Hetero-oligomeric membrane protein complexes form the electron transport chain (ETC) of oxygenic photosynthesis. The ETC complexes undertake the light-driven vectorial electron and proton transport reactions, which generate energy-rich ATP and electron-rich NADPH molecules for carbon fixation. The rate of photosynthetic electron transport depends on the availability of photons and the relative abundance of electron transport complexes. The relative abundance of the two photosystems, critical for the quantum efficiency of photosynthesis in changing light quality conditions, has been determined successfully by optical methods. Due to the lack of spectroscopic signatures, however, relatively little is known about the stoichiometry of other non-photosystem complexes in plant photosynthetic membrane. Here we determine the ratios of all major thylakoid-bound ETC complexes in Arabidopsis by a label-free quantitative mass spectrometry technique. The calculated stoichiometries are consistent with known subunit composition of complexes and current estimates of photosystem and cytochrome b6f concentrations. The implications of these stoichiometries for photosynthetic light harvesting and the partitioning of electrons between the linear and cyclic electron transport pathways of photosynthesis are discussed.

中文翻译：

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植物光合膜中蛋白质复合物的化学计量。

异寡聚膜蛋白复合物形成了氧光合作用的电子传输链（ETC）。ETC络合物进行光驱动的矢量电子和质子传输反应，从而生成富能的ATP和富电子的NADPH分子用于碳固定。光合电子传输的速率取决于光子的可用性和电子传输复合物的相对丰度。这两个光系统的相对丰度，对于在变化的光质量条件下光合作用的量子效率至关重要，已通过光学方法成功确定。然而，由于缺乏光谱学特征，关于植物光合膜中其他非光系统复合物的化学计量的了解相对较少。在这里，我们通过无标记定量质谱技术确定拟南芥中所有主要类囊体结合的ETC复合物的比率。计算的化学计量与复合物的已知亚基组成以及光系统和细胞色素b6f浓度的当前估计值一致。讨论了这些化学计量对于光合作用光的收获以及光合作用的线性和循环电子传输途径之间电子分配的影响。