Resolution of the uncertainty in the kinetic mechanism for the trans -3-Chloroacrylic acid dehalogenase-catalyzed reaction

Abstract

trans- and cis-3-Chloroacrylic acid dehalogenase (CaaD and cis-CaaD, respectively) catalyze the hydrolytic dehalogenation of their respective isomers and represent key steps in the bacterial conversion of 1,3-dichloropropene to acetaldehyde. In prior work, a kinetic mechanism for the CaaD-catalyzed reaction could not be unequivocally determined because (1) the order of product release could not be determined and (2) the fluorescence factor for the enzyme species, E*PQ (where P = bromide and Q = malonate semialdehyde, the two products of the reaction) could not be assigned. The ambiguities in the model have now been resolved by stopped-flow experiments following the reaction using an active site fluorescent probe, αY60W-CaaD and 3-bromopropiolate, previously shown to be a mechanism-based inhibitor of CaaD, coupled with the rate of bromide release in the course of CaaD inactivation. A global fit of the combined datasets provides a complete minimal model for the reaction of αY60W-CaaD and 3-bromoacrylate. In addition, the global fit produces kinetic constants for CaaD inactivation by 3-bromopropiolate and implicates the acyl bromide as the inactivating species. Finally, a comparison of the model with that for cis-CaaD shows that for both enzymes turnover is limited by product release and not chemistry.

Functional Characterization of Cj1427, a Unique Ping-Pong Dehydrogenase Responsible for the Oxidation of GDP-d-glycero-α-d-manno-heptose in Campylobacter jejuni

“…The conventional analysis of the stopped-flow data and resulting minimal kinetic model were used as initial guides to fit the data by simulation using Kintek Global Kinetic Explorer. − During the process of global optimization, the data collected over a series of concentrations within a given experiment were scaled using a correction factor (<3%) for each trace to correct for lamp drift between traces.…”