Spectroscopic studies of light-driven electron transfer

长距离电子传递在许多生物功能中起着重要的作用 酵素。在这些反应中，可能会发生自由基传输，并可能涉及到一种 单电子(ET)或质子耦合的电子转移反应(PET)。这个机制是通过 这些反应是由哪种蛋白质环境控制的才刚刚开始被阐明。宠物 核糖核苷酸还原酶(RNR)和光系统II(PSII)的反应是目前关注的焦点 此应用程序的。PSII进行光诱导的水的氧化和还原 胞质苯二酚。在PSII中，氧化还原活性酪氨酸YZ在 含锰放氧中心(GEC)和主要的电子给体。一个 第二个氧化还原活性酪氨酸Yo被初级电子供体氧化，但不是必需的 用于放氧活动。RnR催化核糖核苷酸还原为 脱氧核苷酸。在大肠杆菌RNR中，氧化还原活性酪氨酸Y122被认为是一个自由基 发起人。在这项建议中，将使用光谱方法，这将识别自由基 并阐明了这两种蛋白质的催化机理。研究也将是 进行了多肽模型，将用于测试研究产生的假设 自然系统的一部分。这项提议有三个具体目标。在A中，我们将使用瞬时EPR 和红外光谱来验证质子偶合机制的假说 电子转移区分了PSII中具有氧化还原活性的酪氨酸YO和YZ。因为这两个 PSII酪氨酸具有不同的氧化还原和动力学性质，将获得新的信息 关于生物PET反应的功能控制。在B中，我们将雇用一名新的 停流傅里叶变换红外光谱方法研究质子耦合电子的机理 调入RNR。我们将检验这个假设，即122年的氧化还原变化与 相邻多肽键的结构变化。在C语言中，我们将使用设计的测试版发夹模型 为了验证从酪氨酸到pi-pi发生质子耦合电子转移的假设 堆积的组氨酸。这一具体目标将有助于阐明主要、次要和 结构上定义的、易于处理的模型系统中的第三级相互作用。

Long distance electron transfer plays an important role in biological function in many enzymes. In these reactions, radical transport may occur and may involve transfer of an electron alone (ET) or a proton coupled, electron transfer reaction (PET). The mechanism by which the protein environment controls these reactions is just beginning to be elucidated. PET reactions in ribonucleotide reductase (RNR) and photosystem II (PSII) are the immediate focus of this application. PSII carries out the light-induced oxidation of water and reduction of plastoquinone. In PSII, a redox-active tyrosine, YZ, conducts electrons between the manganese-containing oxygen-evolving center (GEC) and the primary electron donor. A second redox-active tyrosine, YO, is oxidized by the primary electron donor, but is not required for oxygen-evolving activity. RNR catalyzes the reduction of ribonucleotides to deoxynucleotides. In E. coli RNR, a redox-active tyrosine, Y122, is proposed to be a radical initiator. In this proposal, spectroscopic methods will be employed, which will identify radical intermediates and elucidate catalytic mechanism in these two proteins. Studies will also be conducted of peptide maquettes, which will be used to test hypotheses generated from studies of the natural systems. This proposal has three specific aims. In A, we will use transient EPR and infrared spectroscopies to test the hypothesis that the mechanism of proton-coupled electron transfer distinguishes the redox-active tyrosines, YO and YZ, in PSII. Because the two PSII tyrosines have different redox and kinetic properties, new information will be acquired concerning the functional control of biological PET reactions. In B, we will employ a new method, stopped flow FT-IR spectroscopy, to probe the mechanism of proton-coupled electron transfer in RNR. We will test the hypothesis that redox changes at Y122 are coupled with structural changes in adjacent peptide bonds. In C, we will use designed beta hairpin maquettes to test the hypotheses that proton-coupled electron transfer can occur from tyrosine to a pi-pi stacked histidine. This specific aim will serve to elucidate the role of primary, secondary, and tertiary interactions in a structurally defined, tractable model system.