Kinetics of the quinone binding reaction at the QB site of reaction centers from the purple bacteria Rhodobacter sphaeroides reconstituted in liposomes.
Transmembrane proton translocation in the photosynthetic membranes of the purple bacterium Rhodobacter sphaeroides is driven by light and performed by two transmembrane complexes; the photosynthetic reaction center and the ubiquinol-cytochrome c oxidoreductase complex, coupled by two mobile electron carriers; the cytochrome and the quinone. This paper focuses on the kinetics and thermodynamics of the interaction between the lipophylic electron carrier ubiquinone-10 and the photosynthetic enzyme reconstituted in liposomes. The collected data were simulated with an existing recognized kinetic scheme and the kinetic constants of the uptake (7.2 x 107 M(-1) x s(-1)) and release (40 s(-1)) processes of the ligand were inferred. The results obtained for the quinone release kinetic constant are comparable to the rate of the charge recombination reaction from the state D(+)QA(-). Values for the kinetic constants are discussed as part of the overall photocycle, suggesting that its bottleneck may not be the quinone uptake reaction in agreement with a previous report.
Milano
Francesco
F
CNR, Istituto per i Processi Chimico-Fisici - Sezione di Bari Dipartimento di Chimica, Universitá di Bari, Italy.
Agostiano
Angela
A
Mavelli
Fabio
F
Trotta
Massimo
M
D001665:Binding Sites; D007700:Kinetics; D008027:Light; D008081:Liposomes / Q000378:metabolism*; D008823:Micelles; D008954:Models, Biological; D008956:Models, Chemical; D045322:Photosynthetic Reaction Center Complex Proteins / Q000378:metabolism*; D021122:Protein Subunits / Q000378:metabolism; D011809:Quinones / Q000378:metabolism*; D012242:Rhodobacter sphaeroides / Q000378:metabolism*; D013816:Thermodynamics
D008081:Liposomes; D008823:Micelles; D045322:Photosynthetic Reaction Center Complex Proteins; D021122:Protein Subunits; D011809:Quinones