Methane monooxygenase (MMO) catalyzes the oxidation of stable hydrocarbons that are not attacked by cytochrome P450 monooxygenase. A key transient intermediate in the catalytic cycle of the soluble form of MMO termed compound Q (Q) has been trapped and characterized through spectroscopic comparisons with novel high valent model complexes. Q appears to contain a non-heme dinuclear Fe(IV) cluster bridged by at least two single oxygen atoms to form a so-called diamond core. Q has the ability to react directly with unactivated hydrocarbons to yield oxidized products. Several types of experiments indicate that this reaction involves formation of an intermediate, probably with radical character. This is consistent with a hydrogen atom abstraction mechanism analogous to that ascribed to cytochrome P450. However, these same experiments show that a pure hydrogen atom abstraction mechanism is unlikely for many substrates without an additional interaction between the intermediate that is formed and the high valent cluster. The results may be of general relevance to monooxygenase catalysis.
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Acknowledgements The authors wish to acknowledge the dedicated work of many students, postdoctoral fellows, and collaborators that has made the studies described here possible. This work was supported by NIH Grants GM-40466 (J.D.L.) and GM-38767 (L.Q.) as well as NSF Grant MCB-9405723 (L.Q.).
- Compound Q
- Model complexes
- Monooxygenase mechanism
- Oxygen activation