Effect of cationic antiseptics on the vectorial electron and proton transfer in chromatophores of photosynthetic bacteria.

The effect of the cationic antiseptics octenidine and miramistin on electron transfer reactions in photosynthetic bacterial chromatophores of Cereibacter sphaeroides has been studied using direct electrometric and flash photolysis techniques. When the ubiquinone pool and cytochrome bc₁ complex were oxidized, the addition of octеnidine at a concentration of 100 µM completely inhibited the generation of transmembrane electric potential difference (Δψ) caused by protonation of the doubly reduced secondary quinone acceptor Q_B in the reaction center and, accordingly, vectorial charge transfer within the bc₁ complex in response to a second laser flash. The lack of an effect of octenidine and miramistin on the rapid rise of Δψ (τ < 0.1 µs) due to charge separation between the primary electron donor P₈₇₀ and the primary quinone acceptor Q_A was accompanied by an acceleration of Δψ decay kinetics over a period of ~ 10 ms in the presence of the former. The effect of miramistin was less pronounced. Overall, the data obtained by the two methods are qualitatively similar. The different effects of octanidine and miramistin are undoubtedly due to their structural features and may be related to their disordering influences on both the Q_B-binding site of the reaction center and the structure of the bilayer phospholipid membrane of chromatophores. These results are also important for understanding the molecular mechanisms of action of cationic antiseptics on both charge transfer reactions and thylakoid membrane integrity in oxygenic photosynthetic organisms.