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首页> 外文期刊>Catalysis science & technology >Insights into the dioxygen activation and catalytic mechanism of the nickel-containing quercetinase
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Insights into the dioxygen activation and catalytic mechanism of the nickel-containing quercetinase

机译：双氧激活和见解nickel-containing的催化机理quercetinase

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摘要

Quercetin 2,4-dioxygenase from Streptomyces sp. strain FLA (QueD(FLA)) is an enzyme of the monocupin family, which catalyzes the oxidative ring-cleaving reaction of quercetin using a nickel ion as the active site cofactor, and the iron ion that is necessary for most dioxygenases only shows low reactivity. To understand the reaction mechanism and the activation of dioxygen by the nickel ion, we performed QM/MM calculations to elucidate the reaction details and the special activation mechanism of this unique enzyme. Our calculations reveal two binding modes of dioxygen to the nickel ion, which can convert each other. Due to the overlap between the vacant d orbitals of nickel and the lone pair p orbitals of dioxygen and quercetin, electron transfer occurs from quercetin to dioxygen via the nickel center, thus, both dioxygen and quercetin can be activated by their binding to the nickel ion. On the basis of our calculations, the triplet reactant complex favors the catalytic reaction, and the whole reaction contains four elementary steps. In particular, a nonchemical process, the Op-Od bond rotation along the nickel center, is suggested to be rate-limiting with a free energy barrier of 19.9 kcal mol(-1). NBO analysis reveals that it is the change of the coordination of Op with the nickel ion that leads to the high energy barrier of this process. In general, owing to the activation of the substrate and dioxygen by the nickel ion, the formation and collapse of the five-membered ring intermediate are quite easy, and the cleavage of O-O is in concert with the breaking of two C-C bonds. Furthermore, when the metal cofactor is replaced by an iron ion, the rate-limiting step switches from the Op-Od bond rotation to the collapse of the five-membered ring intermediate, corresponding to a free energy barrier of 30.3 kcal mol(-1). This study sheds insight into the reaction mechanism of QueD and contributes to our general understanding of other nickel-containing enzymes.
机译：槲皮素2,从链霉菌属4-dioxygenase sp。应变佛罗里达州(qu(佛罗里达州))是一种酶monocupin家族催化氧化使用一个ring-cleaving槲皮素的反应镍离子的活性部位代数余子式,铁离子对大多数加双氧酶是必要的只显示低反应性。反应机理和分子氧的活化我们执行的镍离子,QM / MM计算阐明反应细节和特殊的激活机制独特的酶。绑定模式分子氧的镍离子,可以互相转换。镍和空d轨道之间的孤对p轨道的分子氧和槲皮素,电子转移发生从槲皮素双氧通过镍中心,因此,两种分子氧和槲皮素可以被激活的绑定到镍离子。三重态反应物计算复杂的支持催化反应,整个反应包含四个基本步骤。nonchemical过程,Op-Od债券旋转在镍中心,建议19.9病原的免费能量势垒千卡摩尔(1)。变化的协调与镍Op离子导致的能量势垒高的过程。衬底和镍离子,分子氧的五元环的形成与崩溃中间很容易,和乳沟oo是两个碳碳在音乐会的打破债券。取而代之的是一个铁离子,病原反应步骤开关从Op-Od键旋转崩溃的五元环中间体,对应于一个自由能量势垒为30.3千卡摩尔(1)。反应机理,并有助于我们的其他nickel-containing的一般理解酶。

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