title: Combined C and Cl isotope effects indicate differences between corrinoids and enzyme (Sulfurospirillum multivorans PceA) in reductive dehalogenation of tetrachloroethene, but not trichloroethene.
abstract: The role of the corrinoid cofactor in reductive dehalogenation catalysis by tetrachloroethene reductive dehalogenase (PceA) of Sulfurospirillum multivorans was investigated using isotope analysis of carbon and chlorine. Crude extracts containing PceA--harboring either a native norpseudo-B12 or the alternative nor-B12 cofactor--were applied for dehalogenation of tetrachloroethene (PCE) or trichloroethene (TCE), and compared to abiotic dehalogenation with the respective purified corrinoids (norpseudovitamin B12 and norvitamin B12), as well as several commercially available cobalamins and cobinamide. Dehalogenation of TCE resulted in a similar extent of C and Cl isotope fractionation, and in similar dual-element isotope slopes (εC/εCl) of 5.0-5.3 for PceA enzyme and 3.7-4.5 for the corrinoids. Both observations support an identical reaction mechanism. For PCE, in contrast, observed C and Cl isotope fractionation was smaller in enzymatic dehalogenation, and dual-element isotope slopes (2.2-2.8) were distinctly different compared to dehalogenation mediated by corrinoids (4.6-7.0). Remarkably, εC/εCl of PCE depended in addition on the corrinoid type: εC/εCl values of 4.6 and 5.0 for vitamin B12 and norvitamin B12 were significantly different compared to values of 6.9 and 7.0 for norpseudovitamin B12 and dicyanocobinamide. Our results therefore suggest mechanistic and/or kinetic differences in catalytic PCE dehalogenation by enzymes and different corrinoids, whereas such differences were not observed for TCE.
authors.affiliation: Department for Isotope Biogeochemistry, Helmholtz-Centre for Environmental Research - UFZ , Permoserstrasse 15, D-04318 Leipzig, Germany.
authors.forename: Julian
authors.initials: J
authors.lastname: Renpenning
authors.forename: Sebastian
authors.initials: S
authors.lastname: Keller
authors.forename: Stefan
authors.initials: S
authors.lastname: Cretnik
authors.forename: Orfan
authors.initials: O
authors.lastname: Shouakar-Stash
authors.forename: Martin
authors.initials: M
authors.lastname: Elsner
authors.forename: Torsten
authors.initials: T
authors.lastname: Schubert
authors.forename: Ivonne
authors.initials: I
authors.lastname: Nijenhuis
mesh_terms: D002247:Carbon Isotopes; D005591:Chemical Fractionation; D002713:Chlorine / Q000032:analysis*; D045728:Corrinoids / Q000737:chemistry / Q000378:metabolism*; D020565:Epsilonproteobacteria / Q000201:enzymology*; D054879:Halogenation; D006867:Hydrolases / Q000378:metabolism*; D007553:Isotope Labeling; D013750:Tetrachloroethylene / Q000378:metabolism*; D014241:Trichloroethylene / Q000378:metabolism*
chemical_list: D002247:Carbon Isotopes; D045728:Corrinoids; D014241:Trichloroethylene; D002713:Chlorine; D006867:Hydrolases; D013750:Tetrachloroethylene