College of Light Industry and Food Engineering, Guangxi Key Laboratory of Clean Pulp & Papermaking and Pollution Control, Guangxi University, Daxue Road 100, Nanning530004, P.R. China.
Department of Isotope Biogeochemistry, Helmholtz Centre for Environmental Research-UFZ, Permoserstraße 15, Leipzig04318, Germany.
Environ Sci Technol. 2022 Dec 6;56(23):16848-16856. doi: 10.1021/acs.est.2c05334. Epub 2022 Nov 17.
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 (ε) values for particular elements of (+)α-HCH (ε = -10.8 ± 1.0‰, ε = -4.2 ± 0.5‰, ε = -154 ± 16‰) were distinct from the values for (-)α-HCH (ε = -4.1 ± 0.7‰, ε = -1.6 ± 0.2‰, ε = -68 ± 10‰), whereas the dual-isotope fractionation patterns were almost identical for both enantiomers (Λ = 2.4 ± 0.4 and 2.5 ± 0.2, Λ = 12.9 ± 2.4 and 14.9 ± 1.1). The ε of γ-HCH transformation by LinA1 and LinA2 were -7.8 ± 1.0‰ and -7.5 ± 0.8‰ (ε), -2.7 ± 0.3‰ and -2.5 ± 0.4‰ (ε), -170 ± 25‰ and -150 ± 13‰ (ε), respectively. Similar Λ values (2.7 ± 0.2 and 2.9 ± 0.2) were observed as well as similar Λ 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).
脱氯化氢是己六氯环己烷（HCH）有氧微生物转化的主要（迄今为止发现的）过程之一，主要由 LinA 酶催化。为了更好地理解反应机制，应用多元素化合物特异性稳定同位素分析来评估 LinA1 和 LinA2 酶催化的α-和γ-HCH 转化。（+）α-HCH 的特定元素的同位素分馏（ε）值（ε=-10.8±1.0‰，ε=-4.2±0.5‰，ε=-154±16‰）与（-）α-HCH 的值明显不同（ε=-4.1±0.7‰，ε=-1.6±0.2‰，ε=-68±10‰），而两种对映体的双同位素分馏模式几乎相同（Λ=2.4±0.4 和 2.5±0.2，Λ=12.9±2.4 和 14.9±1.1）。LinA1 和 LinA2 催化的γ-HCH 转化的 ε 值分别为-7.8±1.0‰和-7.5±0.8‰（ε），-2.7±0.3‰和-2.5±0.4‰（ε），-170±25‰和-150±13‰（ε）。也观察到类似的 Λ 值（2.7±0.2 和 2.9±0.2）和类似的 Λ 值（20.1±2.0 和 18.4±1.9），表明两种酶在γ-HCH 转化过程中具有相似的反应机制。这是关于α-和γ-HCH 酶促脱氯化氢的 3D 同位素分馏的第一个数据集，更精确地描述了键的断裂，突出了多元素化合物特异性稳定同位素分析在表征不同转化过程（例如脱氯化氢和还原脱卤）方面的潜力。
