title: Estimating the rotation rate in the vacuolar proton-ATPase in native yeast vacuolar membranes.
abstract: The rate of rotation of the rotor in the yeast vacuolar proton-ATPase (V-ATPase), relative to the stator or steady parts of the enzyme, is estimated in native vacuolar membrane vesicles from Saccharomyces cerevisiae under standardised conditions. Membrane vesicles are formed spontaneously after exposing purified yeast vacuoles to osmotic shock. The fraction of total ATPase activity originating from the V-ATPase is determined by using the potent and specific inhibitor of the enzyme, concanamycin A. Inorganic phosphate liberated from ATP in the vacuolar membrane vesicle system, during ten min of ATPase activity at 20 °C, is assayed spectrophotometrically for different concanamycin A concentrations. A fit of the quadratic binding equation, assuming a single concanamycin A binding site on a monomeric V-ATPase (our data are incompatible with models assuming multiple binding sites), to the inhibitor titration curve determines the concentration of the enzyme. Combining this with the known ATP/rotation stoichiometry of the V-ATPase and the assayed concentration of inorganic phosphate liberated by the V-ATPase, leads to an average rate of ~10 Hz for full 360° rotation (and a range of 6-32 Hz, considering the ± standard deviation of the enzyme concentration), which, from the time-dependence of the activity, extrapolates to ~14 Hz (8-48 Hz) at the beginning of the reaction. These are lower-limit estimates. To our knowledge, this is the first report of the rotation rate in a V-ATPase that is not subjected to genetic or chemical modification and is not fixed to a solid support; instead it is functioning in its native membrane environment.
authors.affiliation: Institute of Biophysics, Biological Research Centre, Temesvári krt. 62, 6726, Szeged, Hungary.
authors.forename: Csilla
authors.initials: C
authors.lastname: Ferencz
authors.forename: Pál
authors.initials: P
authors.lastname: Petrovszki
authors.forename: Zoltán
authors.initials: Z
authors.lastname: Kóta
authors.forename: Elfrieda
authors.initials: E
authors.lastname: Fodor-Ayaydin
authors.forename: Lajos
authors.initials: L
authors.lastname: Haracska
authors.forename: Attila
authors.initials: A
authors.lastname: Bóta
authors.forename: Zoltán
authors.initials: Z
authors.lastname: Varga
authors.forename: András
authors.initials: A
authors.lastname: Dér
authors.forename: Derek
authors.initials: D
authors.lastname: Marsh
authors.forename: Tibor
authors.initials: T
authors.lastname: Páli
mesh_terms: D055162:Biocatalysis; D007425:Intracellular Membranes / Q000201:enzymology*; D018942:Macrolides / Q000494:pharmacology; D008958:Models, Molecular; D010710:Phosphates / Q000378:metabolism; D017434:Protein Structure, Tertiary; D012399:Rotation; D012441:Saccharomyces cerevisiae / Q000166:cytology* / Q000201:enzymology*; D025262:Vacuolar Proton-Translocating ATPases / Q000037:antagonists & inhibitors / Q000737:chemistry* / Q000378:metabolism*; D014617:Vacuoles / Q000201:enzymology*
chemical_list: D018942:Macrolides; D010710:Phosphates; C036978:concanamycin A; D025262:Vacuolar Proton-Translocating ATPases