Abstract
A chlorosomes-less green filamentous bacterium Roseiflexus castenholzii has a similar photosynthetic reaction center (RC) to Chloroflexus aurantiacus. The pathway of photosynthetic electron transfer to RC in Cfx. aurantiacus has not been known, except for the participation of auracyanin as the electron donor to RC. Spectroscopic measurements in R. castenholzii are easier than in Cfx. aurantiacus due to the lack of chlorosomes.
In the membrane preparations of R. castenholzii, the photooxidized RC-bound cytochrome c was re-reduced after the flash activation, indicating electron donation from membrane-bound proteins. Since an auracyanin-like fraction prepared from the membrane reduced the RC-bound cytochrome c , this protein was suggested to be auracyanin. In the presence of 20μM of HQNO, the re-reduction of the RC-bound cytochrome c in the membrane was inhibited. This result suggests that a quinol-auracyanin oxidoreductase as well as auracyanin are working in the electron transfer pathway to RC in R. castenholzii.
