Better Model Of Methanol Enzyme

Some bacteria rely on the enzyme methane monooxygenase (MMO) to convert methane into methanol. Now, a research team led by Lawrence Que Jr. of the University of Minnesota, Minneapolis, and Eckard Münck of Carnegie Mellon University has synthesized a new diiron complex that provides a better model for studying MMO's mechanism of action (Proc. Natl. Acad. Sci. USA, DOI: 10.1073/pnas.0708516105). MMO's soluble version reacts with O₂ to yield a diiron(IV) intermediate, simply called Q, which is the species known to oxidize CH₄. Que and coworkers previously proposed that Q has a diamond-shaped Fe^IV₂O₂ core, and they synthesized an Fe^IIIFe^IVO₂ complex as a model. In the new work, the researchers were able to oxidize this complex to Fe^IV₂O₂ (shown) by electrolysis. Reactivity differences between the diiron model and an iron complex with an Fe^IV=O center provide clues to understanding MMO activity, the scientists say, in particular pointing to a mechanism in which the Fe^IV₂O₂ ring opens to form a terminal Fe^V=O unit that reacts with CH₄.