Transformation of polychlorinated biphenyls with oxidative enzymes

Enzymatic transformation of different PCB congeners was studied using two oxidative enzymes, horseradish peroxidase and cytochrome c. The optimum pH and hydrogen peroxide concentration for the maximum catalytic efficiency of the enzymes were pH 4.0 to 6.0 and 0.5 to 1.0 mM, respectively. There was a rapid initial catalysis phase during the first 6 h and then the reaction rate slowed down. Addition of polyethylene glycol at low concentrations (50-100 ppm) to the reaction mixture had a significant protective effect on the activity of both enzymes and enhanced the transformation rate. Di-, tetra- and hexa-chlorinated biphenyls were better substrates as compared to tri- and penta-chlorinated biphenyls for horseradish peroxidase. Cytochrome c exhibited preference for lower chlorinated congeners. Under optimum conditions the transformation efficiency of horseradish peroxidase and cytochrome c was 60-80% and 66-93%, respectively, depending on the congener.