Substrate-dependent hysteretic behavior in StEH1-catalyzed hydrolysis of styrene oxide derivatives
2008 (English)In: The FEBS Journal, ISSN 1742-464X, Vol. 275, no 24, 6309-6320 p.Article in journal (Refereed) Published
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 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 2.9, respectively. Monitoring of the pre-steady-state phase of the reaction with (S,S)-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 (S,S)-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 intermediates by StEH1 are important for enantioselectivity with styrene oxide or trans-stilbene oxide as substrate. With 2-methylstyrene oxide, slow conformational changes in the enzyme also influence the catalytic efficiency.
Place, publisher, year, edition, pages
2008. Vol. 275, no 24, 6309-6320 p.
IdentifiersURN: urn:nbn:se:uu:diva-86664DOI: 10.1111/j.1742-4658.2008.06754.xISI: 000261184700025OAI: oai:DiVA.org:uu-86664DiVA: diva2:126842