title: Reactions of the diiron(IV) intermediate Q in soluble methane monooxygenase with fluoromethanes.
abstract: Soluble methane monooxygenases utilize a carboxylate-bridged diiron center and dioxygen to convert methane to methanol. A diiron(IV) oxo intermediate Q is the active species for this process. Alternative substrates and theoretical studies can help elucidate the mechanism. Experimental results for reactions with derivatized methanes were previously modeled by a combination of quantum mechanical/molecular mechanical techniques and the model was extended to predict the relative reactivity of fluoromethane. We therefore studied reactions of Q with CF(n)H(4-n) (n=1-3) to test the prediction. The kinetics of single-turnover reactions of Q with these substrates were monitored by double-mixing stopped-flow optical spectroscopy. For fluoro- and difluoromethane, conversion to the alcohols occurred with second-order rate constants less than that of methane, the values being 28,700 (CH4)>25,000 (CFH3)>9300 (CF2H2) M(-1) s(-1). KIE values for C-H versus C-D activation above the classical limit were observed, requiring modification of the theoretical predictions.
authors.affiliation: Department of Chemistry, Massachusetts Institute of Technology, Cambridge, MA 02139, USA.
authors.forename: Laurance G
authors.initials: LG
authors.lastname: Beauvais
authors.forename: Stephen J
authors.initials: SJ
authors.lastname: Lippard
mesh_terms: D002384:Catalysis; D006845:Hydrocarbons, Fluorinated / Q000737:chemistry / Q000378:metabolism*; D009682:Magnetic Resonance Spectroscopy; D008697:Methane / Q000378:metabolism*; D000432:Methanol / Q000378:metabolism; D020619:Methylococcus capsulatus / Q000201:enzymology; D020602:Methylosinus trichosporium / Q000201:enzymology; D010105:Oxygenases / Q000737:chemistry / Q000502:physiology*
chemical_list: D006845:Hydrocarbons, Fluorinated; C029999:fluoromethane; D010105:Oxygenases; C021555:methane monooxygenase; D008697:Methane; D000432:Methanol