Cationic antiseptics disrupt the functioning of the electron-transport chain at the acceptor site in the photosynthetic reaction centres of the purple bacterium Cereibacter sphaeroides

Electrometric technique revealed that the cationic antiseptic octenidine reduces the 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 are observed. The addition of cationic antiseptics resulted in the appearance of absorption changes in this region with the formation time of about 100-200 ms and a decay time of about 3 s. In the series: picloxidine – chlorhexidine – octenidine – miramistin, the latter was the most effective. The maximum amplitude of such changes was observed in the absorption region of the semiquinone radical around 460 nm. When blocking the electron transfer from Q⁻_A to Q_B by o-phenanthroline, the effect disappeared. It is suggested that cationic antiseptics stimulate protonation of Q⁻_B with the formation of a neutral Q⁻_BH⁺ complex.