Separated Concerted Proton-Electron Transfer with Biomimetic Models of Peroxidase

过氧化物酶仿生模型的分离协同质子电子转移

• 批准号: 8005702
• 负责人: Alexander Ray Fox
• 金额: $ 4.56万
• 依托单位: UNIVERSITY OF WASHINGTON
• 依托单位国家: 美国
• 财政年份: 2010
• 资助国家: 美国
• 起止时间: 2010-07-16 至 2013-07-15
• 项目状态: 已结题
• 来源: https://reporter.nih.gov/project-details/8005702
• 关键词: Acidity; Biochemical Process; Biological Models; Biomimetics; Chemical Models; Chemicals; Complex; Cytochrome P450; Discrimination; Electron Transport; Electrons; Enzyme Activation; Enzymes; Experimental Models; Foundations; Free Energy; Heme; Heme Iron; Hydrogen; Hydrogen Peroxide; In Vitro; Investigation; Iron; Kinetics; Ligands; Modeling; Movement; Peroxidases; Photosynthesis; Porphyrins; Protons; Reaction; Site; System; Thermodynamics; Work; biological systems; catalase; chemical kinetics; complex biological systems; electron donor; functional group; insight; oxidation; programs; protonation; public health relevance

DESCRIPTION (provided by applicant): A very wide variety of biochemical processes involve movement of protons and electrons, called proton-coupled electron transfer (PCET). This is particularly evident in the actions of heme enzymes, including cytochromes P-450, peroxidases, catalases, and many other enzymes. Both substrate oxidation and O2 or H2O2 activation by these enzymes require precise control of the movement of protons and electrons. The complexity of a full biological system, even in vitro, makes it difficult to analyze the features important to PCET. This proposal presents an experimental program that will develop a detailed mechanistic understanding of PCET in biomimetic systems relevant to the high-valent ferryl oxo intermediates compound I and compound II of these enzymes. Of particular importance are mechanisms where the transfer of protons and electrons occurs in a single kinetic step, as concerted proton-electron transfer (CPET). The CPET mechanism can avoid high-energy intermediates that would be otherwise be generated upon separate proton transfer (PT) or electron transfer (ET). An important distinction being made in this proposal is the concept of separated concerted proton-electron transfer (sCPET), in which the proton and electron to originate from or terminate at separate sites. This contrasts with hydrogen atom transfer (HAT) reactions where both PT and ET proceed from one single species to another single species. Herein, we propose electrochemical, spectroscopic, and chemical kinetic investigations using well-defined high-valent iron-heme (porphyrin)-oxo model complexes and select non-heme iron oxo complexes. Key thermodynamic information to be derived includes the acidity (pKa) and the reduction potential (E) of ferryl oxo and related intermediates using different porphyrin and axial ligands. A comprehensive kinetic profile for protonation and reduction of the ferryl oxo functional group will be developed using proton and electron donors that span a range of strengths, and Eyring analyses will provide the free energy barriers for these transformations. This will enable discrimination between sCPET and isolated ET-PT or PT-ET mechanisms in the biomimetic systems studied, and will provide an experimental foundation for extending the concept of sCPET to complex biological systems that incorporate ferryl heme and non-heme iron oxo intermediates. PUBLIC HEALTH RELEVANCE: Iron-containing enzymes execute remarkable chemical transformations related to cellular energy storage and conversion, photosynthesis, and neutralizing harmful materials. The work proposed here will provide greater understanding of how these enzymes achieve these tasks by developing simplified experimental models of these chemical transformations. Studies of these chemical model systems will provide important new insights into the functions and functioning of the full biological systems.

描述（由申请人提供）：各种各样的生物化学过程涉及质子和电子的运动，称为质子耦合电子转移（PCET）。这在血红素酶的作用中尤其明显，包括细胞色素P-450、过氧化物酶、过氧化氢酶和许多其他酶。这些酶的底物氧化和O2或H2 O2活化都需要精确控制质子和电子的运动。一个完整的生物系统的复杂性，即使在体外，使得它很难分析PCET重要的功能。该提案提出了一个实验方案，将开发一个详细的机械理解PCET在仿生系统相关的高价铁氧中间体化合物I和化合物II的这些酶。特别重要的是其中质子和电子的转移发生在单个动力学步骤中的机制，如协同质子-电子转移（CPET）。CPET机制可以避免在单独的质子转移（PT）或电子转移（ET）时产生的高能中间体。在这个提议中，一个重要的区别是分离协同质子-电子转移（sCPET）的概念，其中质子和电子起源于或终止于不同的位点。这与氢原子转移（HAT）反应形成对比，在HAT反应中PT和ET都从一个单一物种进行到另一个单一物种。在这里，我们提出了电化学，光谱和化学动力学调查使用定义明确的高价铁血红素（卟啉）-氧代模型配合物和选择非血红素铁氧代配合物。关键的热力学信息包括酸度（pKa）和还原电位（E）的铁氧和相关中间体使用不同的卟啉和轴向配体。一个全面的动力学曲线的质子化和还原的铁氧官能团将开发使用质子和电子供体，跨越一系列的强度，和艾林分析将提供这些转换的自由能垒。这将使sCPET和孤立的ET-PT或PT-ET机制之间的仿生系统研究的歧视，并将提供一个实验基础，将sCPET的概念扩展到复杂的生物系统，将铁血红素和非血红素铁氧中间体。 公共卫生关系：含铁酶执行与细胞能量储存和转换、光合作用和中和有害物质相关的显著化学转化。本文提出的工作将通过开发这些化学转化的简化实验模型来更好地理解这些酶如何实现这些任务。对这些化学模型系统的研究将为整个生物系统的功能和运作提供重要的新见解。