Inhibitory Effect of N,N'-Dicyclohexylcarbodiimide on Reduction of Cytochrome b560 and Stoichiometry of the Reduction in Chromatium Chromatophores

N,N'-Dicyclohexylcarbodiimide (DCCD) inhibited the flash-inducedreduction of cytochrome b₅₆₀, by blocking the electron flowbetween the secondary electron acceptor and cytochrome b₅₆₀presumably in the vicinity of the ubiquinone pool. The stoichiometryof the reduced cytochrome b₅₆₀ per reaction center bacteriochlorophylldimer was 0.77?0.12 throughout the redox potential range of150 to 390 mV at pH 7.0. The high stoichiometry suggested thatmost of the electrons ejected from the reaction center reducedcytochrome b₅₆₀. (Received January 19, 1982; Accepted March 15, 1982)