Materials Approaches for Understanding Biological Energy Transduction and Bifurcation

项目总结/摘要 金属酶协调对人类生命至关重要的复杂多质子/多电子反应，例如 固氮酶将二氮还原为氨的6 H +/6 e-还原和固氮酶将二氧还原为水的4 H +/4 e-还原。 单加氧酶为了以部分还原物质（PRS）的最小损失完成这些反应， 许多金属酶具有位于活性位点附近的氧化还原活性辅因子。这些辅助因子 通常在底物结合之前装载有几个电子和质子等价物， 以最小的PRS损失将底物转化为产物。通常，PRS是高度反应性的，并导致细胞凋亡。 损害对于酶如细胞色素P450（CYP 450）和细胞色素c氧化酶（CcO）， 如H2 O2，与各种疾病如唐氏综合症，多发性硬化症和癌症有关。因此，我们认为， 了解局部电子库对多质子/多电子选择性的影响 这些转化可能有助于治疗上述疾病。 为了从根本上理解局域电子库对选择性的影响， 的多电子/多质子转换，我们建议研究的活性和选择性O2还原 使用共价连接到导电电极上的铁卟啉作为O 2还原酶的人工模型。 我们将金属卟啉共价连接到碳和金属上，而不是使用分子电子库 氧化物电极表面。我们假设金属酶利用这些负载氧化还原的辅因子来提供 活性位点具有高度耦合的电子源，并且改变为 供体（电极）和受体（金属卟啉）将影响分叉步骤的动力学， 所需产物（H2O）或不需要的PRS（H2 O2）。通过使用电极作为可调替代物， 氧化还原辅因子，这些界面构建体将允许多维控制距离、偶联和 电极和铁卟啉活性位点之间的电子转移驱动力，使得能够进行基础研究 的步骤，导致分支和损失的PRS酶，如CcO和酶。这些研究将 提供见解如何氧化还原活性辅因子影响产品的分歧，在金属酶，这可能导致 涉及治疗或预防由生物系统中的H2 O2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.