The Role of Xanthophylls in the Mechanism of Nonradiative Energy Dissipation in Photosynthesis

Harry A. Frank 9816759光合作用生物体含有保护机制，通过该机制，过量的光能在导致光合机构的光破坏之前被耗散掉。此外，从捕光色素-蛋白质复合物到光合反应中心的能量流受到高度调节。控制这些过程的分子特征还不清楚。叶黄素色素与这些机制有关，但其参与的确切性质尚不清楚。在这个项目中，将研究几种不同的叶黄素。要进行的实验包括稳态和时间分辨吸收和荧光光谱和电化学测定。光谱实验将测量叶黄素和叶绿素之间能量转移的效率和动力学。电化学实验将揭示分子在溶液中和结合在色素-蛋白质复合物中的氧化电位。本研究的主要目的是检查被认为在非辐射能量耗散中重要的每个分子因子，以揭示其在体内发生的详细分子机制。要探讨的因素包括叶黄素组成，聚集状态，pH值，磷酸化，能级的位置，和色素的氧化电位。的参与的叶黄素作为叶绿素荧光的直接或间接猝灭剂的问题将被检查。叶黄素通过能量转移或电子转移机制猝灭叶绿素荧光的假设将被检验。这些实验对于扩大我们的视野，了解光合生物如何保护自己免受过多的光能吸收，并对变化的环境条件作出反应，同时保持生存所必需的有效能量流是很重要的。叶黄素是任何观察过新英格兰秋叶明亮的橙子和黄色的人所熟悉的。然而，大多数观察者并不知道，这些引人注目的光合色素不仅仅为我们的生活提供了美感。它们是生物保护系统中的关键成分，可防止叶绿素（最重要的植物色素）在强光胁迫下分解。以一种尚未完全理解的方式，叶黄素能够在所谓的“叶黄素循环”中从一种形式转化为另一种形式并再次转化。“这个循环的分子成分似乎能够在催化叶绿素的破坏之前无害地使过量的激发态能量失活。有趣的是，相同的成分也可以调节光合蛋白之间吸收的太阳能的流动。本研究将精确地调查保护和流量调节是如何完成的。从几个高等植物和藻类系统的蛋白质制剂将进行系统的研究。将使用生物化学、分子生物学和光谱学工具的组合。这项研究的总体目标是阐明叶黄素循环如何工作的分子细节。这项工作有望更好地了解植物如何将太阳能转化为化学能，并在明亮的太阳条件下承受压力。

Harry A. Frank9816759Photosynthetic organisms contain protective mechanisms by which excess light energy is dissipated before it leads to the photodestruction of the photosynthetic apparatus. Also, energy flow from the light-harvesting pigment-protein complexes to the photosynthetic reaction center is highly regulated. The molecular features that control these processes are not well understood. Xanthophyll pigments have been implicated in the mechanisms, but the precise nature of their involvement is unclear. In this project, several different xanthophylls will be studied. The experiments to be performed include steady state and time-resolved absorption and fluorescence spectroscopy and electrochemical determinations. The spectroscopic experiments will measure the efficiencies and dynamics of energy transfer between the xanthophylls and chlorophyll. The electrochemical experiments will reveal the oxidation potentials of the molecules in solution and bound in the pigment-protein complexes. The major objective of this research to examine each of the molecular factors thought to be important in nonradiative energy dissipation in order to reveal the detailed molecular mechanism by which it takes place in vivo. The factors to be explored include xanthophyll composition, state of aggregation, pH, phosphorylation, position of the energy levels, and the oxidation potentials of the pigments. The question of the involvement of the xanthophylls as direct or indirect quenchers of chlorophyll fluorescence will be examined. The hypotheses that xanthophylls quench chlorophyll fluorescence by energy transfer or electron transfer mechanisms will be tested. The experiments are important in enlarging our view of how photosynthetic organisms protect themselves from excessive light energy absorption and respond to varying environmental conditions while maintaining efficient energy flow essential for survival.Xanthophylls are familiar to anyone who has observed the bright orange and yellow colors of Autumn leaves in New England. However, unbeknownst to most observers, these eye-catching photosynthetic pigments do more than provide aesthetic beauty to our lives. They are critical components in a biological protection system that prevents chlorophyll, the most essential plant pigment, from breaking down under high light stress. In a way that is not yet fully understood, xanthophylls are able to be converted from one form into another and back again in the so-called "Xanthophyll cycle." The molecular components of this cycle appear to be capable of harmlessly deactivating excess excited state energy before it catalyzes the destruction of chlorophyll. Interestingly, the same components may also regulate the flow of absorbed solar energy between photosynthetic proteins. This research will investigate precisely how the protection and flow regulation are accomplished. Protein preparations from several higher plant and algal systems will be systematically investigated. A combination of biochemical, molecular biological, and spectroscopic tools will be used. The overall goal of the research is to elucidate the molecular details of how the Xanthophyll cycle works. A better understanding of how plants convert solar energy into chemical energy and withstand stress under bright solar conditions is expected to be obtained from this work.