Liao Rong-Zhen, Siegbahn Per E M
Key Laboratory for Large-Format Battery Materials and System , Ministry of Education , School of Chemistry and Chemical Engineering , Huazhong University of Science and Technology , Wuhan 430074 , China . Email:
Department of Organic Chemistry , Arrhenius Laboratory , Stockholm University , SE-10691 Stockholm , Sweden . Email:
Chem Sci. 2015 May 1;6(5):2754-2764. doi: 10.1039/c5sc00313j. Epub 2015 Mar 2.
Benzoyl-CoA epoxidase is a dinuclear iron enzyme that catalyzes the epoxidation reaction of the aromatic ring of benzoyl-CoA with chemo-, regio- and stereo-selectivity. It has been suggested that this enzyme may also catalyze the deoxygenation reaction of epoxide, suggesting a unique bifunctionality among the diiron enzymes. We report a density functional theory study of this enzyme aimed at elucidating its mechanism and the various selectivities. The epoxidation is suggested to start with the binding of the O molecule to the diferrous center to generate a diferric peroxide complex, followed by concerted O-O bond cleavage and epoxide formation. Two different pathways have been located, leading to (2,3)-epoxy and (2,3)-epoxy products, with barriers of 17.6 and 20.4 kcal mol, respectively. The barrier difference is 2.8 kcal mol, corresponding to a diastereomeric excess of about 99 : 1. Further isomerization from epoxide to phenol is found to have quite a high barrier, which cannot compete with the product release step. After product release into solution, fast epoxide-oxepin isomerization and racemization can take place easily, leading to a racemic mixture of (2,3) and (2,3) products. The deoxygenation of epoxide to regenerate benzoyl-CoA by a diferrous form of the enzyme proceeds a stepwise mechanism. The C2-O bond cleavage happens first, coupled with one electron transfer from one iron center to the substrate, to form a radical intermediate, which is followed by the second C3-O bond cleavage. The first step is rate-limiting with a barrier of only 10.8 kcal mol. Further experimental studies are encouraged to verify our results.
苯甲酰辅酶A环氧化酶是一种双核铁酶，它能催化苯甲酰辅酶A芳香环的环氧化反应，具有化学、区域和立体选择性。有人认为这种酶也可能催化环氧化物的脱氧反应，这表明在双核铁酶中它具有独特的双功能性。我们报道了对这种酶的密度泛函理论研究，旨在阐明其反应机制和各种选择性。环氧化反应被认为始于O分子与二价铁中心结合生成二价铁过氧化物复合物，随后O - O键协同断裂并形成环氧化物。我们找到了两条不同的途径，分别生成(2,3)-环氧产物和(2,3)-环氧产物，其势垒分别为17.6和20.4千卡/摩尔。势垒差异为2.8千卡/摩尔，对应非对映体过量约为99∶1。发现环氧化物进一步异构化为苯酚的势垒相当高，无法与产物释放步骤竞争。产物释放到溶液中后，环氧化物 - 氧杂环庚三烯的异构化和外消旋化很容易发生，导致(2,3)和(2,3)产物的外消旋混合物。酶的二价铁形式将环氧化物脱氧以再生苯甲酰辅酶A的过程遵循逐步机制。首先发生C2 - O键断裂，同时一个电子从一个铁中心转移到底物上，形成一个自由基中间体，随后发生第二个C3 - O键断裂。第一步是限速步骤，势垒仅为10.8千卡/摩尔。鼓励进一步的实验研究来验证我们的结果。
