title: Thermodynamics of proton transport coupled ATP synthesis.
abstract: The thermodynamic H(+)/ATP ratio of the H(+)-ATP synthase from chloroplasts was measured in proteoliposomes after energization of the membrane by an acid base transition (Turina et al. 2003 [13], 418-422). The method is discussed, and all published data obtained with this system are combined and analyzed as a single dataset. This meta-analysis led to the following results. 1) At equilibrium, the transmembrane ΔpH is energetically equivalent to the transmembrane electric potential difference. 2) The standard free energy for ATP synthesis (reference reaction) is ΔG°(ref)=33.8±1.3kJ/mol. 3) The thermodynamic H(+)/ATP ratio, as obtained from the shift of the ATP synthesis equilibrium induced by changing the transmembrane ΔpH (varying either pH(in) or pH(out)) is 4.0±0.1. The structural H(+)/ATP ratio, calculated from the ratio of proton binding sites on the c-subunit-ring in F(0) to the catalytic nucleotide binding sites on the β-subunits in F(1), is c/β=14/3=4.7. We infer that the energy of 0.7 protons per ATP that flow through the enzyme, but do not contribute to shifting the ATP/(ADP·Pi) ratio, is used for additional processes within the enzyme, such as activation, and/or energy dissipation, due e.g. to internal uncoupling. The ratio between the thermodynamic and the structural H(+)/ATP values is 0.85, and we conclude that this value represents the efficiency of the chemiosmotic energy conversion within the chloroplast H(+)-ATP synthase.
authors.affiliation: Department of Biology, BiGeA, University of Bologna, Via Irnerio 42, I-40126 Bologna, Italy.
authors.forename: Paola
authors.initials: P
authors.lastname: Turina
authors.affiliation: Biomedicine Discovery Institute, Monash University, 1 Wellington Rd., Clayton, Vic 3800, Australia.
authors.forename: Jan
authors.initials: J
authors.lastname: Petersen
authors.affiliation: Institut für Physikalische Chemie, University of Freiburg, Albertstr, 23a, D-79104 Freiburg, Germany. Electronic address: peter.graeber@physchem.uni-freiburg.de.
authors.forename: Peter
authors.initials: P
authors.lastname: Gräber
mesh_terms: D000255:Adenosine Triphosphate / Q000378:metabolism*; D000465:Algorithms; D001692:Biological Transport; D029968:Escherichia coli Proteins / Q000378:metabolism; D006863:Hydrogen-Ion Concentration; D007700:Kinetics; D008081:Liposomes / Q000378:metabolism; D010940:Plant Proteins / Q000378:metabolism; D006180:Proton-Translocating ATPases / Q000378:metabolism*; D011522:Protons; D029701:Saccharomyces cerevisiae Proteins / Q000378:metabolism; D013816:Thermodynamics
chemical_list: D029968:Escherichia coli Proteins; D008081:Liposomes; D010940:Plant Proteins; D011522:Protons; D029701:Saccharomyces cerevisiae Proteins; D000255:Adenosine Triphosphate; D006180:Proton-Translocating ATPases
keywords: Chemiosmosis; Efficiency of molecular motors; Equivalence of ΔpH and Δφ; F(0)F(1) ATP synthase; Proteoliposomes; Transmembrane electric potential