The reduction state of the Q‐pool regulates the electron flux through the branched respiratory network of Paracoccus denitrificans

Abstract

In this work we demonstrate how the reduction state of the Q-pool determines the distribution of electron flow over the two quinol-oxidising branches in Paracoccus denitrificans: one to quinol oxidase, the other via the cytochrome bc 1 complex to the cytochrome c oxidases. The dependence of the electron-flow rate to oxygen on the fraction of quinol in the Q-pool was determined in membrane fractions and in intact cells of the wild-type strain, a bc 1 -negative mutant and a quinol oxidase-negative mutant. Membrane fractions of the bc 1 -negative mutant consumed oxygen at significant rates only at much higher extents of Q reduction than did the wild-type strain or the quinol oxidase-negative mutant. In the membrane fractions, dependence on the Q redox state was exceptionally strong corresponding to elasticity coefficients close to 2 or higher. In intact cells, the dependence was weaker. In uncoupled cells the dependence of the oxygen-consumption rates on the fractions of quinol in the Q-pool in the wildtype strain and in the two mutants came closer to that found for the membrane fractions. We also determined the dependence for membrane fractions of the wild-type in the absence and presence of antimycin A, an inhibitor of the bc 1 complex. The dependence in the presence of antimycin A resembled that of the bc 1 -negative mutant. These results indicate that electron-flow distribution between the two quinol-oxidising branches in P. denitrificans is not only determined by regulated gene expression but also, and to a larger extent, by the reduction state of the Q-pool.

Cytochromes c 550 , c 552 , and c 1 in the Electron Transport Network of Paracoccus denitrificans : Redundant or Subtly Different in Function?

“…However, it is not possible to deduce from these numbers the relative electron fluxes through the parallel electron transfer pathways in the wild-type cells. This is because every mutation in these mutants gives rise to changes in the kinetics of the remaining electron transfer reactions as a consequence of (i) changes in the expression levels of the respiratory components (28) and (ii) changes in the reduction levels of them (27).…”

“…The third type of oxidase is a ba 3 -type quinol oxidase, which is the counterpart of the bo 3 -type quinol oxidase found in Escherichia coli (8,35). The ba 3 -type oxidase receives electrons from ubiquinol, is expressed and increasingly active under conditions that give rise to high reduction levels of the Q-pool, and apparently serves to prevent that by rapidly transferring electrons from ubiquinol to oxygen (27). P. denitrificans is also able to synthesize four types of Noxide oxidoreductase, which catalyze the sequential reduction of nitrate to dinitrogen gas via the intermediates nitrite, nitric oxide, and nitrous oxide.…”

Regulation of the aerobic respiratory chain in the facultatively aerobic and hyperthermophilic archaeon Pyrobaculum oguniense

“…In these studies, additional functions of terminal oxidases were observed in a few species of bacteria. For example, Paracoccus denitrificans has three terminal oxidases: cbb 3 -type cytochrome c oxidase (FixN type) is expressed at a low oxygen concentration, aa 3 -type cytochrome c oxidase (SoxM type) is expressed at atmospheric oxygen concentration, and the pathway to ba 3 -type quinol oxidase (SoxM type) becomes active when the reduction state of the Q-pool increases (Otten et al, 1999(Otten et al, , 2001). E. coli has a bo 3 -type quinol oxidase (SoxM-type) that is utilized for atmospheric oxygen concentrations and a bd-type quinol oxidase (alternative oxidase) that is utilized for limited oxygen tension (Kita et al, 1984a, b).…”

Identification of ccdA in Paracoccus pantotrophus GB17: Disruption of ccdA Causes Complete Deficiency in c -Type Cytochromes

“…P. pantotrophus (formerly Paracoccus denitrificans and Thiosphaera pantotropha [31,38,41]) has a branched electron transfer network. The electron flux is regulated by the reduction of the Q pool (33). While the transfer of electrons by the terminal cytochrome oxidases aa 3 and cbb 3 results in a translocation of six protons (6H ϩ /2e Ϫ ) (36,54), the reduction of a terminal electron acceptor by the quinol oxidase o results in a translocation of only four protons (4H ϩ /2e Ϫ ) (39).…”