Infrared Spectroscopic Studies of the Photosynthetic Oxygen-Evolving Complex

98 - 08934 -巴里1。光合作用的氧气进化发生在植物、绿藻和蓝藻中。这一过程对维持地球上需氧异养生命至关重要。本研究利用红外光谱和差红外光谱技术对光系统II的结构和功能进行了新的研究。这种酶进行水的光驱动氧化以形成氧和质体醌的还原以形成质体醌。这个过程发生在含锰的催化位点，它可以积累从水中产生氧气所必需的四种氧化等价物。催化位点的顺序氧化形式称为锡态，其中n表示形成的氧化等价物的数量。Mn的结合位点、Mn簇在S态的结构以及水氧化的化学机制尚不清楚。外部亚基，称为锰稳定蛋白，通过一种尚不清楚的机制改变酶的催化性能。本研究的具体目的是：1 .通过使用振动光谱继续研究S1到S2的跃迁，验证Mn在S1到S2跃迁中氧化会干扰连接或靠近金属簇的羧酸盐和羧酸残基的振动谱的假设；2。利用振动光谱将研究扩展到其他S态跃迁，验证其他S态跃迁的红外光谱差异可以被记录的假设，并用于获得光合水氧化机制的新信息；ⅲ。通过红外和其他光谱研究Mn团簇的光组装，测试Mn团簇的光驱动组装中可以形成中间体的假设，并使用红外和其他光谱研究。该中间体的形成可以用来获得有关催化位点结构和功能的更多信息。本研究的重点是光合作用中氧的演化机制。在绿色植物、藻类、蓝绿藻或蓝藻中发现了进行光合作用的氧气进化的蛋白质或酶。这种生产氧气的光合作用是地球上人类生命的基础，因为这个过程产生必需的营养物质并维持地球大气中的氧气。光产生的能量用来驱动析氧的化学反应。除非有能量输入，否则这些反应是不可能发生的。虽然光诱导的析氧或“水分解”是一种普遍存在的、非常重要的生物现象，但在这一过程中在酶上发生的化学反应，人们知之甚少。本研究的重点是利用振动光谱学来获得有关这些化学反应的更多信息。振动光谱学是一种测量原子振动频率和振幅的技术。这些频率和振幅反映了分子的结构。利用振动光谱学对反应过程中的水分解酶进行跟踪，可以获得更多的化学机理信息。光谱通过使用同位素标记和蛋白质诱变来解释。这些实验有望提供有关这种普遍存在的重要生物过程的新信息。

98-08934Barry 1.Technical Photosynthetic oxygen evolution occurs in plants, green algae, and cyanobacteria. This process is essential for maintenance of aerobic, heterotrophic life on earth. In this study, the techniques of infrared and difference infrared spectroscopy are used to obtain new information about the structure and function of photosystem II. This enzyme carries out the light driven oxidation of water to form oxygen and reduction of plastoquinone to form plastoquinol. This process occurs at a Mn-containing catalytic site, which can accumulate the four oxidizing equivalents necessary to generate oxygen from water. The sequentially oxidized forms of the catalytic site are called the Sn states, where n refers to the number of oxidizing equivalents formed. The binding sites for Mn, the structures of the Mn cluster in the S states, and the chemical mechanism of water oxidation are not understood. An extrinsic subunit, called the Mn stabilizing protein, alters the catalytic properties of the enzyme by an as yet unknown mechanism. The specific aims of this study are: I. to continue studies of the S1 to S2 transition through the use of vibrational spectroscopy, testing the hypothesis that oxidation of Mn in the S1 to S2 transition perturbs the vibrational spectrum of carboxylate and carboxylic acid residues that are ligating to or close to the metal cluster; II. to expand studies to other S state transitions through the use of vibrational spectroscopy, testingthe hypothesis that the difference infrared spectra of other S state transitions can be recorded and used to obtain new information about the mechanism of photosynthetic water oxidation; and III. to study the photoassembly of the Mn cluster through the use of infrared and other spectroscopies, tesing the hypothesis that an intermediate in the light-driven assembly of the Mn cluster can be formed and studied using infrared and other spectroscopies. The formation of this intermediate can be used to obtain more information about the structure and function of the catalytic site.2. Non-technicalThis research is focused on the mechanism of oxygen evolution in photosynthesis. The protein or enzyme that carries out photosynthetic oxygen evolution is found in green plants, algae, and blue-green algae or cyanobacteria. This type of oxygen-producing photosynthesis is the basis of human life on earth, because the process produces essential nutrients and maintains oxygen in the earth's atmosphere. The energy derived from light is used to drive the chemical reactions of oxygen evolution. These reactions are not possible unless that energy input is supplied. Although light-induced oxygen evolution or "water-splitting" is a ubiquitous, very important biological phenomenon, the chemical reactions, which occur during this process on the enzyme, are poorly understood. The focus of this study is the use of vibrational spectroscopy to obtain more information about these chemical reactions. Vibrational spectroscopy is a technique in which the frequencies and amplitudes of atomic vibrations are measured. These frequencies and amplitudes reflect the structure of a molecule. By using vibrational spectroscopy to follow the water-splitting enzyme as the reactions are performed, more information about the chemical mechanism will be obtained. The spectra are interpreted through the use of isotopic labeling and protein mutagenesis. These experiments are expected to yield new information about this ubiquitous, important biological process.