Temperature-dependent energy gap of the primary charge separation in photosystem I: study of delayed fluorescence at 77-268 K.
The dynamics of fluorescence decay and charge recombination were studied in the ether-extracted photosystem I reaction center isolated from spinach with picosecond resolution over a wide time range up to 100 ns. At all temperatures from 268 to 77 K, a slow fluorescence decay component with a 30-40 ns lifetime was detected. This component was interpreted as a delayed fluorescence emitted from the singlet excited state of the primary donor P700*, which is repopulated through charge recombination that was increased by the lack of secondary acceptor phylloquinone in the sample. Analysis of the fluorescence kinetics allowed estimation of the standard free-energy difference -DeltaG between P700* and the primary radical pair (P700(+)A0(-)) state over a wide temperature range. The values of -DeltaG were estimated to be 160/36 meV at 268/77 K, indicating its high sensitivity to temperature. A temperature-dependent -DeltaG value was also estimated in the delayed fluorescence of the isolated photosystem I in which the secondary acceptor quinone was partially prereduced by preillumination in the presence of dithionite. The results revealed that the temperature-dependent -DeltaG is a universal phenomenon common with the purple bacterial reaction centers, photosystem II and photosystem I reaction centers.
Shibata
Yutaka
Y
Division of Material Science (Physics), Graduate School of Science, Nagoya University, Nagoya 464-8602, Japan. yshibata@bio.phys.nagoya-u.ac.jp
Akai
Shinpei
S
Kasahara
Takashi
T
Ikegami
Isamu
I
Itoh
Shigeru
S
D003080:Cold Temperature; D005453:Fluorescence; D007700:Kinetics; D045331:Photosystem I Protein Complex / Q000737:chemistry*; D013696:Temperature
D045331:Photosystem I Protein Complex