Cyanobacterial photosynthetic systems efficiently capture sunlight using the pigment-protein megacomplexes, phycobilisome (PBS). The energy is subsequently transferred to photosystem I (PSI) and II (PSII), to produce electrochemical potentials. In the present study, we performed picosecond (ps) time-resolved fluorescence and femtosecond (fs) pump-probe spectroscopies on the intact PBS from a thermophilic cyanobacterium, Thermosynechococcus vulcanus, to reveal excitation energy transfer dynamics in PBS. The photophysical properties of the intact PBS were well characterized by spectroscopic measurements covering wide temporal range from femtoseconds to nanoseconds. The ps fluorescence measurements excited at 570 nm, corresponding to the higher energy of the phycocyanin (PC) absorption band, demonstrated the excitation energy transfer from the PC rods to the allophycocyanin (APC) core complex as well as the energy transfer in the APC core complex. Then, the fs pump-probe measurements revealed the detailed energy transfer dynamics in the PC rods taking place in an ultrafast time scale. The results obtained in this study provide the full picture of the funnel-type excitation energy transfer with rate constants of (0.57 ps)⁻¹ → (7.3 ps)⁻¹ → (53 ps)⁻¹ → (180 ps)⁻¹ → (1800 ps)⁻¹.

蓝藻光合系统使用色素-蛋白质巨型复合物藻胆体 (PBS) 有效地捕获阳光。能量随后转移到光系统 I (PSI) 和 II (PSII)，以产生电化学势。在本研究中，我们对来自高温蓝细菌Thermosynechococcus vulcanus的完整 PBS 进行了皮秒 (ps) 时间分辨荧光和飞秒 (fs) 泵浦探针光谱, 揭示 PBS 中的激发能量转移动力学。完整 PBS 的光物理特性通过光谱测量得到了很好的表征，涵盖了从飞秒到纳秒的宽时间范围。在 570 nm 激发的 ps 荧光测量值对应于藻蓝蛋白 (PC) 吸收带的更高能量，证明了从 PC 棒到别藻蓝蛋白 (APC) 核心复合物的激发能量转移以及 APC 核心中的能量转移复杂的。然后，fs 泵-探针测量揭示了在超快时间尺度内发生的 PC 棒中详细的能量转移动力学。本研究中获得的结果提供了漏斗型激发能量转移的全貌，速率常数为 (0.57 ps) ^-1  → (7.3 ps) ^-1 → (53 ps) ^-1  → (180 ps) ^-1  → (1800 ps) ^-1。