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J. Bacteriol., Jan 1997, 90-96, Vol 179, No. 1
LM Newman and LP Wackett
Trichloroethylene is oxidized by several types of nonspecific bacterial
oxygenases. Toluene 2-monooxygenase from Burkholderia cepacia G4 is
implicated in trichloroethylene oxidation and is uniquely suggested to be
resistant to turnover-dependent inactivation in vivo. In this work, the
oxidation of trichloroethylene was studied with purified toluene 2-
monooxygenase. All three purified toluene 2-monooxygenase protein
components and NADH were required to reconstitute full trichloroethylene
oxidation activity in vitro. The apparent Km and Vmax were 12 microM and 37
nmol per min per mg of hydroxylase component, respectively. Ten percent of
the full activity was obtained when the small-molecular-weight enzyme
component was omitted. The stable oxidation products, accounting for 84% of
the trichloroethylene oxidized, were carbon monoxide, formic acid,
glyoxylic acid, and covalently modified oxygenase proteins that constituted
12% of the reacted [14C]trichloroethylene. The stable oxidation products
may all derive from the unstable intermediate trichloroethylene epoxide
that was trapped by reaction with 4-(p-nitrobenzyl)pyridine. Chloral
hydrate and dichloroacetic acid were not detected. This finding differs
from that with soluble methane monooxygenase and cytochrome P-450
monooxygenase, which produce chloral hydrate. Trichloroethylene- dependent
inactivation of toluene 2-monooxygenase activity was observed. All of the
protein components were covalently modified during the oxidation of
trichloroethylene. The addition of cysteine to reaction mixtures partially
protected the enzyme system against inactivation, most notably protecting
the NADH-oxidoreductase component. This suggested the participation of
diffusible intermediates in the inactivation of the oxidoreductase.
Copyright © 1997, American Society for Microbiology
Trichloroethylene oxidation by purified toluene 2-monooxygenase: products, kinetics, and turnover-dependent inactivation
Department of Biochemistry, the Biological Process Technology Institute, University of Minnesota, St. Paul 55108, USA.
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