Characterization of Hexachlorocyclohexane Isomer Dehydrochlorination by LinA1 and LinA2 Using Multi-element...

Area of Science:

• Biogeochemistry
• Environmental Chemistry
• Enzymology

Background:

• Hexachlorocyclohexane (HCH) is a persistent environmental pollutant.
• Aerobic microbial transformation of HCH primarily occurs via dehydrochlorination, catalyzed by LinA enzymes.
• Understanding the precise reaction mechanisms is crucial for bioremediation strategies.

Purpose of the Study:

• To investigate the reaction mechanisms of α- and γ-HCH dehydrochlorination by LinA1 and LinA2 enzymes.
• To apply multi-element compound-specific stable isotope analysis for detailed mechanistic insights.
• To differentiate between transformation processes using isotopic fractionation.

Main Methods:

• Multi-element compound-specific stable isotope analysis (C, Cl, H) was employed.
• Enzymatic dehydrochlorination of α-HCH (enantiomers) and γ-HCH by LinA1 and LinA2 was studied.
• Isotopic fractionation factors (ε_E) and dual-isotope parameters (Λ) were determined.

Main Results:

• Distinct isotopic fractionation values were observed for (+)α-HCH and (-)α-HCH, indicating different reaction pathways.
• Dual-isotope fractionation patterns were similar for both α-HCH enantiomers, suggesting conserved mechanistic features.
• Similar isotopic fractionation was observed for γ-HCH transformation by LinA1 and LinA2, indicating a conserved mechanism.

Conclusions:

• Multi-element stable isotope analysis provides a powerful tool to elucidate complex enzymatic reaction mechanisms.
• The study offers the first 3D isotope fractionation data for α- and γ-HCH dehydrochlorination.
• This approach can differentiate between various microbial transformation processes, including dehydrochlorination and reductive dehalogenation.