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Time‐Resolved Energetics of Photoprocesses in Prokaryotic Phytochrome‐Related Photoreceptors
Author(s) -
Losi Aba,
Bonomi Hernán R.,
Michael Norbert,
Tang Kun,
Zhao KaiHong
Publication year - 2017
Publication title -
photochemistry and photobiology
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.818
H-Index - 131
eISSN - 1751-1097
pISSN - 0031-8655
DOI - 10.1111/php.12728
Subject(s) - photoisomerization , phytochrome , chromophore , chemistry , photochemistry , photochromism , synechocystis , isomerization , quantum yield , biophysics , red light , physics , botany , mutant , optics , biology , catalysis , biochemistry , gene , fluorescence
Abstract Time‐resolved photoacoustics ( PA ) is uniquely able to explore the energy landscape of photoactive proteins and concomitantly detects light‐induced volumetric changes (Δ V ) accompanying the formation and decay of transient species in a time window between ca. 20 ns and 5 μ s. Here, we report PA measurements on diverse photochromic bilin‐binding photoreceptors of prokaryotic origin: (1) the chromophore‐binding GAF 3 domain of the red (R)/green (G) switching cyanobacteriochrome 1393 ( Slr 1393g3) from Synechocystis ; (2) the red/far red (R/ FR ) Synechocystis Cph1 phytochrome; (3) full‐length and truncated constructs of Xanthomonas campestris bacteriophytochrome ( Xcc BphP), absorbing up to the NIR spectral region. In almost all cases, photoisomerization results in a large fraction of energy dissipated as heat (up to 90%) on the sub‐ns scale, reflecting the low photoisomerization quantum yield (<0.2). This “prompt” step is accompanied by a positive Δ V 1 = 5–12.5 mL mol −1 . Formation of the first intermediate is the sole process accessible to PA , with the notable exception of Slr 1393g3‐G for which Δ V 1 = +4.5 mL mol −1 is followed by a time‐resolved, energy‐conserving contraction Δ V 2 = −11.4 mL mol −1 , τ 2 = 180 ns at 2.4°C. This peculiarity is possibly due to a larger solvent occupancy of the chromophore cavity for Slr 1393g3‐G.