Cationic Antiseptics Disrupt the Functioning of the Electron-Transport Chain at the Acceptor Side in the Photosynthetic Reaction Centres of the Purple Bacterium Cereibacter sphaeroides

Abstract

Using electrometric technique, the cationic antiseptic octenidine was revealed to reduce generation of transmembrane electrical potential difference in the chromatophores of photosynthetic bacterium Cereibacter sphaeroides. This is also confirmed by measurements of electrochromic shifts of carotenoid absorption bands in chromatophores. In reaction centers (RCs), isolated from chromatophores in the absence of external electron donors and acceptors, the rate of recombination between photooxidized bacteriochlorophyll P₈₇₀ and reduced secondary quinone acceptor Q_B, as measured by absorption changes in the near infrared region, was very weakly dependent on the presence of antiseptics, in contrast to the kinetics in the 400-600 nm spectral range, where absorption changes associated with the oxidation of P₈₇₀ and the formation of semiquinone radicals Q_A⁻ and Q_B⁻, as well as electrochromic shifts of the carotenoid and bacteriopheophytin RC absorption bands, were observed. The addition of cationic antiseptics modified the flash-induced absorbance changes in this region with the formation time of ~100-200 ms and a decay time of ~3 s. In the series: picloxydine – chlorhexidine – octenidine – miramistin, the last one was the most effective. The maximum amplitude of such changes was observed in the absorption region of the semiquinone radical around 460 nm. When electron transfer from Q_A⁻ to Q_B was blocked by o-phenanthroline, the effect disappeared. Cationic antiseptics are suggested to stimulate protonation of Q_B⁻ with the formation of a neutral Q_B⁻H⁺ complex.