Kirpich Julia S, Mix L Tyler, Martin Shelley S, Rockwell Nathan C, Lagarias J Clark, Larsen Delmar S
Department of Chemistry , University of California, Davis , One Shields Avenue , Davis 95616 , California , United States.
Department of Molecular and Cell Biology , University of California, Davis , One Shields Avenue , Davis , California 95616 , United States.
J Phys Chem Lett. 2018 Jun 21;9(12):3454-3462. doi: 10.1021/acs.jpclett.8b01133. Epub 2018 Jun 11.
Phytochrome proteins utilize ultrafast photoisomerization of a linear tetrapyrrole chromophore to detect the ratio of red to far-red light. Femtosecond photodynamics in the PAS-GAF-PHY photosensory core of the Cph1 phytochrome from Synechocystis sp. PCC6803 (Cph1Δ) were resolved with a dual-excitation-wavelength-interleaved pump-probe (DEWI) approach with two excitation wavelengths (600 and 660 nm) at three pH values (6.5, 8.0, and 9.0). Observed spectral and kinetic heterogeneity in the excited-state dynamics were described with a self-consistent model comprised of three spectrally distinct populations with different protonation states (P-I, P-II, and P-III), each composed of multiple kinetically distinct subpopulations. Apparent partitioning among these populations is dictated by pH, temperature, and excitation wavelength. Our studies provide insight into photocycle initiation dynamics at physiological temperatures, implicate the low-pH/low-temperature P-I state as the photoactive state in vitro, and implicate an internal hydrogen-bonding network in regulating the photochemical quantum yield.
光敏色素蛋白利用线性四吡咯生色团的超快光异构化来检测红光与远红光的比例。采用双激发波长交错泵浦探测（DEWI）方法，在三个pH值（6.5、8.0和9.0）下，使用两个激发波长（600和660 nm）解析了来自集胞藻PCC6803（Cph1Δ）的Cph1光敏色素的PAS-GAF-PHY光感核心中的飞秒光动力学。用一个自洽模型描述了激发态动力学中观察到的光谱和动力学异质性，该模型由三个具有不同质子化状态（P-I、P-II和P-III）的光谱不同的群体组成，每个群体由多个动力学不同的亚群体组成。这些群体之间的表观分配取决于pH值、温度和激发波长。我们的研究深入了解了生理温度下的光循环起始动力学，表明低pH/低温P-I状态是体外的光活性状态，并表明内部氢键网络在调节光化学量子产率中起作用。
