The interaction between cytochrome c2 and the cytochrome bc1 complex in the photosynthetic purple bacteria Rhodobacter capsulatus and Rhodopseudomonas viridis

Abstract

The rates of electron transfer from a ubiquinol analogue to cytochrome c2 catalyzed by the cytochrome bc1 complexes of Rhodobacter capsulatus and Rhodopseudomonas viridis were measured as a function of ionic strength. The effects of ionic strength on the kinetic parameters for the reactions are consistent with a role for electrostatic complex formation between cytochrome c2 and the cytochrome bc1 complex in the electron-transfer pathways in both photosynthetic purple non-sulfur bacteria. Additional support for a docking model in which positively charged lysines on cytochrome c2 interact with negatively charged groups on the Rb. capsulatus cytochrome bc1 complex was obtained from kinetic experiments using Rb. capsulatus cytochrome c2 and equine cytochrome c in which specific lysine residues were altered by site-directed mutagenesis and chemical modification, respectively. Equine cytochrome c, which is a poor electron donor to the reaction center of Rps. viridis, is an effective electron acceptor for the Rps. viridis cytochrome bc1 complex. Chemical modification of lysine residues on Rps. viridis cytochrome c2 has a substantially greater effect on the reduction of the Rps. viridis reaction center by ferrocytochrome c2 than on the oxidation of the Rps. viridis cytochrome bc1 complex by ferricytochrome c2. These data suggest that the docking site for Rps. viridis cytochrome c2 on the Rps. viridis reaction center tetraheme subunit differs in structure from the docking site for the cytochrome on the Rps. viridis cytochrome bc1 complex to a significant extent. In this respect, Rps. viridis differs from photosynthetic purple non-sulfur bacteria in which the reaction center does not contain a tetraheme subunit, where the binding sites for cytochrome c2 on the reaction center and the cytochrome bc1 complex appear to be quite similar.

Demonstration of Short-lived Complexes of Cytochrome c with Cytochrome bc1 by EPR Spectroscopy

“…7, and well known from other studies (24, 57), the turnover rate of cytochrome bc 1 is greatly dependent on the ionic strength. This could be in part the result of the ionic strength influencing the binding of cytochrome c to cytochrome bc 1 , a process known to involve the electrostatic interactions (24–26, 56). …”

Electronic Connection Between the Quinone and CytochromecRedox Pools and Its Role in Regulation of Mitochondrial Electron Transport and Redox Signaling

“…Electrostatic forces are considered to be a dominant factor that contributes to binding of cytochrome c to cytochrome bc 1 , which is inferred from a significant salt dependence of electron transfer between these proteins (90,114,121,135,249). An importance of short-range hydrophobic interactions between surfaces of cytochrome c 1 subunit and cytochrome c was proposed on the basis of X-ray structures of cytochrome bc 1 co-crystallized with its redox partner (152,238).…”

Supramolecular organization of photosynthetic complexes in membranes of Roseiflexus castenholzii

“…The turnover rates of purple bacterial cyt bc 1 complexes, measured as rate constant k, range from 30 to 70 s -1 (Table S1). The turnover of the ACIII was in the middle of the rates measured for two purple bacterial cyt bc 1 complexes indicating that, even though the complexes are completely different, this side of the ETC turns over at nearly equal rates in FAPs and other bacterial systems (Guner et al 1993;Gao et al 2009). …”