Reductive Dechlorination of Tetrachloroethene to Ethene by a Two-Component Enzyme Pathway

Two membrane-bound, reductive dehalogenases that constitute a novel pathway for complete dechlorination of tetrachloroethene (perchloroethylene [PCE]) to ethene were partially purified from an anaerobic microbial enrichment culture containing Dehalococcoides ethenogenes 195. When titanium(III) citrate and methyl viologen were used as reductants, PCE-reductive dehalogenase (PCE-RDase) (51 kDa) dechlorinated PCE to trichloroethene (TCE) at a rate of 20 μmol/min/mg of protein. TCE-reductive dehalogenase (TCE-RDase) (61 kDa) dechlorinated TCE to ethene. TCE, cis-1,2-dichloroethene, and 1,1-dichloroethene were dechlorinated at similar rates, 8 to 12 μmol/min/mg of protein. Vinyl chloride and trans-1,2-dichloroethene were degraded at rates which were approximately 2 orders of magnitude lower. The light-reversible inhibition of TCE-RDase by iodopropane and the light-reversible inhibition of PCE-RDase by iodoethane suggest that both of these dehalogenases contain Co(I) corrinoid cofactors. Isolation and characterization of these novel bacterial enzymes provided further insight into the catalytic mechanisms of biological reductive dehalogenation.