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

二甲亚砜（DMSO）呼吸作用是已知的，以支持许多细菌的细胞生长在非有氧条件下。研究了DMSO呼吸作用的末端酶--DMSO reeducates。编码光合细菌Rhodobacter sphaeroides f.sp.denitirficans的DMSO还原酶的基因，其含有钼辅因子，使用寡核苷酸探针分离，所述寡核苷酸探针基于纯化的酶的内部氨基酸序列进行了测序。DMSO还原酶基因编码822个氨基酸（2466个碱基对，Mw 89，206），作为具有42个氨基酸的信号肽的前体形式。推导的氨基酸序列与大肠杆菌中含有钼辅因子的三甲基胺N-氧化物还原酶（48%）、生物素亚砜还原酶（44%）和DMSO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。它不仅同化DMSO，而且同化TMAO、蛋氨酸亚砜、生物素亚砜和其他合成烷基芳基亚砜。它在还原S-型和R-型方面具有极高的立体特异性，以光学纯的形式获得。该酶的立体选择性转化在有机合成中具有重要的应用价值，近年来研究表明，水生藻类二甲基硫（DMS）的全球排放与其还原硫化物的生物活性有关。为了更好地理解生物对环境的贡献，需要进一步阐明DMSO及其还原酶的存在以及DMS在水圈中的排放。

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.