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

Abstract

Cytochrome bc 1 complexes have been isolated from wild type Rhodopseudomonas viridis and Rhodospirillum rubrum and purified by affinity chromatography on cytochrome c-Sepharose 4B. Both complexes are largely free of bacteriochlorophyll and carotenoids and contain cytochromes b and c 1 in a 2:1 molar ratio. For the Rps. viridis complex, evidence has been obtained for two spectrally distinct b-cytochromes. The R. rubrum complex contains a Rieske iron-sulfur protein (present in approximately 1:1 molar ratio to cytochrome c 1) and catalyzes an antimycin A- and myxothiazol-sensitive electron transfer from duroquinol to equine cytochrome c or R. rubrum cytochrome c 2. Although an attempt to prepare a cytochrome bc 1 complex from the gliding green bacterium Chloroflexus aurantiacus was not successful, membranes isolated from phototrophically grown Cfl. aurantiacus were shown to contain a Rieske iron-sulfur protein and protoheme (the prosthetic group of b-type cytochromes).

Electron transfer between primary and secondary donors in Rhodospirillum rubrum: evidence for a dimeric association of reaction centers

“…The comparison of these three difference spectra indicates that the ratio of cyt q to cyt c2 lies between 0.1 and 0.15. Another indication that cyt c2 is in large excess compared to cyt q comes from the observation that the absorption changes of the photooxidized cytochrome is centered at 550.5 nm, very close to the cyt c2 maximum while cyt q peaks at 553 nm (Wynn et al, 1986). This estimation of the amount of cyt h/q complex is in agreement with the one reported by Van der Wal and Van Grondelle (1983).…”

A Point Mutation in the Mitochondrial Cytochrome b Gene Obviates the Requirement for the Nuclear Encoded Core Protein 2 Subunit in the Cytochrome bc1 Complex in Saccharomyces cerevisiae

“…It is possible that the remaining part of core protein 2 in cor2-45 (about half of the wild-type protein) helps the assembly of or stabilize the bc 1 complex, which could explain the observed differences in terms of activity and growth rates of the corresponding strains. These unexpected results illustrate unequivocally that the core 2 subunit of the mitochondrial cytochrome bc 1 complex is not essential for the electron transfer and energy transducing functions of this respiratory enzyme, which is consistent with the finding that cytochrome bc 1 complexes from bacteria do not contain such proteins (3,4).…”

“…Much less is known about the subunits that do not carry redox prosthetic groups. These are often referred to as supernumerary subunits because they have no counterparts in bacteria such as Paracoccus denitrificans and Rhodospirillum rubrum, where the cytochrome bc 1 complex contains only cytochrome b, cytochrome c 1 , and the Rieske iron-sulfur protein (3,4). The bacterial and mitochondrial cytochrome bc 1 complexes exhibit essentially identical electron transfer and proton translocating activities, suggesting that the supernumerary polypeptides of the mitochondrial enzyme are not directly involved in the energy transducing mechanism (5).…”

Cytochrome bc1 complexes of microorganisms.

“…The photosynthetic purple sulfur bacterium Chromatium vinosum (46,57), the photosynthetic green sulfur bacterium Chlorobium limicola (84), and the photosynthetic gliding green bacterium Chloroflexus aurantiacus (177,188) exhibit EPR signals characteristic of the Rieske iron-sulfur protein.…”