The major inducible trimethylamine oxide reductase was purified from Salmonella typhimurium LT2. The molecular weights of the native enzyme were estimated to be 332,000 by gel filtration and 170,000 by nondenaturing disc gel electrophoresis. In sodium dodecyl sulfate-gel electrophoresis, the enzyme formed a single band of molecular weight 84,000. The isoelectric point was 4.28. Maximum activity was at pH 5.65 and 45 degrees C. Reduced flavin mononucleotide, but not reduced flavin adenine dinucleotide, served as an electron donor. The Km for trimethylamine oxide was 0.89 mM and Vmax was 1,450 U/mg of protein. The enzyme reduced chlorate with a Km of 2.2 mM and a Vmax of 350 U/mg of protein.

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