Premium
Temperature dependence of the electrogenic reaction in the Q B site of the Rhodobacter sphaeroides photosynthetic reaction center: the Q A − Q B →Q A Q B − transition
Author(s) -
Gopta O.A.,
Bloch D.A.,
Cherepanov D.A.,
Mulkidjanian A.Y.
Publication year - 1997
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/s0014-5793(97)00842-9
Subject(s) - rhodobacter sphaeroides , photosynthetic reaction centre , chemistry , crystallography , stereochemistry , hydrogen bond , kinetics , acceptor , electron transfer , photochemistry , molecule , photosynthesis , physics , biochemistry , organic chemistry , quantum mechanics , condensed matter physics
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 C 3 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 A Q B –H–Glu transition, whereas the slow one to the Q A − Q B :Glu − →Q A − Q B –H–Glu→Q A Q B − –H–Glu transition.