Dehydrochlorination is one of the main (thus far discovered) processes for aerobic microbial transformation of hexachlorocyclohexane (HCH) which is mainly catalyzed by LinA enzymes. In order to gain a better understanding of the reaction mechanisms, multi-element compound-specific stable isotope analysis was applied for evaluating α- and γ-HCH transformations catalyzed by LinA1 and LinA2 enzymes. The isotopic fractionation (εE) values for particular elements of (+)α-HCH (εC = -10.8 ± 1.0‰, εCl = -4.2 ± 0.5‰, εH = -154 ± 16‰) were distinct from the values for (-)α-HCH (εC = -4.1 ± 0.7‰, εCl = -1.6 ± 0.2‰, εH = -68 ± 10‰), whereas the dual-isotope fractionation patterns were almost identical for both enantiomers (ΛC-Cl = 2.4 ± 0.4 and 2.5 ± 0.2, ΛH-C = 12.9 ± 2.4 and 14.9 ± 1.1). The εE of γ-HCH transformation by LinA1 and LinA2 were -7.8 ± 1.0‰ and -7.5 ± 0.8‰ (εC), -2.7 ± 0.3‰ and -2.5 ± 0.4‰ (εCl), -170 ± 25‰ and -150 ± 13‰ (εH), respectively. Similar ΛC-Cl values (2.7 ± 0.2 and 2.9 ± 0.2) were observed as well as similar ΛH-C values (20.1 ± 2.0 and 18.4 ± 1.9), indicating a similar reaction mechanism by both enzymes during γ-HCH transformation. This is the first data set on 3D isotope fractionation of α- and γ-HCH enzymatic dehydrochlorination, which gave a more precise characterization of the bond cleavages, highlighting the potential of multi-element compound-specific stable isotope analysis to characterize different transformation processes (e.g., dehydrochlorination and reductive dehalogenation).
Keywords: LinA enzymes; dehydrochlorination; isotope fractionation; pesticides; transformation.