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

众所周知，二甲基亚砜（DMSO）的呼吸作用支持许多细菌在无氧条件下的细胞生长。研究了DMSO呼吸作用的末端酶DMSO reeducates。利用寡核苷酸探针对光合细菌球形红杆菌（Rhodobacter sphaeroides f.sp.denitirficans）含有钼辅助因子的DMSO还原酶基因进行了分离，并根据酶的内部氨基酸序列合成了寡核苷酸探针。DMSO还原酶基因编码822个氨基酸（2466个碱基对，分子量89,206）作为具有42个氨基酸的信号肽的前体形式。推导出的氨基酸序列与大肠杆菌中含有钼辅助因子的三甲基胺n -氧化物还原酶（48%）、生物素亚砜还原酶（44%）和二甲基亚砜还原酶（29%）具有较高的同源性。DMSO还原酶具有广泛的底物特异性。它不仅能吸收二甲基亚砜，还能吸收氧化三甲胺、蛋氨酸亚砜、生物素亚砜等合成烷基芳基亚砜。它具有极高的立体专一性还原s型和r型的光纯形式。该酶的立体选择性转化在有机合成中有很大的应用。水生环境中二甲基硫化物（DMS）的全球排放最近被发现与硫化合物还原的生物活性有关。为了进一步了解DMSO及其还原酶在水圈中的存在和DMS的排放，需要进一步明确其对环境的生物学贡献。

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.