Analysis of the electron transfer from Pheo− to QA in PS II membrane fragments from spinach by time resolved 325 nm absorption changes in the picosecond domain

FEBS Letters

Bernarding, J.¹  Eckert, H.-J.²  Renger, G.²  Wiese, N.¹  Eichler, H.-J.¹ 

[1] Optisches Institut der Technischen Universität, Berlin, Germany;Max-Volmer-Institut für Biophysikalische und Physikalische Chemie, Berlin, Germany

关键词: Photosystem II;    Electron transfer;    QA-reduction kinetics;    Pheophytin;    Charge separation;    ΔA 325;    absorption changes at 325 nm;    Car;    carotenoid;    Chl;    chlorophyll;    I;    intermediary electron acceptor(s);    Pheo;    pheophytin;    PS II;    photosystem II;    QA;    primary plastoquinone acceptor;    Z and Zox;    reduced and oxidized form of the electron donor to P680;   

DOI  :  10.1016/0014-5793(88)80358-2

学科分类：生物化学/生物物理

来源: John Wiley & Sons Ltd.

【 摘 要 】

Absorption changes at 325 nm (ΔA 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 × 10¹⁴ photons/cm² per pulse) subtraction of the absorption changes in closed RCs (ΔA ^closed ₃₂₅) from those in open RCs (ΔA ^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.

【 授权许可】

Unknown