A novel gene, torB, for trimethylamine N-oxide reductase in Escherichia coli.

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Abstract
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 MuI. The mutation was localized at 0.7 min 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.