Electrogenic proton transfer in Rhodobacter sphaeroides reaction centers: effect of coenzyme Q(10) substitution by decylubiquinone in the Q(B) binding site

electrometric technique was used to investigate the effect of coenzyme Q(10 ) (UQ), substitution by decylubiquinone (dQ) at the Q(B) binding site of re action centers (UQ-RC and dQ-RC, respectively) on the electrogenic proton t ransfer kinetics upon Qs reduction in Rhodobacter sphaeroides chromatophore s, Unlike dQ-RC, the kinetics of the second flash-induced proton uptake in UQ-RC clearly deviated from the mono=exponential one, The activation energy (about 30 kJ/mol) and the pH profile of the kinetics in dQ-RC were similar to those in UQ-RC, with the power lan approximation used in the latter cas e, The interpretation of the data presumed the quinone translocation betwee n the two binding positions within the QB site, It is proposed that the nat ive isoprenyl side chain tin contrast to decyl chain) favors the equilibriu m binding of neutral quinone at the redox-active 'proximal' position, but c auses a higher barrier for the hydroquinone movement from 'proximal' to 'di stal' position. (C) 2001 Published by Elsevier Science B.V. on behalf of th e Federation of European Biochemical Societies.