Chlorinated ethene reactivity with vitamin B12 is governed by cobalamin chloroethylcarbanions as crossroads of competing pathways.
ACS Catal. 8, 3054-3066 (2018)
Chlorinated ethenes are toxic groundwater contaminants. Although they can be dechlorinated by microorganisms, reductive dehalogenases, and their corrinoid cofactor, biochemical reaction mechanisms remain unsolved. This study uncovers a mechanistic shift revealed by contrasting compound-specific carbon (ϵ13C) and chlorine (ϵ37Cl) isotope effects between perchloroethene, PCE (ϵ37Cl = -4.0‰) and cis-dichloroethene, cis-DCE (ϵ37Cl = -1.5‰), and a pH-dependent shift for trichloroethene, TCE (from ϵ37Cl = -5.2‰ at pH 12 to ϵ37Cl = -1.2‰ at pH 5). Different pathways are supported also by pH-dependent reaction rates, TCE product distribution, and hydrogen isotope effects. Mass balance deficits revealed reversible and irreversible cobalamin-substrate association, whereas high-resolution mass spectrometry narrowed down possible structures to chloroalkyl and chlorovinyl cobalamin complexes. Combined experimental evidence is inconsistent with initial electron transfer or alkyl or vinyl complexes as shared intermediates of both pathways. In contrast, it supports cobalamin chlorocarbanions as key intermediates from which Cl-elimination produces vinyl complexes (explaining rates and products of TCE at high pH), whereas protonation generates less reactive alkyl complexes (explaining rates and products of TCE at low pH). Multielement isotope effect analysis holds promise to identify these competing mechanisms also in real dehalogenases, microorganisms, and even contaminated aquifers.
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Publikationstyp Artikel: Journalartikel
Schlagwörter Chlorinated Ethenes ; Cobalamin ; Groundwater Contamination ; Kinetic Isotope Effect ; Mechanistic Study ; Outer-sphere Single-electron Transfer ; Reductive Dehalogenation ; Trichloroethene; Randomized Controlled-trial; Chronic Tic Disorders; Parkinsons-disease; Health-care; Tourette-syndrome; Behavior-therapy; Neurological Disorders; Huntington Disease; Batten-disease; Virtual Visits
ISSN (print) / ISBN 2155-5435
Zeitschrift ACS catalysis
Quellenangaben Band: 8, Heft: 4, Seiten: 3054-3066
Verlagsort Washington, DC
Institut(e) Institute of Groundwater Ecology (IGOE)