Measurement and Prediction of Chlorine Kinetic Isotope Effects in Enzymatic Systems

Szatkowski, Lukasz; Manna, Rabindra Nath; Grzybkowska, Anna; Kamiński, Rafał M.; Dybała-Defratyka, Agnieszka; Paneth, Piotr

doi:10.1016/bs.mie.2017.07.021

Cited by 9 publications

(8 citation statements)

References 97 publications

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“…The apparent differences in H isotope fractionation imply subtle differences in the mechanisms of dehydrochlorination. In fact, differences in 2 H-AKIEs in elimination reactions have been interpreted as differences in transition state structure where one distinguishes the timing of proton abstraction and leaving group departure. − Such interpretations have been applied in theoretical studies with LinA to assess concerted vs stepwise dehydrochlorination mechanisms for different HCH isomers (γ-HCH and β-HCH). ,, Evidence from our data indicates that such differences may also arise for the same HCH isomer when different LinA variants catalyze dehydrochlorination. Previous works suggested that the protonation state of the His73 residue is responsible for H abstraction from HCH and determines the extent of C–H bond cleavage in the transition state. , We hypothesize that this phenomenon could also have modulated the 2 H-AKIE of the dehydrochlorination by LinA1 and LinA2.…”

Section: Resultsmentioning

confidence: 90%

Kinetic Isotope Effects of the Enzymatic Transformation of γ-Hexachlorocyclohexane by the Lindane Dehydrochlorinase Variants LinA1 and LinA2

Schilling

Hess

Bolotin

et al. 2019

Environ. Sci. Technol.

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Compound-specific isotope analysis (CSIA) can provide insights into the natural attenuation processes of hexachlorocyclohexanes (HCHs), an important class of persistent organic pollutants. However, the interpretation of HCH stable isotope fractionation is conceptually challenging. HCHs exist as different conformers that can be converted into each other, and the enzymes responsible for their transformation discriminate among those HCH conformers. Here, we investigated the enzyme specificity of apparent 13C- and 2H-kinetic isotope effects (AKIEs) associated with the dehydrochlorination of γ-HCH (lindane) by two variants of the lindane dehydrochlorinases LinA1 and LinA2. While LinA1 and LinA2 attack γ-HCH at different trans-1,2-diaxial H–C–C–Cl moieties, the observed C and H isotope fractionation was large, typical for bimolecular eliminations, and was not affected by conformational mobility. 13C-AKIEs for transformation by LinA1 and LinA2 were the same (1.024 ± 0.001 and 1.025 ± 0.001, respectively), whereas 2H-AKIEs showed minor differences (2.4 ± 0.1 and 2.6 ± 0.1). Variations of isotope effects between LinA1 and LinA2 are small and in the range reported for different degrees of C–H bond cleavage in transition states of dehydrochlorination reactions. The large C and H isotope fractionation reported here for experiments with pure enzymes contrasts with previous observations from whole cell experiments and suggests that specific uptake processes by HCH-degrading microorganisms might modulate the observable HCH isotope fractionation at contaminated sites.

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Section: Resultsmentioning

confidence: 90%

Kinetic Isotope Effects of the Enzymatic Transformation of γ-Hexachlorocyclohexane by the Lindane Dehydrochlorinase Variants LinA1 and LinA2

Schilling

Hess

Bolotin

et al. 2019

Environ. Sci. Technol.

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“…The other tool is based on the theoretical KIEs prediction. The theoretical insight from some of us, based on full enzymatic model [15] allowed to characterize mechanistic pathways viable for the transformation of γ-HCH by LinA and eventually led to the carbon, chlorine, and hydrogen KIEs prediction [16,17]. Some discrepancies, such as much larger predicted hydrogen KIE, have been found in the data coming from these two approaches, thus opening room for debate.…”

Section: Introductionmentioning

confidence: 99%

Can Alkaline Hydrolysis of γ-HCH Serve as a Model Reaction to Study Its Aerobic Enzymatic Dehydrochlorination by LinA?

Kannath

Adamczyk

et al. 2019

IJMS

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Hexachlorocyclohexane (HCH) isomers constitute a group of persistent organic pollutants. Their mass production and treatment have led to a global environmental problem that continues to this day. The characterization of modes of degradation of HCH by isotope fractionation is a current challenge. Multi isotope fractionation analysis provides a concept to characterize the nature of enzymatic and chemical transformation reactions. The understanding of the kinetic isotope effects (KIE) on bond cleavage reaction contributes to analyses of the mechanism of chemical and enzymatic reactions. Herein, carbon, chlorine, and hydrogen kinetic isotope effects are measured and predicted for the dehydrochlorination reaction of γ-HCH promoted by the hydroxyl ion in aqueous solution. Quantum mechanical (QM) microsolvation with an implicit solvation model and path integral formalism in combination with free-energy perturbation and umbrella sampling (PI-FEP/UM) and quantum mechanical/molecular mechanical QM/MM potentials for including solvent effects as well as calculating isotope effects are used and analyzed with respect to their performance in reproducing measured values. Reaction characterization is discussed based on the magnitudes of obtained isotope effects. The comparative analysis between the chemical dehydrochlorination of γ-HCH in aqueous media and catalyzed reaction by dehydrochlorinase, LinA is presented and discussed. Based on the values of isotope effects, these two processes seem to occur via the same net mechanism.

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“…Chlorine isotopic fractionation is a very informative tool used in many life-controlling processes 21 , including environmental 22 – 25 , geochemical 26 – 30 and biochemical 31 – 33 studies. Therefore a detailed understanding of this phenomenon is an important scientific (but with practical consequences in the interpretation of experimental results 34 and analytical techniques 35 – 37 ) issue. It is thus not surprising that studies on model reactions 38 and theoretical predictions have been performed 33 , 34 , 39 – 41 .…”

Section: Introductionmentioning

confidence: 99%

Unprecedently large 37Cl/35Cl equilibrium isotopic fractionation on nano-confinement of chloride anion

Pokora

Paneth

2022

Sci Rep

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Confinement can result in unusual properties leading to new, exciting discoveries in the nano-realm. One such consequence of confinement at the nanoscale is extremally large isotopic fractionation, especially at sub-van der Waals distances. Herein, on the example of chlorine isotope effects, we show that at conditions of nanoencapsulation these effects may reach values by far larger than observed for the bulk environment, which in the case of nanotubes can lead to practical applications (e.g., in isotopic enrichment) and needs to be considered in analytical procedures that employ nanomaterials.

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Measurement and Prediction of Chlorine Kinetic Isotope Effects in Enzymatic Systems

Cited by 9 publications

References 97 publications

Kinetic Isotope Effects of the Enzymatic Transformation of γ-Hexachlorocyclohexane by the Lindane Dehydrochlorinase Variants LinA1 and LinA2

Kinetic Isotope Effects of the Enzymatic Transformation of γ-Hexachlorocyclohexane by the Lindane Dehydrochlorinase Variants LinA1 and LinA2

Can Alkaline Hydrolysis of γ-HCH Serve as a Model Reaction to Study Its Aerobic Enzymatic Dehydrochlorination by LinA?

Unprecedently large 37Cl/35Cl equilibrium isotopic fractionation on nano-confinement of chloride anion

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