title: Kinetics of the quinone binding reaction at the QB site of reaction centers from the purple bacteria Rhodobacter sphaeroides reconstituted in liposomes.
abstract: 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.
authors: CNR, Istituto per i Processi Chimico-Fisici - Sezione di Bari Dipartimento di Chimica, Universitá di Bari, Italy.
authors: Francesco
authors: F
authors: Milano
authors: Angela
authors: A
authors: Agostiano
authors: Fabio
authors: F
authors: Mavelli
authors: Massimo
authors: M
authors: Trotta
mesh_terms: 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
chemical_list: D008081:Liposomes; D008823:Micelles; D045322:Photosynthetic Reaction Center Complex Proteins; D021122:Protein Subunits; D011809:Quinones