Kinetics of Reactions Around the Cytochrome bf Complex Studied in Intact Leaf Disks
Kinetics of Reactions Around the Cytochrome bf Complex Studied in Intact Leaf Disks
复制标题
在完整叶盘中研究的细胞色素 bf 复合物周围反应动力学
作者：
Wah Soon Chow;A. Hope
通过测量特定波长下闪光引起的吸光度变化，研究了几种植物物种叶子中光合电子传递链（包括细胞色素 (cyt) bf 和光系统 (PS) I 复合物）中的电子传递。电致变色信号 (ECS) 表示跨类囊体膜电场，由两个光系统中电荷分离产生的快速相和通常解释为 cyt bf 复合体（Q 循环的一部分）中的电荷转移的缓慢上升相组成。 ECS 慢相的幅度通常大于 PS I 中氧化的 P700 通过质体蓝素 (PC) 从 cyt bf 撤回电子所能解释的幅度。“额外的”慢 ECS，根据周转次数和植物种类而变化，可归因于 cyt bf 复合物的质子泵浦活性的可变操作。细胞色素 f 和 b 的氧化还原动力学通过三个或四个波长的信号去卷积获得。 cyt b 的减少率非常高，并且与慢速 ECS 的起始动力学不同。细胞色素 f 信号表明，氧化细胞色素 f 的一部分仅在连续闪光之间的 5 秒时间内缓慢地重新还原。在远红光下对叶盘进行单周转闪光以测量 P700ox 还原和再氧化的速率。为了模拟 ECS、cyt f、cyt b 和 P700 的氧化还原动力学，假设 Q 循环通常在 bf 复合物中运行；选择了适当的速率系数以及 cyt f/PC 和 P700/PC 反应的平衡常数的合理值。对于 cyt b、P700（远红光实验）和 ECS，观察到的数据与模拟预测的数据非常相似，但对于 cyt f 则不然。这些结果有助于了解体内光合作用电子转移。
Electron transfers in the photosynthetic electron transport chain including the cytochrome (cyt) bf and Photosystem (PS) I complexes were studied in leaves of several plant species by measuring flash-induced absorbancy changes at specific wavelengths. The electrochromic signal (ECS), indicative of a trans-thylakoid membrane electric field, consisted of a fast phase arising from charge separation in both photosystems, and a slow rise usually interpreted as charge transfer in the cyt bf complex (part of the Q-cycle). The amplitude of the slow phase of the ECS was frequently greater than could be accounted for by the withdrawal of an electron from cyt bf via plastocyanin (PC) by oxidised P700 in PS I. The ‘extra’ slow ECS, variable depending on the number of turnovers and plant species, can be attributed to a variable operation of proton-pumping activity of the cyt bf complex. The redox kinetics of cyt f and b were obtained by deconvolution of the signals at three or four wavelengths. Rates of cyt b reduction were very high, and never the same as the onset kinetics of the slow ECS. The cyt f signal suggests that a fraction of the oxidised cyt f was re-reduced only slowly in the time of 5 s between consecutive flashes. Leaf discs in far-red light were given single-turnover flashes to measure the rates of P700ox reduction and reoxidation. To simulate the redox kinetics of the ECS, cyt f, cyt b and P700 it was assumed that a Q-cycle normally operated in bf complexes; reasonable values for the appropriate rate coefficients, and for the equilibrium constants for the cyt f/PC and P700/PC reactions were chosen. Close similarity of the observed data with those predicted from the simulation was obtained for cyt b, P700 (far-red light experiments) and the ECS, but not for cyt f. The results contribute to an understanding of photosynthetic electron transfers in vivo.
叶绿体细胞色素f消光系数的批判性分析。
DOI：
10.1016/s0005-2728(96)00164-8
发表时间：
1997
期刊：
Biochimica et biophysica acta
影响因子：
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作者：
Metzger,SU;Cramer,WA;Whitmarsh,J
通讯作者：
Whitmarsh,J