Transduction of light dependent signals to redox sensitive kinases in photosynthetic membranes modulates energy transfer to the photochemical reaction centres and regulates biogenesis, stability and turnover of thylakoid protein complexes. The occupancy of the quinol-oxidation site of the cytochrome bf complex by plastoquinol and the redox state of protein thiol groups act as elements of the si...

Quinol oxidation in the catalytic quinol oxidation site (Q(o) site) of cytochrome (cyt) bc(1) complexes is the key step of the Q cycle mechanism, which laid the ground for Mitchell's chemiosmotic theory of energy conversion. Bifurcated electron transfer upon quinol oxidation enables proton uptake and release on opposite membrane sides, thus generating a proton gradient that fuels ATP synthesis ...

The suitability of ubiquinol(1) and duroquinol as pulse reductants for initiating respirationdriven proton translocation by aerobic ox heart mitochondria was investigated. At 25 degrees C the V(max.) for oxidation was close to 280nmol of quinol oxidized/min per mg of protein, and the K(m) values were 8mum for ubiquinol(1) and 28mum for duroquinol. Pulses of ubiquinol(1) and duroquinol were rapi...

Energy transduction in the cytochrome bc(1) complex is achieved by catalyzing opposite oxido-reduction reactions at two different quinone binding sites. We have determined the pre-steady state kinetics of cytochrome b and c(1) reduction at varying quinol/quinone ratios in the isolated yeast bc(1) complex to investigate the mechanisms that minimize inhibition of quinol oxidation at center P by r...

Quinol oxidation by the bc(1) complex of Rhodobacter sphaeroides occurs from an enzyme-substrate complex formed between quinol bound at the Q(o) site and the iron-sulfur protein (ISP) docked at an interface on cytochrome b. From the structure of the stigmatellin-containing mitochondrial complex, we suggest that hydrogen bonds to the two quinol hydroxyl groups, from Glu-272 of cytochrome b and H...

We have investigated the mechanism responsible for half-of-the-sites activity in the dimeric cytochrome bc(1) complex from Paracoccus denitrificans by characterizing the kinetics of inhibitor binding to the ubiquinol oxidation site at center P. Both myxothiazol and stigmatellin induced a 2-3 nm shift of the visible absorbance spectrum of the b(L) heme. The shift generated by myxothiazol was sym...

It was shown by Cranes that plastoquinone is localized in the chloroplasts of higher plants, and there is now a good deal of evidence which suggests that it bctions as an oxidation-reduction carrier in the photosynthetic electron transport system. Bishop’ showed that when lyophilized chloroplasts were extracted with organic solvents they lost their Hill-reaction activity, but that this could be...

Oxidation of membrane-bound quinol molecules is a central step in the respiratory electron transport chains used by biological cells to generate ATP by oxidative phosphorylation. A novel family of cytochrome c quinol dehydrogenases that play an important role in bacterial respiratory chains was recognised in recent years. Here, we describe the first structure of a cytochrome from this family, N...