Specific Inhibition of Electron Transfer for Nitrate Reduction by a Low Concentration of Cyanide in Rhodobacter sphaeroides f. s. denitrificans

The effects of cyanide on the electron flow in NO₃^– andNO₂^– reductions and photosynthetic electron transfer wereinvestigated with intact cells of a photodenitrifier, Rhodobactersphaeroides f. s. denitrificans. In the presence of 30 µMKCN, electron transfer for NO₃^– reduction was inhibitedby about 70% and the concomitant H translocation was completelyinhibited. However, neither NO₂^– reduction nor photosyntheticcyclic electron transfer was affected at 30 µM. Theseresults suggested that the electron transfer pathway to NO₃^–has, in addition to a b-type cytochrome and the nitratereductase,a component sensitive to a low concenration of cyanide whichis not involvedin the cytochrome bc₁ complex. (Received April 13, 1987; Accepted July 23, 1987)