Molecular Organization and Biodynamics of the Photosystem II Reaction Center

在光合作用初级过程中，有效的能量转化是由光化学反应中心在物理、化学和生物意义上的高度有序组织保证的。在光系统II （PSII）中，主要的电荷分离发生在由D1和D2蛋白和一些其他成分组成的色素蛋白复合体中，该复合体最近被分离出来并分析了化学和物理性质（Nanba和Satoh， 1987）。本研究从两个方面分析了PSII反应中心的组织结构。第一部分测定了分离反应中心的蛋白质亚基、色素和氧化还原辅因子的化学计量。EPR光谱分析了主给体（P-680）的取向，推测其三重态定位于叶绿素上，其四吡啶平面与膜倾斜约30‰。第二部分，重点分析了PSII反应中心D1亚基光调控转换的一些方面，包括在分离叶绿体中光调控D1蛋白合成的机制，以及参与D1前体蛋白c端加工的酶的表征。对不同条件下叶绿体ATP水平和D1蛋白合成速率的测定表明，可溶性基质部分ATP水平控制着D1蛋白的合成。在合成后进行的加工过程中所涉及的酶被提取和纯化。

The efficient energy transformation in the primary process of photosynthesis is ensured by the highly ordered organization of photochemical reaction centers, in physical, chemical and biological sense. In photosystem II (PSII), the primary charge separation takes place in a pigmentprotein complex consisted of D1 and D2 proteins and some other components, which has recently been isolated and the chemical and physical properties have been analyzed (Nanba and Satoh, 1987). In the present study, the organization of PSII reaction center has been analyzed in two aspects. In the first part, stoichiometries of protein subunits and of pigments and redox cofactors of the isolated reaction center have been determined. The orientation of the primary donor (P-680) has been analyzed by EPR spectroscopy and it is deduced that the triplet state is localized on a chlorophyll, the tetrapyrrolic plane of which is tilted about 30ﾟ to the membrane. In the second part, the analysis has been focussed on some aspects of light-regulated turnover of D1 subunit of the PSII reaction center, which include the mechanism of light-regulated synthesis of D1 protein in isolated chloroplasts and the characterization of an enzyme involved in the C-terminal processing of D1 precursor protein. Determination of the levels of ATP in chloroplasts and the rate of synthesis of D1 protein under various conditions suggested that the level of ATP in soluble, stromal fraction controls the synthesis of D1 protein. The enzyme involved in the processing taking place after the synthesis has been extracted and purified.