Steady-state cyclic electron transfer through solubilized Rhodobacter sphaeroides reaction centres.
The mechanism, thermodynamics and kinetics of light-induced cyclic electron transfer have been studied in a model energy-transducing system consisting of solubilized Rhodobacter sphaeroides reaction center/light harvesting-1 complexes (so-called core complexes), horse heart cytochrome c and a ubiquinone-0/ubiquinol-0 pool. An analysis of the steady-state kinetics of cytochrome c reduction by ubiquinol-0, after a light-induced steady-state electron flow had been attained, showed that the rate of this reaction is primarily controlled by the one-electron oxidation of the ubiquinol-anion. Re-reduction of the light-oxidized reaction center primary donor by cytochrome c was measured at different reduction levels of the ubiquinone-0/ubiquinol-0 pool. These experiments involved single turnover flash excitation on top of background illumination that elicited steady-state cyclic electron transfer. At low reduction levels of the ubiquinone-0/ubiquinol-0 pool, the total cytochrome c concentration had a major control over the rate of reduction of the primary donor. This control was lost at higher reduction levels of the ubiquinone/ubiquinol-pool, and possible reasons for this behaviour are discussed.
van Rotterdam
B J
BJ
Swammerdam Institute for Life Sciences, University of Amsterdam, Biocentrum Amsterdam, The Netherlands. bartvr@dds.nl
Westerhoff
H V
HV
Visschers
R W
RW
Jones
M R
MR
Hellingwerf
K J
KJ
Crielaard
W
W
D000818:Animals; D001429:Bacteriochlorophylls / Q000737:chemistry / Q000378:metabolism; D003574:Cytochrome c Group / Q000737:chemistry* / Q000378:metabolism; D004579:Electron Transport; D007700:Kinetics; D045342:Light-Harvesting Protein Complexes; D009206:Myocardium / Q000201:enzymology; D045322:Photosynthetic Reaction Center Complex Proteins / Q000737:chemistry / Q000378:metabolism*; D011522:Protons; D012242:Rhodobacter sphaeroides / Q000737:chemistry / Q000201:enzymology*; D013816:Thermodynamics; D014451:Ubiquinone / Q000031:analogs & derivatives / Q000737:chemistry* / Q000378:metabolism
D001429:Bacteriochlorophylls; D003574:Cytochrome c Group; D045342:Light-Harvesting Protein Complexes; D045322:Photosynthetic Reaction Center Complex Proteins; D011522:Protons; D014451:Ubiquinone