REDUCTIVE DECHLORINATION OF TETRACHLOROETHENE TO ETHENE BY 2-COMPONENT ENZYME PATHWAY

Two membrane-bound, reductive dehalogenases that constitute a novel pa thway for complete dechlorination of tetrachloroethene (perchloroethyl ene [PCE]) to ethene were partially purified from an anaerobic microbi al enrichment culture containing Dehalococcoides ethenogenes 195. When titanium(III) citrate and methyl viologen were used as reductants, PC E-reductive dehalogenase (PCE-RDase) (51-kDa) dechlorinated PCE to tri chloroethene (TCE) at a rate of 20 mu mol/min/mg of protein. TCE-reduc tive dehalogenase (TCE-RDase) (61 kDa) dechlorinated TCE to ethene. TC E, cis-1,2-dichloroethene, and 1,1-dichloroethene were dechlorinated a t similar rates, 8 to 12 mu mol/min/mg of protein. Vinyl chloride and trans-1,2-dichloroethene were degraded at rates which were approximate ly 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 bac terial enzymes provided further insight into the catalytic mechanisms of biological reductive dehalogenation.