an intermediate may play an important role in activating O-2 for further chemistry in the catalytic cycles of mononuclear non-heme iron enzymes.