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Hot Biological Catalysis: Isothermal Titration Calorimetry to Characterize Enzymatic Reactions
Published on: April 4, 2014
A chlorine isotope effect for enzyme-catalyzed chlorination
Christopher M Reddy1, Li Xu, Nicholas J Drenzek
1Department of Marine Chemistry and Geochemistry, Woods Hole Oceanographic Institution, Woods Hole, Massachusetts 02543, USA. creddy@whoi.edu
Journal of the American Chemical Society
|December 6, 2002
Summary
Enzymatic chlorination shows a significant kinetic isotope effect, distinguishing natural chlorinated organic compounds (COCs) from human-made ones based on chlorine isotope ratios.
Area of Science:
- Environmental Chemistry
- Biochemistry
- Isotope Geochemistry
Background:
- Chlorinated organic compounds (COCs) are prevalent in various environmental and biological samples.
- Their origins can be either natural or anthropogenic, posing challenges for source attribution.
- Chlorine isotope ratios are potential markers for differentiating these sources.
Purpose of the Study:
- To investigate the chlorine isotope effect in enzyme-catalyzed chlorination.
- To determine if this effect can differentiate between natural and anthropogenic COCs.
- To assess the kinetic isotope effect (KIE) for enzymatic versus non-enzymatic chlorination.
Main Methods:
- Enzymatic chlorination of aromatic substrates (1,3,5-trimethylbenzene and 3,5-dimethylphenol) using chloroperoxidase from Caldariomyces fumago.
- Measurement of chlorine isotope ratios (k35/k37) to calculate the kinetic isotope effect (KIE).
- Comparison with non-enzymatic chlorination using hypochlorite.
Main Results:
- A substantial kinetic isotope effect (KIE) was observed for enzyme-catalyzed chlorination.
- KIE values were 1.012 for 1,3,5-trimethylbenzene and 1.011 for 3,5-dimethylphenol.
- Non-enzymatic chlorination yielded a significantly smaller KIE, highlighting the enzyme's role.
Conclusions:
- Enzyme-catalyzed chlorination exhibits a significant kinetic isotope effect.
- This enzymatic pathway can produce natural COCs with distinct chlorine isotope signatures.
- Chlorine isotope ratios offer a promising method for distinguishing natural from anthropogenic COCs.
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