Kirchhoff H, Horstmann S, Weis E
Institut für Botanik, Münster, Germany.
Biochim Biophys Acta. 2000 Jul 20;1459(1):148-68. doi: 10.1016/s0005-2728(00)00143-2.
We investigate the role of plastoquinone (PQ) diffusion in the control of the photosynthetic electron transport. A control analysis reveals an unexpected flux control of the whole chain electron transport by photosystem (PS) II. The contribution of PSII to the flux control of whole chain electron transport was high in stacked thylakoids (control coefficient, CJ(PSII) =0.85), but decreased after destacking (CJ(PSII)=0.25). From an 'electron storage' experiment, we conclude that in stacked thylakoids only about 50 to 60% of photoreducable PQ is involved in the light-saturated linear electron transport. No redox equilibration throughout the membrane between fixed redox groups at PSII and cytochrome (cyt) bf complexes, and the diffusable carrier PQ is achieved. The data support the PQ diffusion microdomain concept by Lavergne et al. [J. Lavergne, J.-P. Bouchaud, P. Joliot, Biochim. Biophys. Acta 1101 (1992) 13-22], but we come to different conclusions about size, structure and size distribution of domains. From an analysis of cyt b6 reduction, as a function of PSII inhibition, we conclude that in stacked thylakoids about 70% of PSII is located in small domains, where only 1 to 2 PSII share a local pool of a few PQ molecules. Thirty percent of PSII is located in larger domains. No small domains were found in destacked thylakoids. We present a structural model assuming a hierarchy of specific, strong and weak interactions between PSII core, light harvesting complexes (LHC) II and cyt bf. Peripheral LHCII's may serve to connect PSII-LHCII supercomplexes to a flexible protein network, by which small closed lipid diffusion compartments are formed. Within each domain, PQ moves rapidly and shuttles electrons between PSII and cyt bf complexes in the close vicinity. At the same time, long range diffusion is slow. We conclude, that in high light, cyt bfcomplexes located in distant stromal lamellae (20 to 30%) are not involved in the linear electron transport.
我们研究了质体醌（PQ）扩散在光合电子传递控制中的作用。控制分析揭示了光系统（PS）II对整个链电子传递的意外通量控制。在堆叠类囊体中，PSII对整个链电子传递通量控制的贡献较高（控制系数，CJ(PSII)=0.85），但去堆叠后降低（CJ(PSII)=0.25）。通过“电子储存”实验，我们得出结论，在堆叠类囊体中，只有约50%至60%的可光还原PQ参与光饱和线性电子传递。PSII和细胞色素（cyt）bf复合物处的固定氧化还原基团与可扩散载体PQ之间在整个膜中未实现氧化还原平衡。这些数据支持了Lavergne等人提出的PQ扩散微区概念[J. Lavergne, J.-P. Bouchaud, P. Joliot, Biochim. Biophys. Acta 1101 (1992) 13 - 22]，但我们对微区的大小、结构和大小分布得出了不同结论。通过分析作为PSII抑制函数的cyt b6还原，我们得出结论，在堆叠类囊体中，约70%的PSII位于小区域，其中只有1至2个PSII共享少量PQ分子的局部池。30%的PSII位于较大区域。在去堆叠类囊体中未发现小区域。我们提出了一个结构模型，假设PSII核心、捕光复合物（LHC）II和cyt bf之间存在特定、强和弱相互作用的层次结构。外周LHCII可能用于将PSII - LHCII超复合物连接到一个灵活的蛋白质网络，由此形成小的封闭脂质扩散隔室。在每个区域内，PQ快速移动并在附近的PSII和cyt bf复合物之间穿梭电子。同时，长距离扩散缓慢。我们得出结论，在高光下，位于远处基质片层（20%至30%）的cyt bf复合物不参与线性电子传递。
