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Phase II of carotenoid bandshift is mainly due to the electrogenic protonation of the secondary quinone acceptor
Author(s) -
Drachev Lel A.,
Mamedov Mahir D.,
Mulkidjanian Armen Ya.,
Semenov Alexey Yu.,
Shinkarev Vladimir P.,
Verkhovsky Mikhail I.
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)80450-2
Subject(s) - chemistry , protonation , photochemistry , ferrocyanide , rhodobacter sphaeroides , phase (matter) , electron acceptor , electron transport chain , acceptor , kinetics , absorbance , electron transfer , biochemistry , photosynthesis , electrode , organic chemistry , chromatography , ion , physics , quantum mechanics , condensed matter physics
The flash‐induced kinetics of transmembrane electric potential (Δψ) generation with a rise‐time of 0.1–0.2 ms were investigated in Rhodobacter sphaeroides chromatophores by electrometry and by monitoring the electrochromic absorbance changes of carotenoids. An analysis of the results obtained electrometrically shows that this electrogenic phase is observed only after even‐numbered flashes. The sensitivity of this phase to o ‐phenanthroline, the flash‐number dependence of its amplitude and the decrease of its rise‐time with decreasing pH indicate that it is due to the dismutation of Q − A and Q − B and to subsequent protonation of a doubly reduced ubiquinone Q B molecule. The phase of the carotenoid bandshift with τ∼0.1 ms (the so‐called phase II) was shown to be sensitive to o ‐phenanthroline, with its rise‐time decreasing with decreasing pH. It is concluded that a considerable part of phase II of the electrochromic carotenoid changes with τ∼0.1 ms is caused by the electrogenic reaction Q − A Q − B +2H + → Q A Q B H 2 , but not solely by the oxidation of cytochrome c 2 , as proposed earlier [(1973) Biochim. Biophys. Acta 325, 102–113].