Trimethylamine
N-oxide (TMAO) reductase which is involved in anaerobic respiration is one of the molybdenum-containing enzymes in
Escherichia coli. A mutant defective in the activity of TMAO reductase was isolated by inserting phage Mu
dI. The mutation was localized at 0.7min adjacent to
chlG on the
E. coli chromosome, and was designated
torB. The
torB mutant grown anaerobically with TMAO contained 10-30% of the enzyme activity in the parent strain grown under the same condition and about 80% of the enzyme protein immuno-reactive with an antiserum against the TMAO reductase. The content of molybdopterin, an organic moiety of molybdenum cofactor, in the immuno-precipitate from extracts of the
torB mutant was rather low, about 60% of that in the immuno-precipitate from the parent strain. The mutant showed a normal level of another
molybdenum enzyme nitrate reductase activity when anaerobically grown with nitrate. These findings suggest that the
torB gene is involved in the formation of the active enzyme of TMAO reductase through the processing of molybdenum cofactor. There was a marked expression of
torB under anaerobic conditions, and TMAO was not required for it.
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