title: Unreliability of carotenoid electrochromism for the measure of electrical potential differences induced by ATP hydrolysis in bacterial chromatophores.
abstract: ATP hydrolysis induces the activation of the proton ATPase in chromatophores of Rhodobacter capsulatus supplemented with nigericine and 50 mM K+ (i.e. when delta pH < 0.2 units). The value of transmembrane electric potential (delta phi) driving this activation was measured using three different approaches: carotenoid electrochromism, uptake of SCN- and responses of the dye oxonol VI. The value of delta phi calculated from the SCN- uptake, on the basis of an internal volume determined experimentally, was about 140 mV, while that indicated by the electrochromic signal ranged between 35 and 70 mV. Only the value indicated by SCN- distribution is consistent with the energetic requirement for the activation of H(+)-ATPase.
authors.affiliation: Department of Biology, University of Bologna, Italy.
authors.forename: M
authors.initials: M
authors.lastname: Crimi
authors.forename: V
authors.initials: V
authors.lastname: Fregni
authors.forename: A
authors.initials: A
authors.lastname: Altimari
authors.forename: B A
authors.initials: BA
authors.lastname: Melandri
mesh_terms: D000255:Adenosine Triphosphate / Q000378:metabolism*; D020130:Bacterial Chromatophores / Q000378:metabolism; D001692:Biological Transport; D002338:Carotenoids / Q000378:metabolism*; D004789:Enzyme Activation; D006868:Hydrolysis; D008027:Light; D008564:Membrane Potentials; D006180:Proton-Translocating ATPases / Q000378:metabolism*; D016354:Rhodobacter capsulatus / Q000378:metabolism*; D013861:Thiocyanates / Q000378:metabolism
chemical_list: D013861:Thiocyanates; D002338:Carotenoids; D000255:Adenosine Triphosphate; D006180:Proton-Translocating ATPases; C031760:thiocyanate