Lee J W, Lee I, Laible P D, Owens T G, Greenbaum E
Oak Ridge National Laboratory, Tennessee 37831-6194, USA.
Biophys J. 1995 Aug;69(2):652-9. doi: 10.1016/S0006-3495(95)79941-6.
Isolated photosystem I (PSI) reaction center/core antenna complexes (PSI-40) were platinized by reduction of [PtCl6]2- at 20 degrees C and neutral pH. PSI particles were visualized directly on a gold surface by scanning tunneling microscopy (STM) before and after platinization. STM results showed that PSI particles were monomeric and roughly ellipsoidal with major and minor axes of 6 and 5 nm, respectively. Platinization deposited approximately 1000 platinum atoms on each PSI particle and made the average size significantly larger (9 x 7 nm). In addition to direct STM visualization, the presence of metallic platinum on the PSI complexes was detected by its effect of actinic shading and electrostatic shielding on P700 photooxidation and P700+ reduction. The reaction centers (P700) in both platinized and nonplatinized PSI-40 were photooxidized by light and reduced by ascorbate repeatedly, although at somewhat slower rates in platinized PSI because of the presence of platinum. The effect of platinization on excitation transfer and trapping dynamics was examined by measuring picosecond fluorescence decay kinetics in PSI-40. The fluorescence decay kinetics in both platinized and control samples can be described as a sum of three exponential components. The dominant (amplitude 0.98) and photochemically limited excitation lifetime remained the same (16 ps) before and after platinization. The excitation transfer and trapping in platinized PSI-40 was essentially as efficient as that in the control (without platinization) PSI. The platinization also did not affect the intermediate-lifetime (400-600 ps) and long-lifetime (> 2500 ps) components, which likely are related to intrinsic electron transport and to functionally uncoupled chlorophylls, respectively. The amplitudes of these two components were exceptionally small in both of the samples. These results provide direct evidence that although platinization dramatically alters the photocatalytic properties of PSI, it does not alter the intrinsic excitation dynamics and initial electron transfer reactions in PSI.
通过在20℃和中性pH条件下还原[PtCl6]2-，对分离的光系统I（PSI）反应中心/核心天线复合物（PSI-40）进行铂化处理。在铂化处理前后，通过扫描隧道显微镜（STM）直接观察金表面上的PSI颗粒。STM结果表明，PSI颗粒为单体，大致呈椭圆形，长轴和短轴分别为6纳米和5纳米。铂化处理在每个PSI颗粒上沉积了约1000个铂原子，使平均尺寸显著增大（9×7纳米）。除了直接的STM观察外，还通过其对P700光氧化和P700+还原的光化遮光和静电屏蔽作用，检测了PSI复合物上金属铂的存在。铂化和未铂化的PSI-40中的反应中心（P700）均被光反复光氧化并被抗坏血酸还原，不过由于铂的存在，铂化的PSI中反应速率稍慢。通过测量PSI-40中的皮秒荧光衰减动力学，研究了铂化对激发转移和俘获动力学的影响。铂化样品和对照样品中的荧光衰减动力学均可描述为三个指数成分的总和。铂化前后，占主导地位（振幅0.98）且受光化学限制的激发寿命保持不变（16皮秒）。铂化的PSI-40中的激发转移和俘获基本上与对照（未铂化）PSI中的效率相同。铂化处理也不影响中间寿命（400 - 600皮秒）和长寿命（>2500皮秒）成分，这两个成分可能分别与内在电子传递和功能上未偶联的叶绿素有关。这两个成分的振幅在两个样品中都异常小。这些结果提供了直接证据，表明尽管铂化显著改变了PSI的光催化性质，但它并未改变PSI中的内在激发动力学和初始电子转移反应。
