Isotope effects on the crotonase reaction.
The primary, alpha-secondary, beta-secondary, and beta'-secondary deuterium and primary 18O kinetic isotope effects on V/K for the dehydration of [(3S)-3-hydroxybutyryl]pantetheine by bovine liver crotonase (enoyl-CoA hydratase, EC 4.2.1.17) have been determined by the equilibrium perturbation method. The primary deuterium and 18O kinetic isotope effects are 1.61 and 1.051, respectively. The secondary deuterium effects at C-2, C-3, and C-4 are 1.12, 1.13, and 1.00 per H, respectively. The large 18O isotope effect suggests C-O bond cleavage is largely rate determining but is consistent with either an E1cb or E2 mechanism with a large amount of carbanion character. The beta-secondary effect is a factor of 1.05 greater than the equilibrium isotope effect, indicating that this C-H bond is less stiff in the affected transition state or that its motion is coupled to the reaction coordinate motion. Analytical solutions to the differential equations describing uni-uni equilibrium perturbations are presented.
Department of Chemistry, Brown University, Providence, Rhode Island 02912.
B J
BJ
Bahnson
V E
VE
Anderson
D000818:Animals; D002417:Cattle; D003903:Deuterium; D004746:Enoyl-CoA Hydratase / Q000378:metabolism*; D006836:Hydro-Lyases / Q000378:metabolism*; D066298:In Vitro Techniques; D007700:Kinetics; D008099:Liver / Q000201:enzymology; D008956:Models, Chemical; D010103:Oxygen Isotopes; D010204:Pantetheine / Q000031:analogs & derivatives
D010103:Oxygen Isotopes; D010204:Pantetheine; D003903:Deuterium; D006836:Hydro-Lyases; D004746:Enoyl-CoA Hydratase