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Analysis of the electron transfer from Pheo − to Q A in PS II membrane fragments from spinach by time resolved 325 nm absorption changes in the picosecond domain
Author(s) -
Eckert H.-J.,
Wiese N.,
Bernarding J.,
Eichler H.-J.,
Renger G.
Publication year - 1988
Publication title -
febs letters
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.593
H-Index - 257
eISSN - 1873-3468
pISSN - 0014-5793
DOI - 10.1016/0014-5793(88)80358-2
Subject(s) - picosecond , chemistry , absorption (acoustics) , time constant , analytical chemistry (journal) , electron transfer , kinetics , excitation , atomic physics , laser , optics , photochemistry , physics , electrical engineering , chromatography , quantum mechanics , engineering
Absorption changes at 325 nm (Δ A 325 ) induced by 15 ps laser flashes (λ = 650 nm) in PS II membrane fragments were measured with picosecond time‐resolution. In samples with the reaction centers (RCs) kept in the open state (P I Q A ) the signals are characterized by a very fast rise (not resolvable by our equipment) followed by only small changes within our time window of 1.6 ns. In the closed state (P I Q − A ) of the reaction center the signal decays with an average half‐life time of about 250 ps. It is shown that under our excitation conditions ( E = 2 × 10 14 photons/cm 2 per pulse) subtraction of the absorption changes in closed RCs (Δ A closed 325 ) from those in open RCs (Δ A open 325 ) leads to a difference signal which is dominated by the reduction kinetics of Q A . From the rise kinetics of this signal and by comparison with data in the literature it is inferred that Q A becomes reduced by direct electron transfer from Pheo − with a time constant of about 350 ± 100 ps.