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J. Bacteriol., 03 1996, 1742-1749, Vol 178, No. 6
MG Sturr, TA Krulwich and DB Hicks
Escherichia coli GK100, with deletions in the operons encoding its two
terminal oxidases, cytochrome bo and ctyochrome bd, was complemented for
growth on succinate by a recombinant plasmid (pMS100) containing a 3.4-kb
region of DNA from alkaliphilic Bacillus firmus OF4. The complementing DNA
was predicted to encode five proteins, but neither sequence analysis nor
complementation experiments with subclones provided insight into the basis
for the complementation. Cytochrome difference spectra of everted membrane
vesicles from the transformed strain had characteristics of a cytochrome bd
spectrum but with features different from those observed for alkaliphile
membranes. To determine the bacterial source and identity of the structural
genes for the cytochrome bd in the transformed mutant, the complex was
extracted and partially purified. On sodium dodecyl sulfate-polyacrylamide
gels, two polypeptides were resolved from the preparation, 43 (subunit I)
and 27 (subunit II) kDa. An internal peptide from subunit I was sequenced,
and it yielded the same primary sequence as is found in positions 496 to
510 of E. coli appC. Consistent with the microsequencing results pMS100
failed to complement a triple mutant of E. coli carrying a deletion in appB
as well as in the cyo and cyd loci. The deduced sequence of AppBC had been
predicted to be very similar to the sequence of CydAB (J. Dassa et al.,
Mol. Gen. Genet. 229:341-352, 1991) but this is the first demonstration
that the former is indeed a cytochrome bd terminal oxidase. The enzyme
catalyzed oxygen uptake coupled to quinol or
N,N,N',N'-tetramethyl-p-phenylenediamine oxidation, and the activity was
sensitive to cyanide. No cross-reactivity to subunit-specific polyclonal
antibodies directed against the two individual subunits of cyd-encoded
cytochrome bd was detected. Since this is the second cytochrome bd
discovered in E. coli, it is proposed that the two complexes be designated
cytochrome bd-I (cydAB-encoded enzyme) and cytochrome bd-II (appBC-encoded
enzyme). In addition, cbdAB is suggested as a more appropriate gene
designation for cytochrome bd than either appBC or cyxAB.
Copyright © 1996, American Society for Microbiology
Purification of a cytochrome bd terminal oxidase encoded by the Escherichia coli app locus from a delta cyo delta cyd strain complemented by genes from Bacillus firmus OF4
Department of Biochemistry, Mount Sinai School of Medicine, City University of New York, USA.
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