Cytochrome dioxygen bond cleavage

A less common reactive species is the Fe peroxo anion expected from two-electron reduction of O2 at a hemoprotein iron atom (Fig. 14, structure A). Protonation of this intermediate would yield the Fe —OOH precursor (Fig. 14, structure B) of the ferryl species. However, it is now clear that the Fe peroxo anion can directly react as a nucleophile with highly electrophilic substrates such as aldehydes. Addition of the peroxo anion to the aldehyde, followed by homolytic scission of the dioxygen bond, is now accepted as the mechanism for the carbon-carbon bond cleavage reactions catalyzed by several cytochrome P450 enzymes, including aromatase, lanosterol 14-demethylase, and sterol 17-lyase (133). A similar nucleophilic addition of the Fe peroxo anion to a carbon-nitrogen double bond has been invoked in the mechanism of the nitric oxide synthases (133). 

Proshlyakov, D. A., Pressler, M. A., and Babcock, G. T., 1998, Dioxygen activation and bond cleavage by mixed-valence cytochrome c oxidase Proc. Natl. Acad. Sci. U. S. A. 95 8020n8025. 

The mechanism proposed for the 4-electron reduction of dioxygen to water by cytochrome c oxidase may be similar to that proposed for the monoxygenase enzymes, the cytochromes P450, as well as the peroxidases and catalase, all of which are discussed iu Sectiou 9 below. DFT calculations of the mechanism of the bond cleavage step, specifically addressing CcO, have been reported and an excellent overview provided. ... 

As mentioned above, much less is known about the structural characteristics and mechanisms of the nonheme metal-containing monooxygenase enzymes. From the similarities of the overall stoichiometries of the reactions and the resemblance of some of the enzymes to dioxygen-binding proteins, it is likely that the initial steps are the same as those for cytochrome P-450, i.e., dioxygen binding followed by reduction to form metal-peroxide or hydroperoxide complexes. It is not obvious that the next step is the same, however (i.e., O—O bond cleavage... 

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