Department of Chemistry and The James Franck Institute, University of Chicago, Chicago, IL 60637, USA.
Proc Natl Acad Sci U S A. 2010 Jul 20;107(29):12766-70. doi: 10.1073/pnas.1005484107. Epub 2010 Jul 6.
Photosynthetic antenna complexes capture and concentrate solar radiation by transferring the excitation to the reaction center that stores energy from the photon in chemical bonds. This process occurs with near-perfect quantum efficiency. Recent experiments at cryogenic temperatures have revealed that coherent energy transfer--a wave-like transfer mechanism--occurs in many photosynthetic pigment-protein complexes. Using the Fenna-Matthews-Olson antenna complex (FMO) as a model system, theoretical studies incorporating both incoherent and coherent transfer as well as thermal dephasing predict that environmentally assisted quantum transfer efficiency peaks near physiological temperature; these studies also show that this mechanism simultaneously improves the robustness of the energy transfer process. This theory requires long-lived quantum coherence at room temperature, which never has been observed in FMO. Here we present evidence that quantum coherence survives in FMO at physiological temperature for at least 300 fs, long enough to impact biological energy transport. These data prove that the wave-like energy transfer process discovered at 77 K is directly relevant to biological function. Microscopically, we attribute this long coherence lifetime to correlated motions within the protein matrix encapsulating the chromophores, and we find that the degree of protection afforded by the protein appears constant between 77 K and 277 K. The protein shapes the energy landscape and mediates an efficient energy transfer despite thermal fluctuations.
光合作用天线复合物通过将激发转移到反应中心来捕获和集中太阳能，反应中心将光子的能量储存在化学键中。这个过程的量子效率接近完美。最近在低温下的实验表明，在许多光合色素 - 蛋白质复合物中发生相干能量转移 - 一种波状转移机制。使用 Fenna-Matthews-Olson 天线复合物（FMO）作为模型系统，将非相干和相干转移以及热去相位都包含在内的理论研究预测，环境辅助量子转移效率在生理温度附近达到峰值; 这些研究还表明，这种机制同时提高了能量转移过程的稳健性。该理论要求室温下存在长寿命的量子相干性，但在 FMO 中从未观察到。在这里，我们提供的证据表明，量子相干性在生理温度下至少在 FMO 中持续 300fs，足以影响生物能量传递。这些数据证明在 77K 下发现的波状能量转移过程与生物功能直接相关。从微观上看，我们将这种长相干寿命归因于包裹发色团的蛋白质基质内的相关运动，并且我们发现蛋白质提供的保护程度在 77K 和 277K 之间保持不变。蛋白质塑造了能量景观，并介导了尽管存在热波动但仍有效的能量转移。
