Enzyme Removes Pesticide Residue Pronto

The hydrolytic dechlorination of trans-3-chloroacrylate to malonic semialdehyde (shown) is a key step in the degradation of 1,3-dichloropropene, the active ingredient of certain commercial pesticides. The reaction is mediated by the bacterial enzyme 3-chloroacrylate dehalogenase. Were it not for this enzyme, it would take thousands of years to degrade the pesticide completely, conclude Richard V. Wolfenden and Christopher M. Horvat at the University of North Carolina, Chapel Hill. The researchers have found that the uncatalyzed reaction at 25 °C has a half-life of 10,000 years and that the enzyme accelerates the reaction rate by 10¹² (Proc. Natl. Acad. Sci. USA, published online, dx.doi.org/10.1073/pnas.0508176102). Because the pesticide was first used in 1946, the enzyme’s effectiveness is intriguing, Wolfenden says. The remarkable proficiency makes it unlikely that the enzyme is newly evolved, he explains. As others have suggested, chloroacrylate hydrolytic dechlorination may be “an accidental activity of another enzyme whose existence is not at the moment recognized,” he adds.