Phase II of carotenoid bandshift is mainly due to the electrogenic protonation of the secondary quinone acceptor

• Published in: FEBS letters 1988-06, Vol.233 (2), p.315-318
• Main Authors: Drachev, Lel A., Mamedov, Mahir D., Mulkidjanian, Armen Ya, Semenov, Alexey Yu, Shinkarev, Vladimir P., Verkhovsky, Mikhail I.
• Format: Article
• Language: English
• Subjects: 4-morpholineethanesulphonic acid; Biological and medical sciences; Carotenoid; Cell structures and functions; Chloroplast, photosynthetic membrane and photosynthesis; Electrochromic absorbance change; Electron transfer; Fundamental and applied biological sciences. Psychology; Mes; Molecular and cellular biology; N,N,N′,N′-tetramethyl- p-phenylenediamine; P870; primary and secondary quinone acceptors of RC; Q AQ B; QAQB; Reaction center; reaction center bacteriochlorophyll dimer; Rhodobacter sphaeroides; TMPD; transmembrane electric potential difference
• ISSN: 0014-5793; 1873-3468
• DOI: 10.1016/0014-5793(88)80450-2

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 − AQ − B+2H + → Q AQ BH 2, but not solely by the oxidation of cytochrome c 2, as proposed earlier [(1973) Biochim. Biophys. Acta 325, 102–113].