title: Heterogeneity of photosynthetic membranes from Rhodobacter capsulatus: size dispersion and ATP synthase distribution.
abstract: The density distribution of photosynthetic membrane vesicles (chromatophores) from Rhodobacter capsulatus has been studied by isopicnic centrifugation. The average vesicle diameters, examined by electron microscopy, varied between 61 and 72 nm in different density fractions (70 nm in unfractionated chromatophores). The ATP synthase catalytic activities showed maxima displaced toward the higher density fractions relative to bacteriochlorophyll, resulting in higher specific activities in those fractions (about threefold). The amount of ATP synthase, measured by quantitative Western blotting, paralleled the catalytic activities. The average number of ATP synthases per chromatophore, evaluated on the basis of the Western blotting data and of vesicle density analysis, ranged between 8 and 13 (10 in unfractionated chromatophores). Poisson distribution analysis indicated that the probability of chromatophores devoid of ATP synthase was negligible. The effects of ATP synthase inhibition by efrapeptin on the time course of the transmembrane electric potential (evaluated as carotenoid electrochromic response) and on ATP synthesis were studied comparatively. The ATP produced after a flash and the total charge associated with the proton flow coupled to ATP synthesis were more resistant to efrapeptin than the initial value of the phosphorylating currents, indicating that several ATP synthases are fed by protons from the same vesicle.
authors.affiliation: Department of Biology, University of Bologna, Laboratory of Biochemistry and Biophysics, Via Irnerio, 42 I-40126, Bologna, Italy.
authors.forename: Francesca
authors.initials: F
authors.lastname: Gubellini
authors.forename: Francesco
authors.initials: F
authors.lastname: Francia
authors.forename: Paola
authors.initials: P
authors.lastname: Turina
authors.forename: Daniel
authors.initials: D
authors.lastname: Lévy
authors.forename: Giovanni
authors.initials: G
authors.lastname: Venturoli
authors.forename: B Andrea
authors.initials: BA
authors.lastname: Melandri
mesh_terms: D000255:Adenosine Triphosphate / Q000737:chemistry / Q000378:metabolism; D020130:Bacterial Chromatophores / Q000737:chemistry / Q000201:enzymology* / Q000648:ultrastructure; D025243:Bacterial Proton-Translocating ATPases / Q000037:antagonists & inhibitors / Q000737:chemistry / Q000378:metabolism*; D015153:Blotting, Western; D002338:Carotenoids / Q000737:chemistry / Q000378:metabolism; D002499:Centrifugation, Density Gradient; D006868:Hydrolysis / Q000187:drug effects; D007700:Kinetics; D008027:Light; D008854:Microscopy, Electron; D010455:Peptides / Q000494:pharmacology; D010766:Phosphorylation / Q000187:drug effects; D016354:Rhodobacter capsulatus / Q000737:chemistry / Q000201:enzymology* / Q000648:ultrastructure; D012542:Scattering, Radiation; D013056:Spectrophotometry, Ultraviolet; D013395:Sucrose / Q000737:chemistry
chemical_list: D010455:Peptides; D002338:Carotenoids; C012953:efrapeptin; D013395:Sucrose; D000255:Adenosine Triphosphate; D025243:Bacterial Proton-Translocating ATPases