Höök F, Brzezinski P
Department of Biochemistry and Biophysics, University of Göteborg, Sweden.
Biophys J. 1994 Jun;66(6):2066-72. doi: 10.1016/S0006-3495(94)81001-X.
We have measured light-induced voltage changes (electrogenic events) in photosystem II (PSII) core complexes oriented in phospholipid monolayers. These events are compared to those measured in the functionally and structurally closely related reaction centers from the photosynthetic bacterium Rhodobacter sphaeroides. In both systems we observed a rapid (< 100 ns) light-induced increase in voltage associated with charge separation. In PSII reaction centers it was followed by a decrease (decay) of approximately 14% of the charge-separation voltage and a time constant of approximately 500 microseconds. In bacterial reaction centers this decay was approximately 9% of the charge-separation voltage, and the time constant was approximately 200 microseconds. The decay was presumably associated with a structural change. In bacterial reaction centers, in the presence of excess water-soluble cytochrome c2+, it was followed by a slower increase of approximately 30% of the charge-separation voltage, associated with electron transfer from the cytochrome to the oxidized donor, P+. In PSII reaction centers, after the decay the voltage remained on the same level for > or = 0.5 s. In PSII reaction centers the electron transfer Q-AQB-->QA Q-B contributed with an electrogenicity of < or = 5% of that of the charge separation. In bacterial reaction centers this electrogenicity was < or = 2% of the charge-separation electrogenicity. Proton transfer to Q2-B in PSII reaction centers contributed with approximately 5% of the charge-separation voltage, which is approximately a factor of three smaller than that observed in bacterial reaction centers.
我们测量了取向于磷脂单层中的光系统II（PSII）核心复合物中的光诱导电压变化（电致事件）。将这些事件与在光合细菌球形红杆菌功能和结构密切相关的反应中心中测量的事件进行比较。在这两个系统中，我们都观察到与电荷分离相关的光诱导电压快速（<100纳秒）增加。在PSII反应中心，随后电荷分离电压下降（衰减）约14%，时间常数约为500微秒。在细菌反应中心，这种衰减约为电荷分离电压的9%，时间常数约为200微秒。这种衰减可能与结构变化有关。在细菌反应中心，在存在过量水溶性细胞色素c2+的情况下，随后电荷分离电压缓慢增加约30%，这与电子从细胞色素转移到氧化供体P+有关。在PSII反应中心，衰减后电压在>或=0.5秒内保持在同一水平。在PSII反应中心，电子转移Q-AQB-->QA Q-B的电致性小于或等于电荷分离电致性的5%。在细菌反应中心，这种电致性小于或等于电荷分离电致性的2%。PSII反应中心中质子转移到Q2-B的贡献约为电荷分离电压的5%，这比在细菌反应中心观察到的约小三倍。
