Abstract
Phytochromes' ring D orientational changes are tracked during Z-to-E photoisomerization by polarization resolved femtosecond visible pump-infrared probe spectroscopy. Two distinct Pr isoforms Pr-I and Pr-II exhibit photoisomerization yields of 3% and 29%, respectively.
Highlights
Photoisomerization of the phycocyanobilin (PCB) chromophore is the basis of the light sensing and signaling response of Cph1 phytochrome
Excitation of the Pr form with ZZZssa (C5-Z, C10-Z, C15-Z, C5-syn, C10-syn, C15-anti)[2] PCB chromophore geometry initiates an ultrafast Z-toE photoisomerization of phytochromes’ ring D around C15=C16 methine bridge resulting in the Lumi-R photoproduct
We used polarization resolved femtosecond visible pump-infrared probe spectroscopy to determine the orientation of the v(C=O) vibrational modes of the PCB chromophore on a femtosecond time scale in the Pr* and Pr state.[6]
Summary
Photoisomerization of the phycocyanobilin (PCB) chromophore is the basis of the light sensing and signaling response of Cph phytochrome. Phytochromes are a family of dimeric chromoproteins that absorb light and regulate numerous photoresponses in plants, bacteria, and fungi.[1] Two thermally stable ground states conformers sensing red (Pr form) and far-red light (Pfr form) can be interconverted by photoexcitation. Two time constants of about 3 ps to 16 ps and 25 ps to 40 ps are reported for the initial processes.[3] The low photoproduct quantum yield of 7% to 16% in phytochromes was proposed to result from photoreceptor heterogeneities.[4] Recently, two Pr isoforms were identified by NMR spectroscopy.[5]
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