Formation of C₁/C₂-bromo-/chloro-hydrocarbons by haloperoxidase reactions

Summary

We report here the first results of a study of the enzymatic formation of halogenated C₁/C₂-hydrocarbons from natural, biochemically relevant molecules using enzymes such as chloroperoxidase (CPO) or horseradish peroxidase (HRP). As halogen sources KBr, NaCl or a sea salt solution were utilized. The haloform reaction was used as a subsequent reaction to yield the halogenated methanes and ethanes from the halogenated substrate molecules. The products of the incubations were analyzed by HRGC/ECD. With these in vitro reactions we attempted to investigate possible biochemical pathways for the formation of some volatile halogenated organic compounds which are assumed to be of biogenic origin. Most of the incubations with KBr formed bromoform as the main product together with dibromo-chloro-methane and 1,1,2,2-tetrachloroethane as by-products. Incubations with NaCl result in chloroform as the main product in analogy to the formation of bromoform. The reaction with sea salt yields no major product but a spectrum of halogenated C₁/C₂-hydrocarbons. Incubations of a water extract of algae meal without any further source of Cl⁻/Br⁻-ions yield CHCl₃ as the main product and other mixed halogenated methanes as side products. Blank reactions were carried out without enzyme, H₂O₂ or substrate to show that the products of the incubations are formed enzymatically and to exclude the possibility of normal hypohalogenic reactions of the halide, H₂O₂ and the substrate.