Trichloroethylene oxidation by toluene dioxygenase

Area of Science:

• Biochemistry
• Environmental Microbiology
• Enzyme Catalysis

Background:

• Trichloroethylene (TCE) is a widespread environmental pollutant.
• Understanding the biodegradation pathways of TCE is crucial for remediation strategies.
• Toluene dioxygenase (TDO) is a key enzyme in aromatic hydrocarbon metabolism.

Purpose of the Study:

• To elucidate the oxidation mechanism of trichloroethylene (TCE) by toluene dioxygenase (TDO).
• To identify the oxidation products and intermediates of TCE metabolism by TDO.
• To compare the TCE oxidation pathway by TDO with those of other known oxygenases.

Main Methods:

• Purification of toluene dioxygenase from recombinant E. coli strains.
• Incubation of TCE with purified TDO and analysis of oxidation products using various analytical techniques.
• Use of isotopically labeled TCE ([14C]TCE and deuterated TCE) and D2O to trace metabolic pathways.

Main Results:

• TDO oxidized TCE primarily to formic acid and glyoxylic acid.
• No evidence of dichloroacetic acid, chloral, phosgene, carbon monoxide, or carbon dioxide as products.
• [14C]TCE was covalently attached to protein and NADPH, indicating reactive intermediates.
• Deuterium labeling confirmed that both carbon atoms of TCE contribute to formic acid formation.
• The data suggest an oxygenation mechanism not involving epoxide, dioxetane, or dihydroxy intermediates.

Conclusions:

• Toluene dioxygenase catalyzes a unique oxidation of trichloroethylene.
• The mechanism differs significantly from those proposed for cytochrome P-450 and methane monooxygenase.
• The findings provide insights into the enzymatic detoxification of chlorinated solvents.