Flash-induced electron transport in b- and c-type cytochromes in Rhodospirillum rubrum. Evidence for a Q-cycle

Isolation of cytochrome bc 1 complexes from the photosynthetic bacteria Rhodopseudomonas viridis and Rhodospirillum rubrum

“…concentrations of antimycin A and myxothiazol, two specific inhibitors of electron transport through the cytochrome bca region of a number of organisms [18,10,9], including R. rubrum [37]. The Rps.…”

“…While R. rubrum was known to contain multiple b-cytochromes [13], at least two of which participate in light-dependent electron flow [37], and a Rieske protein [41 ], no evidence had been presented for the third component of a cytochrome bcl complex, cytochrome ca, in this bacterium [37]. The spectral evidence of Figure 2B and the presence of a 30 kDa, heme c-containing peptide in R. rubrum ( Figure 5B) membranes provide unequivocal evidence for the presence of cytochrome cl in R. rubrurn.…”

“…The observation that the isolated R. rubrum complex exhibits quinol: cytochrome c-oxidoreductase activity that is sensitive to the two highly specific inhibitors antimycin A and myxothiazol [37] (see Table 2) suggests that the basic characteristics of electron flow through the native complex have [192] survived the isolation procedure. The fact that the isolated R. rubrum cytochrome bcl complex apparently can form an electrostatic complex (see Figure 4B) with immobilized equine cytochrome c (a cytochrome with many structural similarities to the endogenous cytochrome c2 [27]) suggests the presence of a cytochrome c/c2 binding site in the R. rubrum complex.…”

“…Thus, the data of Figure 2B do not allow one to conclude that more than one b-type cytochrome is present in the R. rubrum complex. However, it is possible that the R. rubrum complex contains more than one species of b-cytochrome since R. rubrum chromatophore membranes are known to contain at least two different b-type cytochromes active in photosynthetic electron transport [37,13]. As cytochrome bcl complexes isolated from a variety of sources contain the Rieske iron-sulfur protein [18,10,17,9], the acid-labile sulfide and nonheme iron contents oftheRps, viriclis andR.…”

In bacteria which grow on simple reductants, generation of a proton gradient involves extracytoplasmic oxidation of substrate.

“…In the organisms examined, one or more of the reaction center subunits (H, M, or L) are exposed at the periplasmic surface of the membrane. During cyclic photophosphorylation soluble and membrane c-type cytochromes (or multiple membrane-associated c-type cytochromes) have been shown to reduce the reaction center (47,48,63,68,113,172,188,200,233,236). The soluble cytochrome (cytochrome c2) has been localized in the periplasm of Rhodopseudomonas sphaeroides and R. capsulata (187).…”