类球红杆菌羰基还原酶不对称催化还原性能与底物结构的关系

Relationship between Catalytic Asymmetric Reduction Ability of Carbonyl Reductase of Rhodobacter sphaeroides and Substrate Structure

将类球红杆菌(Rhodobacter sphaeroides)全细胞及其分离得到的羰基还原酶用于不对称催化还原多种潜手性酮类化合物,通过比较产物的收率、ee值、酶活力以及酶学动力学常数Km,探讨了类球红杆菌的催化还原性质与底物结构的关系.结果表明,对于类球红杆菌全细胞不对称催化还原苯乙酮衍生物,产物ee值的变化遵循Prelg规则,产物收率与底物苯环及侧链上取代基团的性质有关;对于脂肪酮催化还原,产物收率随底物链长的增加和分子量的增大而降低,随支链数目的增加而升高,产物ee值的变化也遵循Prelg规则.利用羰基还原酶不对称催化还原潜手性酮类化合物发现,对于芳香酮类化合物,酶对α位为强电负性基团的底物专一性较强;对于脂肪酮类化合物,酶对五碳脂肪酮的专一性较高.利用酶直接催化还原反应产物的ee值均为99%左右,表明酶较全细胞有更高的立体选择性.

The asymmetric reduction of ketones catalyzed by whole cells or carbonyl reductase ofRhodobacter sphaeroides was studied. The relationship between catalytic ability of Rhodobacter sphaeroides and the structure of substrates was determined by evaluating the yields, ee value, enzyme activity, and kinetic constant （Kin value） of enzyme. The ee value followed the Prelg rule. The yield was related to the substitution on the benzene ring and side-chain of acetophenone derivatives. The yield decreased with increasing length of the chain and molecular mass of the substrates but was enhanced with the increase of the number of branched-chains for aliphatic ketones. The results of asymmetric reduction of latent chiral ketones by carbonyl reduetase showed that the enzyme had a high specificity for pentanone in aliphatic ketones and for the acetophenone derivates that contained a withdrawing group at a-position. In the enzyme-catalyzed asymmetric hydrogenation, all the product ee values were around 99%, indicating that the carbonyl reductase had higher stereoselectivity than the whole cells.