Evidence for cytochrome bc1 complex involvement in nitrite reduction in a photodenitrifier, Rhodopseudomonas sphaeroides forma sp. denitrificans

AbstractThe cytochrome bc1 complex which has a quinol : cytochrome c2 oxidoreductase activity was isolated from a photodenitrifier, Rhodopseudomonas sphaeroides forma sp. denitrificans. When duroquinol (tetramethyl-p-benzoquinol) was used as the electron donor, maximum nitrite reduction activity was obtained in an anaerobic mixture containing the isolated cytochrome bc1 complex, nitrite reductase and cytochrome c2 Nitrite reduction in chromatophore membranes, as well as in the reconstituted system, was inhibited in the presence of antimycin A. No nitrite reduction occurred in the absence of cytochrome c2. These results indicated that the cytochrome bc1 complex involved in photosynthetic electron transfer also donates reducing equivalents to the dissimilatory nitrite reductase via cytochrome c2 in this photodenitrifier