title: Temperature-dependent energy gap of the primary charge separation in photosystem I: study of delayed fluorescence at 77-268 K.
abstract: 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.
authors.affiliation: Division of Material Science (Physics), Graduate School of Science, Nagoya University, Nagoya 464-8602, Japan. yshibata@bio.phys.nagoya-u.ac.jp
authors.forename: Yutaka
authors.initials: Y
authors.lastname: Shibata
authors.forename: Shinpei
authors.initials: S
authors.lastname: Akai
authors.forename: Takashi
authors.initials: T
authors.lastname: Kasahara
authors.forename: Isamu
authors.initials: I
authors.lastname: Ikegami
authors.forename: Shigeru
authors.initials: S
authors.lastname: Itoh
mesh_terms: D003080:Cold Temperature; D005453:Fluorescence; D007700:Kinetics; D045331:Photosystem I Protein Complex / Q000737:chemistry*; D013696:Temperature
chemical_list: D045331:Photosystem I Protein Complex