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首页> 美国卫生研究院文献>Proceedings of the National Academy of Sciences of the United States of America >Determination of the primary charge separation rate in isolated photosystem II reaction centers with 500-fs time resolution
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Determination of the primary charge separation rate in isolated photosystem II reaction centers with 500-fs time resolution

机译：以500 fs的时间分辨率确定孤立的光系统II反应中心中的一次电荷分离率

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摘要

We have measured directly the rate of formation of the oxidized chlorophyll a electron donor (P680+) and the reduced electron acceptor pheophytin a- (Pheoa-) following excitation of isolated spinach photosystem II reaction centers at 4°C. The reaction-center complex consists of D1, D2, and cytochrome b-559 proteins and was prepared by a procedure that stabilizes the protein complex. Transient absorption difference spectra were measured from 440 to 850 nm as a function of time with 500-fs resolution following 610-nm laser excitation. The formation of P680+-Pheoa- is indicated by the appearance of a band due to P680+ at 820 nm and corresponding absorbance changes at 505 and 540 nm due to formation of Pheoa-. The appearance of the 820-nm band is monoexponential with τ = 3.0 ± 0.6 ps. The time constant for decay of 1*P680, the lowest excited singlet state of P680, monitored at 650 nm, is τ = 2.6 ± 0.6 ps and agrees with that of the appearance of P680+ within experimental error. Treatment of the photosystem II reaction centers with sodium dithionite and methyl viologen followed by exposure to laser excitation, conditions known to result in accumulation of Pheoa-, results in formation of a transient absorption spectrum due to 1*P680. We find no evidence for an electron acceptor that precedes the formation of Pheoa-.
机译：我们直接测量了氧化的叶绿素a电子供体（P680 + ）和还原的电子受体脱镁叶绿素a -（Pheoa - >）在4°C下激发孤立的菠菜光系统II反应中心。反应中心复合物由D1，D2和细胞色素b-559蛋白组成，并通过稳定蛋白质复合物的程序制备。在610 nm激光激发之后，以500-fs的分辨率测量了440至850 nm随时间变化的瞬态吸收差光谱。 P680 + -Pheoa -的形成由在820 nm处由于P680 + 引起的谱带出现以及在505处的相应吸光度变化指示由于形成了Pheoa -而产生了540 nm。 820 nm波段的出现是单指数的，τ= 3.0±0.6 ps。 1 * P680的衰减时间常数（在650 nm处监测的P680的最低激发单重态）为τ= 2.6±0.6 ps，与P680 +的出现时间一致出现实验错误。用连二亚硫酸钠和甲基紫精处理光系统II反应中心，然后暴露于激光激发（已知会导致Pheoa -积累的条件），由于 1 * P680。我们没有发现在Pheoa -形成之前存在电子受体的证据。

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