Zech S G, van der Est A J, Bittl R
Max-Volmer-Institut für Biophysikalische Chemie und Biochemie, Technische Universität Berlin, Germany.
Biochemistry. 1997 Aug 12;36(32):9774-9. doi: 10.1021/bi970754z.
The radical pair P700.+Q.- (P700 = primary electron donor, Q = quinone acceptor) in native photosystem I and in preparations in which the native acceptor (vitamin K1) is replaced by different quinones is investigated by pulsed EPR spectroscopy. In a two-pulse experiment, the light-induced radical pair causes an out-of-phase electron spin echo, showing an envelope modulation. From the modulation frequency, the dipolar coupling, and therefore the distance between the two cofactors, can be derived. The observation of nearly identical distances of about 25.4 A between P700.+ and Q.- in all preparations investigated here leads to the conclusion that the reconstituted quinones are bound to the native A1 binding pocket. Since the orientation of the reconstituted naphthoquinone relative to the axis joining P700.+ and Q*- differs drastically from that of the native vitamin K1, it cannot be bonded to the protein in the same way as the native acceptor. This implies that the function of A1 as an electron acceptor does not depend on the orientation or hydrogen bonding of the quinone.
利用脉冲电子顺磁共振光谱研究了天然光系统I以及其中天然受体（维生素K1）被不同醌类取代的制剂中的自由基对P700.+Q.-（P700 = 初级电子供体，Q = 醌受体）。在双脉冲实验中，光诱导的自由基对会产生异相电子自旋回波，呈现出包络调制。根据调制频率，可以推导出偶极耦合，进而得出两个辅因子之间的距离。在此研究的所有制剂中，P700.+与Q.-之间的距离均接近25.4 Å，这一观察结果得出结论：重构的醌类与天然A1结合口袋结合。由于重构的萘醌相对于连接P700.+和Q*-的轴的取向与天然维生素K1的取向有很大不同，因此它不能以与天然受体相同的方式与蛋白质结合。这意味着A1作为电子受体的功能不依赖于醌的取向或氢键。
