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. Author manuscript; available in PMC: 2021 Aug 30.
Published in final edited form as: Structure. 2021 Mar 22;29(7):743–754.e4. doi: 10.1016/j.str.2021.03.004

Figure 2. Phytochrome photocycle and UV-visible absorption spectra of SaBphP2.

Figure 2.

(A) Phytochrome photocycle. Approximate time scales for intermediate (Lumi-R, Meta-Ra, and Meta-Rc) formation are shown. Pfr is formed after about 50 ms with variations between different BphPs. The two half cycles can be driven by illuminating the stable Pr and Pfr states (displayed for the SaBphP2 and DrBphP PCMs, respectively) by red and far-red light.

(B) The chemical structure of BV bound to Cys13 in the phytochrome. The torsional angle ϕ⊤ that defines isomerization/rotation about the double bond Δ15,16 is indicated. In Pr the structure is all-Z syn-syn-anti.

(C) Static absorption spectra of the SaBphP2 Pr (solid line) to Pfr (dashed line) transition in solution. The difference is shown in red.

(D) As (C) but in the crystal. The transition is initiated by 640 nm LED light (arrow). The difference (red line) is enhanced 3-fold.