title: Light induced transmembrane proton gradient in artificial lipid vesicles reconstituted with photosynthetic reaction centers.
abstract: Photosynthetic reaction center (RC) is the minimal nanoscopic photoconverter in the photosynthetic membrane that catalyzes the conversion of solar light to energy readily usable for the metabolism of the living organisms. After electronic excitation the energy of light is converted into chemical potential by the generation of a charge separated state accompanied by intraprotein and ultimately transmembrane proton movements. We designed a system which fulfills the minimum structural and functional requirements to investigate the physico/chemical conditions of the processes: RCs were reconstituted in closed lipid vesicles made of selected lipids entrapping a pH sensitive indicator, and electron donors (cytochrome c₂ and K₄[Fe(CN)₆]) and acceptors (decylubiquinone) were added to sustain the photocycle. Thanks to the low proton permeability of our preparations, we could show the formation of a transmembrane proton gradient under illumination and low buffering conditions directly by measuring proton-related signals simultaneously inside and outside the vesicles. The effect of selected ionophores such as gramicidin, nigericin and valinomycin was used to gain more information on the transmembrane proton gradient driven by the RC photochemistry.
authors.affiliation: Institute for Physical and Chemical Processes-IPCF, Bari Division, Italian National Research Council-CNR, Via Orabona 4, 70126 Bari, Italy.
authors.forename: Francesco
authors.initials: F
authors.lastname: Milano
authors.forename: Massimo
authors.initials: M
authors.lastname: Trotta
authors.forename: Márta
authors.initials: M
authors.lastname: Dorogi
authors.forename: Béla
authors.initials: B
authors.lastname: Fischer
authors.forename: Livia
authors.initials: L
authors.lastname: Giotta
authors.forename: Angela
authors.initials: A
authors.lastname: Agostiano
authors.forename: Péter
authors.initials: P
authors.lastname: Maróti
authors.forename: László
authors.initials: L
authors.lastname: Kálmán
authors.forename: László
authors.initials: L
authors.lastname: Nagy
mesh_terms: D018929:Cell Culture Techniques; D007476:Ionophores / Q000737:chemistry; D008027:Light; D008081:Liposomes / Q000737:chemistry*; D008856:Microscopy, Fluorescence; D045322:Photosynthetic Reaction Center Complex Proteins / Q000737:chemistry*; D011522:Protons; D013056:Spectrophotometry, Ultraviolet
chemical_list: D007476:Ionophores; D008081:Liposomes; D045322:Photosynthetic Reaction Center Complex Proteins; D011522:Protons