Spectroscopic studies of light-driven electron transfer

长距离电子转移在许多生物功能中起着重要作用， 内切酶在这些反应中，可能发生自由基传输，并且可能涉及自由基的转移。 电子转移反应（ET）或质子耦合的电子转移反应（PET）。的机制 蛋白质环境控制这些反应的机制才刚刚开始阐明。宠物 核糖核苷酸还原酶（RNR）和光系统II（PSII）的反应是当前的焦点 这个应用程序。PSII进行光诱导的水的氧化和 质体醌在PSII中，具有氧化还原活性的酪氨酸YZ在PSII和PSII之间传导电子。 含锰析氧中心（GEC）和主要电子供体。一 第二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 氧气释放活动。RNR催化核糖核苷酸还原为 脱氧核苷酸在大肠大肠杆菌RNR，一个氧化还原活性酪氨酸，Y122，被认为是自由基 引发剂在这个提议中，将采用光谱方法，这将确定自由基 中间体，并阐明这两种蛋白质的催化机制。研究还将 进行肽模型，将用于测试研究产生的假设 自然系统。这项建议有三个具体目标。在A中，我们将使用瞬态EPR 和红外光谱来验证质子耦合机制的假设， 电子转移区分PSII中的氧化还原活性酪氨酸YO和YZ。因为两 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，我们将雇用一名新的 用停流红外光谱法探讨了质子耦合电子转移的机理 在RNR中转移。我们将检验以下假设：Y122处的氧化还原变化与 相邻肽键的结构变化。在C中，我们将使用设计的beta发夹模型 为了检验质子偶联电子转移可以从酪氨酸发生到π-π的假设， 堆叠组氨酸。这一具体目标将有助于阐明初级、次级和 在结构上定义的，易处理的模型系统中的三级相互作用。

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.