Photosystem I core-light-harvesting antenna supercomplexes (PSI-LHCI) were isolated from the extremophilic red alga Cyanidioschyzon merolae and studied by three fluorescence techniques in order to characterize chlorophylls (Chls) energetically uncoupled from the PSI reaction center (RC). Such Chls are observed in virtually all optical experiments of any PSI core and PSI-LHCI supercomplex preparations across various species and may influence the operation of PSI-based solar cells and other biohybrid systems. However, the nature of the uncoupled Chls (uChls) has never been explored deeply before. In this work, the amount of uChls was controlled by stirring the solution of C. merolae PSI-LHCI supercomplex samples at elevated temperature (~303 K) and was found to increase from <2% in control samples up to 47% in solutions stirred for 3.5 h. The fluorescence spectrum of uChls was found to be blue-shifted by ~20 nm (to ~680 nm) relative to the fluorescence band from Chls that are well coupled to PSI RC. This effect indicates that mechanical stirring leads to disappearance of some red Chls (emitting at above ~700 nm) that are present in the intact LHCI antenna associated with the PSI core. Comparative diffusion studies of control and stirred samples by fluorescence correlation spectroscopy together with biochemical analysis by SDS-PAGE and BN-PAGE indicate that energetically uncoupled Lhcr subunits are likely to be still physically attached to the PSI core, albeit with altered three-dimensional organization due to the mechanical stress.

中文翻译：

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关于极端的光系统中未耦合的叶绿素的性质I-光捕获I超复杂。

从极端嗜热的红藻Cyanidioschyzon merolae中分离出光系统I核心光收集天线超复合物（PSI-LHCI），并通过三种荧光技术进行研究，以表征与PSI反应中心（RC）能量上不耦合的叶绿素（Chls）。实际上，在各种物种的任何PSI核心和PSI-LHCI超复合制剂的所有光学实验中均会观察到这种Chls，并且可能会影响基于PSI的太阳能电池和其他生物混合系统的运行。但是，未耦合的Chls（uChls）的性质以前从未被深入探讨过。在这项工作中，uChls的量是通过在高温（〜303 K）下搅拌棒状弯曲杆菌PSI-LHCI超复杂样品的溶液来控制的，发现其从对照样品中的<2％增加到搅拌溶液中的47％持续3.5小时。发现uChls的荧光光谱相对于与PSI RC良好耦合的Chls的荧光带发生了约20 nm（约680 nm）的蓝移。这种效果表明，机械搅拌会导致一些红色的Chl消失（在〜700 nm以上发射），这些红色的Chl消失在与PSI核心相关的完整LHCI天线中。通过荧光相关光谱对对照样品和搅拌样品的扩散研究以及通过SDS-PAGE和BN-PAGE进行的生化分析表明，尽管由于三维结构的改变，能量上未偶联的Lhcr亚基仍可能物理附着在PSI核上机械应力。