The H⁺/ATP coupling ratio of the ATP synthase from thiol‐modulated chloroplasts and two cyanobacterial strains is four

Abstract

In this paper the authors emphasise that the proton translocating ATP synthase from thiol-modulated chloroplasts and two cyanobaeterial strains has a coupling ratio of 4 protons per ATP synthesised or hydrolysed. This ratio is determined by several thermodynamic studies at equilibrium between phosphate potential (AGp) and proton gradient (zl/iu+), and is confirmed by measurement of proton flux during ATP hydrolysis. Ratios lower than 4 H+IATP that have been published in the past have predominantly been determined with the oxidised chloroplast enzyme. Errors in these measurements will be discussed.

Rotation of the c subunit oligomer in fully functional F1Fo ATP synthase

“…Thus, in ATP synthesis, a proton gradient would drive the rotation of the c subunit ring (clockwise when viewed from a periplasmic side), which would allow the ␥ subunit to interact sequentially with the three ␣␤ pairs in a way that favors synthesis of ATP in the catalytic sites, each from already bound ADP and P i . In this mechanism, three molecules of ATP would be synthesized in one full turn of the rotor (requiring translocation of 12 protons), which gives an ATP͞proton ratio of 1:4, close to that observed experimentally (22)(23)(24). In the reverse direction (ATP hydrolysis), it can be imagined that rotation of the ␥--c rotor (counterclockwise) brings c subunits that had been protonated from a cytoplasmic side (at Asp-61 in E. coli numbering system) into contact with the a subunit for deprotonation and subsequent release of the proton on the opposite side of the membrane.…”

Kinetic modelling of the proton translocating CF0CF1‐ATP synthase from spinach

“…The calibration with respect to pHi~ was realized by a series of different equilibrium states at the ATP synthase where the phosphate potential is balanced by the transmembrane potential of H + as described in detail elsewhere [15,16]. The H+/ATP coupling ratio of 4 used during this procedure has been confirmed recently [17]. The resulting calibration curve is presented in Fig.…”

“…The detailed reaction pattern used here is presented in Fig. 5 and may be described as follows: (1 [15,17]. (6) The events attributed to the membrane-spanning F0 domain are described as a series of four conformational changes A0 ~ A1 ~ A2 ~ A3 ~ A4, each step being driven by the translocation of one proton across F0 from the inside to the out-…”

Estimating the rotation rate in the vacuolar proton-ATPase in native yeast vacuolar membranes

“…This stoichiomerty is different form that of F-ATPase, in which there are ~12 c subunits, which have only 2 trans-membrane helices, each with a unique glutamic acid. So in FATPase a synthesis of one ATP also drives 120 degrees rotation, which, however, requires a movement of 4 subunits c, hence 4 protons (Van Walraven et al 1996;Panke and Rumberg 1997;Stock et al 1999;Ferguson 2000;Seelert et al 2000;Stahlberg et al 2001). In the case of F-ATPase rotation and ATP synthesis is driven by trans-membrane delta pH, but it should be noted that both enzymes can work in both directions depending on the conditions Itoh et al 2004;Rondelez et al 2005;Feniouk et al 2007;Nakano et al 2008).…”