Abstract：
In oxygenic photosynthetic systems, the cytochrome b6f (Cytb6f) complex (plastoquinol:plastocyanin oxidoreductase) is a heart of the hub that provides connectivity between photosystems (PS) II and I. In this review, the structure and function of the Cytb6f complex are briefly outlined, being focused on the mechanisms of a bifurcated (two-electron) oxidation of plastoquinol (PQH2). In plant chloroplasts, under a wide range of experimental conditions (pH and temperature), a diffusion of PQH2 from PSII to the Cytb6f does not limit the intersystem electron transport. The overall rate of PQH2 turnover is determined mainly by the first step of the bifurcated oxidation of PQH2 at the catalytic site Qo, i.e., the reaction of electron transfer from PQH2 to the Fe2S2 cluster of the high-potential Rieske iron-sulfur protein (ISP). This point has been supported by the quantum chemical analysis of PQH2 oxidation within the framework of a model system including the Fe2S2 cluster of the ISP and surrounding amino acids, the low-potential heme b6L, Glu78 and 2,3,5-trimethylbenzoquinol (the tail-less analog of PQH2). Other structure-function relationships and mechanisms of electron transport regulation of oxygenic photosynthesis associated with the Cytb6f complex are briefly outlined: pH-dependent control of the intersystem electron transport and the regulatory balance between the operation of linear and cyclic electron transfer chains.
摘要：
在含氧光合系统中，细胞色素b6f（Cytb6f）复合物（Plastoquinol：plastyyanin氧化还原酶）是中心的心脏，提供了光系统（PS）II和I之间的连接。简要概述了Cytb6f复合物的结构和功能，重点研究了塑性喹醇（PQH2）的分叉（双电子）氧化机理。在植物叶绿体中，在广泛的实验条件（pH和温度）下，PQH2从PSII扩散到Cytb6f不限制系统间电子传输。PQH2转换的总体速率主要由PQH2在催化位点Qo的分叉氧化的第一步决定，即，从PQH2到高电势Rieske铁硫蛋白（ISP）的Fe2S2簇的电子转移反应。在包括ISP和周围氨基酸的Fe2S2簇的模型系统的框架内，PQH2氧化的量子化学分析支持了这一点，低电位血红素B6L，Glu78和2,3,5-三甲基苯并喹啉(PQH2的无尾类似物)。简要概述了与Cytb6f复合物相关的其他结构-功能关系和氧气光合作用的电子传输调节机制：系统间电子传输的pH依赖性控制以及线性和循环电子转移链操作之间的调节平衡。
