Paper
A Concerted Mechanism for Ethane Hydroxylation by the Particulate Methane Monooxygenase from Methylococcus capsulatus (Bath)
Published Jan 31, 1996 · B. Wilkinson, Mei Zhu, N. Priestley
Journal of the American Chemical Society
71
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0
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Abstract
The ethanol samples in the isolated alcohol/water mixtures were converted into their (2R)-2-acetoxy-2-phenylethanoate derivatives (2-34 mCi). Examination of the well-resolved {sup 3}H NMR spectra for these derivatives produced an exceptionally consistent set of stereochemical data. When corrected for the enantiomeric purity of the ethyl tosylate starting materials, the data clearly show that the reaction occurs with complete retention of configuration, i.e., with 100% stereoselection. Barring substantial slowing of the carbon-carbon bond rotation of the ethyl radical when bound to the enzyme, this result rules out mechanisms proceeding via alkyl radical (and/or cation) structures, even very short-lived ones, as such intermediates would have to have a lifetime of < 1 x 10{sup -14} s in order not to undergo any detectable C-C bond rotation, i.e., the capture reaction would have to be much faster than the decay of a transition state. The data instead point to a mechanism in which C-H bond cleavage is preceded by bond formation at the alkyl carbon, i.e., one proceeding through a pentacoordinated carbon species. 29 refs., 1 fig., 1 tab.
Highly CitedThe Particulate Methane Monooxygenase from Methylococcus capsulatus completes ethanol hydroxylation with complete retention of configuration, indicating a mechanism in which C-H bond cleavage is preceded by bond formation at the alkyl carbon.
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