Peroxidase dioxygen bond cleavage

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. ... 

Fig. 4.78. Role of the distal histidine in the "pull" mechanism for the cleavage of the dioxygen bond and creation of the high-valent iron-oxo porphyrin it cation radical (Compound I) in peroxidases.

Oxoiron(IV) porphyrins, one oxidizing equivalent above the resting ferric state, are known as compound II in the catalytic cycle of peroxidases and catalases. The (Porp)Fe =0 complexes can be generated by (i) the homolytic O—O bond cleavage of (Porp)Fe -0-0-Fe (Porp), which is formed by the addition of dioxygen to iron(II) porphyrins in the presence of a nitrogen base, (ii) the chemical oxidation of iron(III) porphyrins by m-CPBA and PhIO under certain circumstances, (iii) the electrochemical oxidation of hydroxoiron(III) porphyrins, and (iv) the reactions of iron(III) porphyrins with hydroperoxides (ROOH) in aqueous or organic solvents. More detailed preparation methods and physical properties of various oxoiron(IV) porphyrin complexes are summarized in recent reviews. ... 

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