Two-step concerted mechanism for methane hydroxylation on the diiron active site of soluble methane monooxygenase.
A new concerted mechanism is proposed for the conversion of methane to methanol on intermediate Q of soluble methane monooxygenase (sMMO), the active site of which is considered to involve an Fe2(mu-O)2 diamond core. A hybrid density functional theory (DFT) method is used for our mechanistic study on the important reactivity of the bare FeO+ complex and a diiron model of intermediate Q. The reaction pathway for the methane hydroxylation on the diiron complex is essentially identical to that for the gas-phase reaction by the bare FeO+ complex. Methane is highly activated on the dinuclear iron model through the formation of a methane complex, in which a coordinatively unsaturated iron plays a central role in the bonding interaction between the diiron model and substrate methane. A H atom abstraction via a four-centered transition state and a recombination of the OH and CH3 groups via a three-centered transition state successively occur on the dinuclear iron-oxo species, leading to the formation of a methanol complex that corresponds to intermediate T. These electronic processes take place in a concerted manner. Our mechanism for methane hydroxylation by sMMO is different from the radical mechanism that has been widely accepted for enzymatic hydrocarbon hydroxylation, especially by cytochrome P450.
Yoshizawa
K
K
Department of Molecular Engineering, Kyoto University, Japan. kazunari@scl.kyoto-u.ac.jp
D001665:Binding Sites; D002384:Catalysis; D006900:Hydroxylation; D007501:Iron / Q000378:metabolism*; D008697:Methane / Q000378:metabolism*; D000432:Methanol / Q000378:metabolism; D008958:Models, Molecular; D009097:Multienzyme Complexes; D019159:Nonheme Iron Proteins / Q000737:chemistry / Q000378:metabolism; D010105:Oxygenases / Q000737:chemistry* / Q000378:metabolism*; D012995:Solubility; D013816:Thermodynamics
D009097:Multienzyme Complexes; D019159:Nonheme Iron Proteins; D007501:Iron; D010105:Oxygenases; C021555:methane monooxygenase; D008697:Methane; D000432:Methanol