Temperature dependence of the electrogenic reaction in the QB site of the Rhodobacter sphaeroides photosynthetic reaction center: the QA −QB→QAQB − transition

FEBS Letters

Gopta, O.A.²  Mulkidjanian, A.Y.²  Bloch, D.A.²  Cherepanov, D.A.¹ 

[1] A.N. Frumkin Institute of Electrochemistry, Russian Academy of Sciences, Leninskii prosp. 31, 117071 Moscow, Russia;A.N. Belozersky Institute of Physico-Chemical Biology, Moscow State University, 119899 Moscow, Russia

关键词: Purple photosynthetic bacterium;    Photosynthetic reaction center;    Ubiquinone;    Electron transfer;    Proton transfer;    Electrogenesis;    (Rhodobacter sphaeroides);   

DOI  :  10.1016/S0014-5793(97)00842-9

学科分类：生物化学/生物物理

来源: John Wiley & Sons Ltd.

【 摘 要 】

The temperature dependencies for the kinetics and relative amplitudes of electrogenic reaction(s) coupled with the first reduction of the secondary quinone acceptor Q_B were measured with dark-adapted chromatophores of Rhodobacter sphaeroides. The kinetics, while acceptably fitted by a single exponent at room temperature, clearly split into two components below 15°C (rise times, 25 μs and 300 μs at pH 7.0 and 10°C) with the slow phase ousting the fast one at pH>9.0. The activation energies of the fast and slow phases were estimated at pH 7.0 as <10 kJ/mol and 60–70 kJ/mol, respectively. To explain the kinetic heterogeneity of the Q_B→Q_B ⁻ transition, we suggest two possible conformations for the neutral oxidized ubiquinone at the Q_B site: one with a hydrogen bond between the side chain carboxyl of Glu-L212 and the methoxy oxygen at C₃ of the Q_B ring (Q_B−H-Glu centers) and the other one, without this bond (Q_B:Glu⁻ centers). The fast phase is attributed to Q_A ⁻Q_B–H–Glu→Q_AQ_B–H–Glu transition, whereas the slow one to the Q_A ⁻Q_B:Glu⁻→Q_A ⁻Q_B–H–Glu→Q_AQ_B ⁻–H–Glu transition.

【 授权许可】

Unknown