TAILIEUCHUNG - Báo cáo khoa học: Substrate-dependent hysteretic behavior in StEH1-catalyzed hydrolysis of styrene oxide derivatives

The substrate selectivity and enantioselectivity of Solanum tuberosum epoxide hydrolase 1 (StEH1) have been explored by steady-state and pre-steady-state measurements on a series of styrene oxide derivatives. A prefer-ence for the (S)- or (S,S)-enantiomers of styrene oxide, 2-methylstyrene oxide andtrans-stilbene oxide was established, with E-values of 43, 160 and , respectively. | ỊFEBS Journal Substrate-dependent hysteretic behavior in StEHI-catalyzed hydrolysis of styrene oxide derivatives Diana Lindberg Adolf Gogoll and Mikael Widersten Department of Biochemistry and Organic Chemistry Uppsala University Sweden Keywords epoxide hydrolase kinetic mechanism presteady state regiospecificity styrene oxide Correspondence M. Widersten Box 576 SE-751 23 Uppsala Sweden Fax 46 0 18 55 8431 Tel 46 0 18 471 4992 E-mail Website http Received 12 September 2008 revised 20 October 2008 accepted 22 October 2008 doi The substrate selectivity and enantioselectivity of Solanum tuberosum epoxide hydrolase 1 StEHl have been explored by steady-state and presteady-state measurements on a series of styrene oxide derivatives. A preference for the S - or S S -enantiomers of styrene oxide 2-methylstyrene oxide and trans-stilbene oxide was established with E-values of 43 160 and respectively. Monitoring of the pre-steady-state phase of the reaction with -2-methylstyrene oxide revealed two observed rates for alkylenzyme formation. The slower of these rates showed a negative substrate concentration dependence as did the rate of alkylenzyme formation in the reaction with the R R -enantiomer. Such kinetic behavior is indicative of an additional off-pathway step in the mechanism referred to as hysteresis. On the basis of these data a kinetic mechanism that explains the kinetic behavior with all tested substrates transformed by this enzyme is proposed. Regioselectivity of StEH1 in the catalyzed hydrolysis of 2-methylstyrene oxide was determined by 13C-NMR spectroscopy of 18O-labeled diol products. The -enantiomer is attacked exclusively at the C-1 epoxide carbon whereas the R R -enantiomer is attacked at either position at a ratio of 65 35 in favor of the C-1 carbon. On the basis of the results we conclude that differences in efficiency in stabilization of the alkylenzyme .

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