Contrasting Kinetics\nof Highly Similar Chloroalkane\nReductive Dehalogenases

Chloroform and trichloroethanes are pervasive groundwater\ncontaminants\nfor which bioremediation has been an effective treatment strategy.\nReductive dehalogenase (RDase) enzymes from organohalide-respiring\nbacteria are essential for their remediation under anaerobic conditions.\nRDases are responsible for dehalogenating these chlorinated solvents,\nleading to their removal. This work explores the kinetic characteristics\nof three closely related <i>Dehalobacter</i> chloroalkane-reductasesTmrA,\nCfrA, and AcdAand identifies differences between their activity\non chloroform (CF), 1,1,1-trichloroethane (TCA), and 1,1,2-TCA. The\nside-by-side comparison of these enzymes has emphasized that TmrA\nand AcdA are specialized toward CF with both having a 4-fold higher\nmaximum specific activity (<i>V</i><sub>max</sub>) on CF\nthan 1,1,1-TCA, whereas CfrA has very similar rates on both CF and\n1,1,1-TCA. AcdA is the most sensitive to substrate inhibition by CF\nand 1,1,2-TCA and inhibition by a common cocontaminant trichloroethene.\nFinally, the reduction of 1,1,2-TCA, which can produce both 1,2-dichloroethane\nand vinyl chloride, was assessed for each enzyme. Interestingly, each\nenzyme has a distinct preference for the major product it produces,\nindicating a favored reaction pathway. Despite over 95% sequence identity,\nTmrA, CfrA, and AcdA exhibit substantial differences in kinetic behavior,\nhighlighting the importance of understanding such nuances for informed\nbioremediation strategies.