D-specific dehalogenases, a review

Bacterial dehalogenases cleave carbon-halogen bonds with different stereo-configurations. Rhizobium sp. RC1 produces a D-haloalkanoic-specific dehalogenase (DehD) that can cleave the carbon-halogen bond of halogenated organic pollutants. The sequence identity for DehD and HadD from Pseudomonas putida AJ1 is 27%, and 20 amino acid residues are highly conserved in these two enzymes. Therefore, DehD and HadD may have active sites that contain the same charged catalytic residues. The activity of DehD rapidly increases with increasing pH and is optimum at pH 9.5. It also has lower Km values and higher kcat values for various substrates than do other D-specific dehalogenases. Because DehD catalyzes the hydrolytic dehalogenation of D-haloalkanoic acids with inversion around the chiral carbon, it has potential industrial applications. Site-directed mutagenesis of DehD can be exploited for industrial production of chemicals, pharmaceutical and medical applications, and in environmental remediation

Degradation of millimolar concentration of the herbicide dalapon (2,2-Dichloropropionic Acid) by rhizobium Sp isolated from soil

The herbicide Dalapon is widely used in agricultural areas and is persistent in ground water. A Rhizobium sp. was able to grow at 0.2 mM 2,2-dichloropropionic acid (2,2DCP), which was 100-fold lower than the concentration of the substrate routinely used. Apparently, no new dehalogenases are required to allow growth on this low concentration of 2,2DCP as judged by electrophoretic mobility of dehalogenase proteins in native-PAGE analysis and protein separation by anion-exchange column chromatography. The kinetic analysis suggested that the known dehalogenases were able to act efficiently on low concentrations of haloalkanoic acids. The amount of each dehalogenase, from cells grown on low substrate concentration was different compared to that seen at 20 mM 2,2DCP due to complex regulatory controls, which respond to the growth environment