Determination of the Chlorine Kinetic Isotope Effect on the 4-Chlorobenzoyl-CoA Dehalogenase-Catalyzed Nucleophilic Aromatic Substitution

The chlorine kinetic isotope effect (KIE) on the dehalogenation of 4-chlorobenzoyl-CoA catalyzed by 4-chlorobenzoyl-CoA dehalogenase has been measured at room temperature and optimal pH. The measured value of 37k = 1.0090 ± 0.0006 is larger than the KIEs recently measured for haloalkane and fluoroacetate dehalogenase. This indicates that the transition state for dissociation of chloride ion from the Meisenheimer intermediate is sensitive to the chlorine isotopic substitution. Simple modeling suggests that this sensitivity originates in the high isotopic sensitivity of the CCl bond bending modes.