| Abstrakt: |
We studied the photosynthetic electron transfer system of membrane-bound and soluble cytochrome c in Chlorobium tepidum, a thermophilic green sulfur bacterium, using whole cells and membrane preparations. Sulfide and thiosulfate, physiological electron donors, enhanced flash-induced photo-oxidation of c-type cytochromes in whole cells. In membranes, c-553 cytochromes with two (or three) heme groups served as immediate electron donors for photo-oxidized bacteriochlorophyll (P840) in the reaction center, and appeared to be closely associated with the reaction center complex. The membrane-bound cytochrome c-553 had an E-value of 180 mV. When isolated soluble cytochrome c-553, which has an apparent molecular weight of 10 kDa and seems to correspond to the cytochrome c-555 in Chlorobium limicola and Chlorobium vibrioforme, was added to a membrane suspension, rapid photo-oxidation of both soluble and membrane-bound cytochromes c-553 was observed. The oxidation of soluble cytochrome c-553 was inhibited by high salt concentrations. In whole cells, photo-oxidation was observed in the absence of exogenous electron donors and re-reduction was inhibited by stigmatellin, an inhibitor of the cytochrome bc complex. These results suggest that the role of membrane-bound and soluble cytochrome c in C. tepidum is similar to the role of cytochrome c in the photosynthetic electron transfer system of purple bacteria. [ABSTRACT FROM AUTHOR] |
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