Ferricyanide-induced absorbance change of carotenoid in chromatophores ofRhodopseudomonas spheroidescorrelated to the oxidation of bacteriochlorophyll 885

摘要

Addition of high concentrations (e.g., 1–100 mM) of ferricyanide to a chromatophorc suspension ofRhodopseudomonas spheroidescaused a change in the absorption spectrum of carotenoid (spheroidene), which was completely reversed by adding reducing reagents such as ferrocyanide and ascorbate. The spectral change is represented by a shift in the absorption spectrum of carotenoid by 2 to 2.5 nm towards the longer wavelength side. The presence of piericidin A,o-phenanthroline or Cl-CCP in the reaction mixture did not affect the ferricyanide-induced absorbance change. Triton X-100 markedly suppressed the magnitude of the change. The addition of ferricyanide also caused simultaneous absorbance changes with maxima at 590 and 885 nm. These are ascribed to oxidation of the (bulk) bacteriochlorophyll, BChl 885. There was no absorption change at other peaks of bacteriochlorophyll in the infrared region (i.e., 800 and 855 nm). Therefore, the ferricyanide-induced absorbance change of carotenoid did not represent an oxidation-reduction reaction of carotenoid but was intimately correlated with oxidation of BChl 885 in the chromatophores, as judged from similarities observed with respect to the time course patterns, midpoint potential (545–555 mv) in the ferriferrocyanide reaction system, as well as behavior towards various reagents and inhibitors added. A similar change of carotenoid (i.e., 2–2.5 nm shift of absorption spectrum) was caused by addition of MgCl2to the chromatophores, but this did not induce any change in the absorption spectrum of bacteriochlorophyll. The nature of the spectral change of carotenoid in chromatophores is disc