Structure and Function of Mo-enzyme and its Role in Global S-Cycling

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Dimethyl sulfoxide (DMSO) respiration is known to support the cell growth of many bacteria under unaerobic conditions. The terminal enzyme of the DMSO respiration, DMSO reeducates, was studied. The gene enconding DMSO reductase, which contains a molybdenum cofactor, of the photosynthetic bacterium Rhodobacter sphaeroides f.sp.denitirficans was isolated using an oligonucleotide probe, which was synthsized based on an internal amino acid sequence of the purified enzyme. The DMSO reductase gene coded 822 amino acids (2466 base pairs, Mw 89,206) as a precursor form having a signal peptide of 42 amino acids. The deduced amino acid sequence had high homology with those of some enzymes containing a molybdenum cofactor : trimethyl amine N-oxide reductase (48%), biotin sulfoxide reductase (44%), and DMSO reductase (29%) of Escherichia coli.DMSO reductase has a broad substrate specificity. It assimilates not only DMSO but also TMAO,methionine sulfoxide, biotin sulfoxide and other synthetic alkyl aryl sulfoxides. It has extremely high stereospecificity in reduction of S-form and R-form was obtained in a optically-pure form. Stereo-selective conversion by this enzyme was of great use for organic synthesis.Global emission of dimethyl sulfide (DMS) from aquatic environmentis recentlyrevealed to be related with biological activity of reduction of sulfur compounds. Presence of DMSO and its reducing enzymes and emission of DMS in hydrosphere should be clarified further to understand the biological contribution to environment.