Metal-dioxygen complexes, monooxygenase

The irreversible coordination of dioxygen to metal complexes is of remarkable importance in order to explain the activity of enzymes such monooxygenases, dioxygenases and cytochrome c oxidase. 

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... 

Biochemists have been interested in the unique mechanism of the reductive dioxygen activation by monooxygenase since such a unique type of oxidation has never been found in the field of chemistry [3]. However, the biological system is so complicated as to clarify the mechanism in detail. The elucidation of the mechanisms has also attracted attention of physical organic and inorganic chemists. Chemists have applied model studies using synthetic metal complexes such as metalloporphyrins and nonheme metal complexes, and have obtained an insight into the enzymatic reaction mechanisms and the structures of the active species in the catalytic cycles [4-8]. 

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