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EVIDENCE FOR A SEQUENTIAL PATHWAY FROM P r TO P fr OF THE PHOTOTRANSFORMATION OF 124‐kDa OAT PHYTOCHROME
Author(s) -
Eilfeld Peter,
Eilfeld Petra,
Vogel Jürgen,
Maurer Robert
Publication year - 1987
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/j.1751-1097.1987.tb07890.x
Subject(s) - absorbance , reaction rate constant , phytochrome , chemistry , kinetics , relaxation (psychology) , molar absorptivity , analytical chemistry (journal) , absorption (acoustics) , extinction (optical mineralogy) , wavelength , photochemistry , physics , chromatography , optics , red light , biology , mineralogy , quantum mechanics , botany , neuroscience
. Phototransformation kinetics of 124‐kDa oat phytochrome at 298 K after a red (660‐nm) laser flash excitation were recorded at different wavelengths. The kinetics of the dark relaxation processes for lumi‐R to P fr can be satisfactorily described by only 3 rate constants: k = 28000 s ‐1 370 s ‐1 and 20 s ‐1 . The first rate constant is due to the decay of lumi‐R to meta ‐Ra. The latter two rate constants correspond to processes establishing the far‐red (>700 nm) absorption band. No meta ‐Rb could be detected. From the wavelength dependency of the amplitudes of these two rates, parallel pathways in the formation of P fr could be excluded. A unique sequential pathway for the dark relaxation leading to P fr seems to be an intrinsic property of 124‐kDa phytochrome, however. Assuming a sequential pathway, molar extinction coefficients for intermediates have been calculated. These values agree with molar extinction coefficients obtained from low‐temperature spectra. The process with a rate constant of 370 s ‐1 corresponds to absorbance changes for the formation of meta ‐Rc from meta ‐Ra and the rate constant of 20 s ‐1 describes the absorbance changes due to the transformation of meta ‐Rc to P fr.