title: Substrate and Enzyme Specificity of the Kinetic Isotope Effects Associated with the Dioxygenation of Nitroaromatic Contaminants.
abstract: Compound-specific isotope analysis (CSIA) is a promising approach for tracking biotransformation of organic pollutants, but isotope fractionation associated with aromatic oxygenations is only poorly understood. We investigated the dioxygenation of a series of nitroaromatic compounds to the corresponding catechols by two enzymes, namely, nitrobenzene and 2-nitrotoluene dioxygenase (NBDO and 2NTDO) to elucidate the enzyme- and substrate-specificity of C and H isotope fractionation. While the apparent (13)C- and (2)H-kinetic isotope effects of nitrobenzene, nitrotoluene isomers, 2,6-dinitrotoluene, and naphthalene dioxygenation by NBDO varied considerably, the correlation of C and H isotope fractionation revealed a common mechanism for nitrobenzene and nitrotoluenes. Similar observations were made for the dioxygenation of these substrates by 2NTDO. Evaluation of reaction kinetics, isotope effects, and commitment-to-catalysis based on experiment and theory showed that rates of dioxygenation are determined by the enzymatic O2 activation and aromatic C oxygenation. The contribution of enzymatic O2 activation to the reaction rate varies for different nitroaromatic substrates of NBDO and 2NTDO. Because aromatic dioxygenation by nonheme iron dioxygenases is frequently the initial step of biodegradation, O2 activation kinetics may also have been responsible for the minor isotope fractionation reported for the oxygenation of other aromatic contaminants.
authors.affiliation: Eawag, Swiss Federal Institute of Aquatic Science and Technology, 8600 Dübendorf, Switzerland.|Institute of Biogeochemistry and Pollutant Dynamics (IBP), ETH Zürich , 8092 Zürich, Switzerland.
authors.forename: Sarah G
authors.initials: SG
authors.lastname: Pati
authors.affiliation: Eawag, Swiss Federal Institute of Aquatic Science and Technology, 8600 Dübendorf, Switzerland.
authors.forename: Hans-Peter E
authors.initials: HP
authors.lastname: Kohler
authors.affiliation: Institute of Applied Radiation Chemistry, Lodz University of Technology , 90-924 Lodz, Poland.
authors.forename: Anna
authors.initials: A
authors.lastname: Pabis
authors.affiliation: Institute of Applied Radiation Chemistry, Lodz University of Technology , 90-924 Lodz, Poland.
authors.forename: Piotr
authors.initials: P
authors.lastname: Paneth
authors.affiliation: Department of Microbiology and Molecular Genetics, University of California , Davis, California 95616, United States.
authors.forename: Rebecca E
authors.initials: RE
authors.lastname: Parales
authors.affiliation: Eawag, Swiss Federal Institute of Aquatic Science and Technology, 8600 Dübendorf, Switzerland.|Institute of Biogeochemistry and Pollutant Dynamics (IBP), ETH Zürich , 8092 Zürich, Switzerland.
authors.forename: Thomas B
authors.initials: TB
authors.lastname: Hofstetter
mesh_terms: D001673:Biodegradation, Environmental; D002247:Carbon Isotopes; D049308:Dioxygenases / Q000378:metabolism*; D007700:Kinetics; D009587:Nitrogen Isotopes; D013379:Substrate Specificity
chemical_list: D002247:Carbon Isotopes; D009587:Nitrogen Isotopes; D049308:Dioxygenases