Theoretical study of dioxygen binding process in iron(III) catechol dioxygenase: "oxygen activation" vs "substrate activation".
Theoretical study of dioxygen binding process in iron(III) catechol dioxygenase: "oxygen activation" vs "substrate activation".
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DOI：
10.1021/jp806507k
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发表时间：
2009-03
期刊：
影响因子：
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通讯作者：
N. Nakatani;Y. Nakao;Hirofumi Sato;S. Sakaki
中科院分区：
文献类型：
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作者：
N. Nakatani;Y. Nakao;Hirofumi Sato;S. Sakaki
采用CASSCF/CASPT2方法研究了内二醇儿茶酚双加氧酶中非血红素铁(III)中心的双氧结合过程，以纳入参与Fe-O(2)相互作用的多构型特征。在此过程中，提出了两种替代机制：一种称为“氧活化”，另一种称为“底物活化”。我们的 CASSCF/CASPT2 计算结果支持氧活化。 SA（状态平均）-CASSCF/CASPT2方法评估的势能曲线和电子结构表明，在O（2）结合过程中，电荷转移直接发生从儿茶酚部分到双氧部分，产生eta（1）-end-on型铁（III）-超氧配合物。这是双氧活化的关键步骤。有趣的是，铁中心在O(2)结合过程中始终保持高自旋d(5)特征，这表明铁(III)中心没有接收来自儿茶酚部分的电荷转移。然而，这并不意味着铁(III)中心对于双氧活化不是必需的。铁(III)中心在儿茶酚双加氧酶中发挥的重要作用是调节O(2)的能级以诱导电荷从儿茶酚酸部分转移到双氧部分。除了eta(1)-末端型铁(III)-超氧络合物外，还优化了eta(2)-侧型铁(III)-超氧络合物。该物质比 eta(1)-end-on 型铁(III)-超氧配合物更稳定，表明其在催化循环的早期阶段被认为是稳定的异构体。
Dioxygen binding process of nonheme iron(III) center in intradiol catechol dioxygenase was investigated with CASSCF/CASPT2 method to incorporate multiconfigurational character participating in Fe-O(2) interaction. In this process, two alternative mechanisms were proposed: one is called "oxygen activation" and the other is called "substrate activation". Our CASSCF/CASPT2-calculated results support the oxygen activation. Potential energy curves and electronic structure evaluated with SA(state-averaged)-CASSCF/CASPT2 method indicate that the charge transfer directly occurs from the catecholate moiety to the dioxygen moiety in the O(2) binding process, to produce eta(1)-end-on type iron(III)-superoxo complex. This is the key step of the dioxygen activation. Interestingly, the iron center always keeps high spin d(5) character during the O(2) binding process, indicating the iron(III) center does not receive charge transfer from the catecholate moiety. However, this does not mean that the iron(III) center is not necessary to the dioxygen activation. The important role which the iron(III) center plays in catechol dioxygenase is to adjust the energy level of O(2) to induce the charge transfer from the catecholate moiety to the dioxygen moiety. Besides the eta(1)-end-on iron(III)-superoxo complex, eta(2)-side-on type iron(III)-superoxo complex is also optimized. This species is more stable than the eta(1)-end-on type iron(III)-superoxo complex, suggesting that this is considered as a stable isomer in the early stage of the catalytic cycle.