Inhibitory effect of N,N'-dicyclohexylcarbodiimide (DCCD) on the electron transfer involving cytochrome b-c2 oxidoreductase in Rhodopseudomonas sphaeroides

N,N'-Dicyclohexylcarbodiimide (DCCD) inhibited dark re-reduction of cytochrome c2 and reduction of b-type cytochrome, both of which are closely associated with electron transfer involving a cytochrome b-c2 oxidoreductase, after a single-turnover flash excitation in the chromatophore membranes from a photosynthetic bacterium, Rhodopseudomonas sphaeroides. Rapid proton uptakes (HI+, HII+) and the formation of the membrane potential registered by carotenoid bandshift phase III were also inhibited by DCCD. The electron transfer was inhibited in the presence of either valinomycin or carbonylcyanide-m-chlorophenylhydrazone (CCCP). These results indicated that DCCD inhibited the electron transfer involving the cytochrome b-c2 oxidoreductase in the bacterium. The inhibition was irreversible. A hydrophilic carbodiimide, 1-ethyl-3-(3-dimethylaminopropyl)-carbodiimide (EDAC), did not affect the above-mentioned reactions. Thus, DCCD may interact with the hydrophobic region(s) in the chromatophore membranes from photosynthetic bacteria resulting in the inhibition(s) of the photosynthetic cyclic electron transfer.