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J. Bacteriol., 10 1996, 5699-5705, Vol 178, No. 19
B Lei and SC Tu
The oxidation of dibenzothiophene to dibenzothiophene sulfone has been
linked to the enzyme encoded by the sox/dszC gene from Rhodococcus sp.
strain IGTS8 (S. A. Denome, C. Oldfield, L. J. Nash, and K. D. Young, J.
Bacteriol. 176:6707-6717, 1994; C. S. Piddington, B. R. Kovacevich, and J.
Rambosek, Appl. Environ. Microbiol. 61:468-475, 1995). However, this enzyme
has not been characterized, and the type of its catalytic activity remains
unclassified. In this work, the sox/dszC gene was overexpressed in
Escherichia coli, a procedure for the purification of the expressed enzyme
was developed, and the properties of and the reactions catalyzed by the
purified enzyme were characterized. This enzyme binds one flavin
mononucleotide (Kd, 7 micrometers) or reduced flavin mononucleotide (FMNH2)
(Kd < 10(-8) M) per 90,200-Da homodimer, and FMNH2 is an essential
cosubstrate for its activity. Patterns of product formation were examined
under different FMNH2 availabilities, and results indicate that this enzyme
catalyzes a stepwise conversion of dibenzothiophene to the corresponding
sulfoxide and subsequently to the sulfone. On the basis of isotope labeling
patterns with H2(18)O and 18O2, dibenzothiophene sulfoxide and sulfone
obtained their oxygen atom(s) from molecular oxygen rather than water in
their formation from dibenzothiophene. The enzyme also utilizes benzyl
sulfide and benzyl sulfoxide as substrates. Hence, it is identified as a
sulfide/sulfoxide monooxygenase. This monooxygenase is similar to the
microsomal flavin- containing monooxygenase but is unique among microbial
flavomonooxygenases in its ability to catalyze two consecutive
monooxygenation reactions.
Copyright © 1996, American Society for Microbiology
Gene overexpression, purification, and identification of a desulfurization enzyme from Rhodococcus sp. strain IGTS8 as a sulfide/sulfoxide monooxygenase
Department of Biochemical and Biophysical Sciences, University of Houston, Texas 77204-5934, USA.
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