School of Biological Sciences, Flinders University, GPO Box 2100, 5001, Adelaide, SA, Australia.
Photosynth Res. 1994 Nov;42(2):111-20. doi: 10.1007/BF02187122.
Rate-coefficients describing the electron transfer reactions between P700 and plastocyanin, between cytochromef in cytochromebf complexes and plastocyanin, and between decyl plastoquinol and cytochromebf complexes were determined as a function of pH in the range 4-10 from flash-induced absorbancy changes at four wavelengths. The reactions between P700 and plastocyanin, and between cytochromef and plastocyanin were optimised when there was electrostatic interaction between ionised acidic groups in plastocyanin with a pKa of 4.3-4.7 and ionised basic constituents in P700 (assumed to be in the PSI-F subunit) and in cytochromef, with a pKb of 8.9-9.4. The basic groups are thought to be lysine rather than arginine. This mechanism agrees with that inferred from effects of ionic strength changes on rate-coefficients. The relation between the second-order rate-coefficient for decyl plastoquinol oxidation by thebf complex and pH was characterised by a pKa of 6.1. This is interpreted as showing that the anion radical form of that quinol, which has a pKa of 6, and which becomes progressively protonated when pH is changed from 7 to 5, is essential to reduce cytochromeb-563 (low potential) during quinol oxidation. Above pH 9, permanent effects were observed on this rate-coefficient, which were absent in the reactions between P700, plastocyanin and cytochromef.
描述 P700 与质体蓝素、细胞色素 f 在细胞色素 bf 复合物与质体蓝素、以及癸基质体醌与细胞色素 bf 复合物之间的电子传递反应的速率系数是作为 pH 值在 4-10 范围内的函数，从四个波长的闪光诱导的吸光度变化来确定的。当质体蓝素中 pKa 值为 4.3-4.7 的带电荷酸性基团与 P700（假定在 PSI-F 亚基中）和细胞色素 f 中 pKb 值为 8.9-9.4 的带电荷碱性成分之间存在静电相互作用时，P700 与质体蓝素之间以及细胞色素 f 与质体蓝素之间的反应得到优化。这些碱性基团被认为是赖氨酸而不是精氨酸。该机制与从离子强度变化对速率系数的影响推断出的机制一致。bf 复合物氧化癸基质体醌的二级速率系数与 pH 值之间的关系由 pKa 值为 6.1 来描述。这被解释为表明，该醌的阴离子自由基形式具有 pKa 值为 6，并且当 pH 值从 7 变为 5 时，它会逐渐质子化，这对于在醌氧化过程中还原细胞色素 b-563（低电位）是必不可少的。在 pH 值高于 9 时，观察到该速率系数的永久性影响，而在 P700、质体蓝素和细胞色素 f 之间的反应中则不存在这种影响。
