Spectroscopic studies of light-driven electron transfer

描述(申请人提供)：这项提案有三个具体目标，探索蛋白质中三组不同的生物相关电子转移反应。这些电子转移反应涉及氧化还原活性氨基酸残基和叶绿素(Chl)。 我们将检验三个假设：(A)酪氨酸自由基自旋密度以一种超敏感的、依赖于序列的方式离域到多肽/蛋白质酰胺键中；(13)电子转移连接的质子转移区分光系统II(PSID)中具有氧化还原活性的酪氨酸；以及(C)叶绿素互变异构化状态的差异导致PSII和光系统I(PSI)中初级Chl供体的中点电位的差异。 为了解决这些问题，将使用电子顺磁共振光谱、傅里叶变换红外光谱和瞬时动力学。在合作努力中，还将使用电子自旋回波包络调制和密度泛函理论。 蛋白质中的长距离电子转移涉及氧化还原活性基团对之间的逐步电子转移反应，这些基团充当催化中间体。这些假体基团包括共价和非共价结合的辅因子，如血红素、叶绿素和叶绿素，以及氨基酸侧链。这项研究项目的一个重要的长期目标是确定这些氧化还原中间体的结构和环境的变化如何影响电子转移速率。这个建议的总体目标是阐明结构和环境因素，这些因素在PSII和PSI的中点电位和电子转移的控制中非常重要。将在这里描述的光谱研究将提供关于光合作用反应中心中电子传递机制的新信息。影响电子转移反应效率的因素可能在其他酶催化的氧化还原反应中也很重要，而光合作用蛋白提供了一个独特而有用的模型系统，因为这些反应可以受光控制。

DESCRIPTION (provided by applicant): This proposal has three specific aims, which probe three different sets of biologically relevant electron transfer reactions in proteins. These electron transfer reactions involve redox-active amino acid residues and chlorophyll (chl). We will test three hypotheses: (A) that tyrosyl radical spin density delocalizes into the peptide/protein amide bond in a conformationaUy-sensitive, sequence-dependent manner; (13) that electron transfer-linked proton transfer distinguishes the redox-active tyrosines in photosystem II (PSID; and (C) that a difference in chlorophyll tautomerization state contributes to the difference in midpoint potential between the primary chl donors in PSII and photosystem I (PSI). To address these questions, electron paramagnetic resonance spectroscopy, Fourier-transform infrared spectroscopy, and transient kinetics will be used. In collaborative efforts, electron spin-echo envelope modulation and density functional theory will also be employed. Long distance electron transfer in proteins involves step-wise electron transfer reactions between pairs of redox-active prosthetic groups, which act as catalytic intermediates. These prosthetic groups include covalently and non-covalently bound cofactors, such as heme, pheophytin, and chl, as well as amino acid side chains. An important long-term goal of this research project is to determine how electron transfer rates are influenced by changes in the structure and environment of these redox intermediates. The overall goal of this proposal is to elucidate the structural and environmental factors that are important in the control of midpoint potential and electron transfer in PSII and PSI. The spectroscopic studies to be described here will give new information concerning electron transfer mechanisms in photosynthetic reaction centers. The factors that influence the efficiency of electron transfer reactions are likely to be important in other enzymatic redox reactions, and photosynthetic proteins provide a unique and useful model system, because the reactions can be controlled by light.