OXYGEN-EXCHANGE WITH WATER IN HEME-OXO INTERMEDIATES DURING H2O2-DRIVEN OXYGEN INCORPORATION IN AROMATIC-HYDROCARBONS CATALYZED BY MICROPEROXIDASE-8

The present paper describes the oxygen incorporation into naphthalene and anthracene by H2O2- driven microperoxidase-8, forming alpha-naphth ol and anthraquinone, respectively. Microperoxidase-8 is a minienzyme containing a histidinyl-coordinated Fe3+-protoporphyrin IX cofactor co valently attached to an eight-amino-acid peptide. Additional experimen ts were performed to investigate whether the reaction mechanism involv ed is like that of peroxidase and/or cytochrome P-450. A reaction path way like that of cytochrome P-450 implies oxygen transfer to the subst rate from the as yet uncharacterized iron-ore species formed in the re action of the heme cofactor with H2O2. In contrast, a peroxidase-type reaction chemistry involves reaction pathways proceeding by initial on e-electron oxidation of, or H-abstraction from, the substrate, followe d by incorporation of oxygen from sources other than the iron-ore spec ies, i.e. from other than H2O2. The results of the present study exclu de Fenton-type chemistry and prove that the minicatalyst is able to ca talyze the oxygen incorporation by both peroxidase and cytochrome P-45 0 types of reaction pathways, while exchange occurs between the high-v alency iron-ore species and H2O. The mechanistic implications of this exchange for cytochrome P-450 are discussed.