FEBS Letters | |
Temperature dependence of the electrogenic reaction in the QB site of the Rhodobacter sphaeroides photosynthetic reaction center: the QA −QB→QAQB − transition | |
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 QB 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 QB→QB − transition, we suggest two possible conformations for the neutral oxidized ubiquinone at the QB site: one with a hydrogen bond between the side chain carboxyl of Glu-L212 and the methoxy oxygen at C3 of the QB ring (QB−H-Glu centers) and the other one, without this bond (QB:Glu− centers). The fast phase is attributed to QA −QB–H–Glu→QAQB–H–Glu transition, whereas the slow one to the QA −QB:Glu−→QA −QB–H–Glu→QAQB −–H–Glu transition.
【 授权许可】
Unknown
【 预 览 】
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RO201912020304721ZK.pdf | 580KB | download |