Materials Approaches for Understanding Biological Energy Transduction and Bifurcation

项目摘要/摘要 金属酶协调复杂的多质子/多电子反应，对人类生命至关重要，例如 固氮酶6H+/6E-还原氮气为氨，4H+/4E-还原氧气为水 单加氧酶。为了以最小的部分还原物种损失(PR)完成这些反应， 许多金属酶的氧化还原活性辅因子都位于活性部位附近。这些辅因 通常在底物结合之前负载几个电子和质子当量，从而能够选择性地 将基材转化为具有最小PRS损耗的产品。通常，PRS是高度反应性的，并导致细胞 损坏。对于细胞色素P450(CYP)和细胞色素C氧化酶(CcO)等酶，PrS的丢失，如 作为过氧化氢，与唐氏综合症、多发性硬化症和癌症等多种疾病有关。因此， 理解局域电子储备库对多质子/多电子选择性的影响 转化可能有助于上述疾病的治疗。 为了从根本上了解局部电子储库对选择性的影响 在多电子/多质子转化中，我们建议研究O2还原的活性和选择性 使用共价连接在导电电极上的铁卟啉作为氧气还原酶的人工模型。 我们将不使用分子电子储存库，而是将金属卟啉共价连接到碳和金属上。 氧化物电极表面。我们假设金属酶利用这些承载氧化还原的辅因子来提供 具有高度耦合的电子源的活性位置，并且它改变为 施主(电极)和受体(金属卟啉)将影响分叉步骤的动力学，从而导致 所需产品(H2O)或不需要的丙二醛(双氧水)。通过使用电极作为可调的代理， 氧化还原辅助因子，这些界面结构将允许多维控制距离、耦合和 电极与铁卟啉活性中心之间的电子转移驱动力，为基础研究提供了可能 在CcO和CYP等酶中导致PrS分叉和丢失的步骤。这些研究将 深入了解氧化还原活性辅因子如何影响金属酶中的产物分叉，这可能导致 涉及治疗或预防由生物系统中的过氧化氢损失引起的疾病的新方法。

PROJECT SUMMARY/ABSTRACT Metalloenzymes orchestrate complex multiproton/multielectron reactions critical to human life, such as the 6H+/6e- reduction of dinitrogen to ammonia by nitrogenase and the 4H+/4e- reduction of dioxygen to water by monooxygenase enzymes. To accomplish these reactions with minimal loss of partially reduced species (PRS), many metalloenzymes have redox-active cofactors located in close proximity to the active site. These cofactors are often loaded with several electron and proton equivalents prior to substrate binding, enabling selective conversion of the substrate to product with minimal PRS loss. Often, PRSs are highly reactive and lead to cellular damage. For enzymes such as Cytochrome P450 (CYP) and Cytochrome c Oxidase (CcO), loss of PRSs, such as H2O2, is linked to various diseases such as down syndrome, multiple sclerosis and cancer. Therefore, understanding the influence that local electron reservoirs have on the selectivity of multiproton/multielectron transformations may aid the treatment of the aforementioned diseases. In order to fundamentally understand the influence that local electron reservoirs have on the selectivity of multielectron/multiproton transformations, we propose to study the activity and selectivity for O2 reduction using iron porphyrins covalently attached to conductive electrodes as artificial models of O2 reducing enzymes. Rather than using a molecular electron reservoir, we will covalently attach metalloporphyrins to carbon and metal oxide electrode surfaces. We hypothesize that metalloenzymes utilize these redox-loaded cofactors to provide the active site with a highly coupled source of electrons, and that changes to the electron coupling between the donor (electrode) and acceptor (metalloporphyrin) will influence the kinetics of the bifurcating steps leading to the desired product (H2O) or the undesired PRS (H2O2). By using an electrode as a tunable surrogate for a redox cofactor, these interfacial constructs will allow a multidimensional control of the distance, coupling and electron transfer driving force between the electrode and iron porphyrin active site, enabling a fundamental study of the steps that lead to bifurcation and loss of PRS in enzymes such as CcO and CYP. These studies will provide insights into how redox-active cofactors influence product bifurcation in metalloenzymes, which may lead to new methods of treatment or prevention of diseases induced by H2O2 loss in biological systems.