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_r-I, P_r-II, and P_r-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_r-I state as the photoactive state in vitro, and implicate an internal hydrogen-bonding network in regulating the photochemical quantum yield.

中文翻译：

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质子异质性调节植物色素Cph1的超快光周期引发动力学。

植物色素蛋白利用线性四吡咯发色团的超快光异构化来检测红光与远红光的比率。飞蛾光动力学在Synechocystis sp。的Cph1植物色素的PAS-GAF-PHY光感官核心中。PCC6803（Cph1Δ）通过双激发波长交错泵浦-探针（DEWI）方法得到解析，在三个pH值（6.5、8.0和9.0）下具有两个激发波长（600和660 nm）。用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态（P _r -I，P _r -II和P _r的光谱不同的种群）组成-III），每个由多个动力学上不同的亚群组成。这些种群之间的表观分配是由pH，温度和激发波长决定的。我们的研究提供了在生理温度下光周期引发动力学的见解，将低pH /低温P _r -I状态暗示为体外的光活性状态，并暗示了内部氢键网络调节光化学量子产率。