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Isotope effects on the crotonase reaction
1Department of Chemistry, Brown University, Providence, Rhode Island 02912.
Biochemistry
|May 16, 1989
Summary
This study investigated the dehydration mechanism of [(3S)-3-hydroxybutyryl]pantetheine using kinetic isotope effects. Results suggest C-O bond cleavage is rate-determining, consistent with E1cb or E2 mechanisms.
Area of Science:
- Biochemistry
- Enzyme kinetics
- Organic chemistry
Background:
- Crotonase (enoyl-CoA hydratase) catalyzes the dehydration of hydroxyacyl-CoA esters.
- Understanding the enzyme's catalytic mechanism is crucial for drug design and metabolic studies.
Purpose of the Study:
- To elucidate the catalytic mechanism of bovine liver crotonase.
- To determine the rate-determining step and transition state characteristics during substrate dehydration.
Main Methods:
- Measurement of primary and secondary deuterium kinetic isotope effects (KIEs).
- Determination of primary 18O KIEs.
- Application of the equilibrium perturbation method.
Main Results:
- Primary deuterium KIE of 1.61 and 18O KIE of 1.051 were observed.
- Secondary deuterium KIEs at C-2, C-3, and C-4 were 1.12, 1.13, and 1.00, respectively.
- A significant 18O KIE indicates rate-determining C-O bond cleavage, supporting E1cb or E2 mechanisms with carbanion character.
Conclusions:
- The dehydration reaction proceeds via C-O bond cleavage as the rate-determining step.
- The transition state exhibits significant carbanion character.
- Beta-secondary KIE suggests coupling between C-H bond motion and the reaction coordinate.