The Molecular Mechanism of ATP Synthesis by F1F0-ATP Synthase: A Scrutiny of the Major Possibilities

Abstract

There is a complicated hypothesis which usually entails an element of mystery and several unnecessary assumptions. This is opposed by a more simple explanation which contains no unnecessary assumptions. The complicated one is always the popular one at first, but the simpler one, as a rule, eventually is found to be correct. This process frequently requires 10 to 20 years. The reason for this long time lag was explained by Max Planck. He remarked that "Scientists never change their minds, but eventually die." J.H. NorthropA critical goal of metabolism in living cells is the synthesis of adenosine triphosphate (ATP). ATP is synthesized by the enzyme F 1 F 0 -ATP synthase. This enzyme, the smallest-known molecular machine, couples proton translocation through its membrane-embedded, hydrophobic domain, F 0 , to the synthesis of ATP from adenosine diphosphate (ADP) and inorganic phosphate (P i ) in its soluble, hydrophilic headpiece, F 1 . Animals, plants and microorganisms all capture and utilize energy by this important chemical reaction. How does it occur?The binding change mechanism and the torsional mechanism of energy transduction and ATP synthesis are two mechanisms that have been proposed in the literature. According to the binding change mechanism (which considers reversible catalysis and site-site cooperativity), energy is required primarily for release of synthesized ATP, but not for its synthesis. On the other hand, according to the torsional mechanism (which considers an irreversible mode of catalysis and absence of cooperativity), all the elementary steps require energy, and the ionprotein interaction energy obtained from the ion gradients is used to synthesize ATP, for P i binding, and for straining the b-e bond in order to enable ADP to bind. The energy to release preformed ATP from the tight catalytic site (b DP ) is provided by the formation of the b-e ester linkage. First, the central features of these mechanisms are clearly delineated. Then, a critical scrutiny of these mechanisms is undertaken. The predictions of the torsional mechanism are listed. In particular, how the torsional mechanism deals with the specific difficulties associated with other mechanisms, and how it seeks to explain a wealth of structural, spectroscopic, and biochemical data is discussed in detail. Recent experimental data in support of the mechanism are presented. Finally, in view of the molecular machine nature of energy transduction, the indispensability of applying engineering tools at the molecular level is highlighted. This paves the way for the development of a new field: Molecular Physiological Engineering.

Energy Transfer from Adenosine Triphosphate: Quantitative Analysis and Mechanistic Insights

“…[1][2][3][4][5][6][7][8][9][10] The free energy liberated by the hydrolysis of ATP to ADP and inorganic phosphate is utilized to drive reactions requiring an input of free energy, such as muscle contraction. [10][11][12][13][14][15] Because green plants and microorganisms also capture and utilize energy by the same reaction, [16][17][18] the ATP-ADP thermodynamic cycle is the universal mode of energy exchange in biological systems.…”

Interpretation of the mechanism of action of antituberculosis drug bedaquiline based on a novel two‐ion theory of energy coupling in ATP synthesis

“…Addition of 50 μM CCCP uncoupler after ~4 min led to entry and binding of uncoupler anion in competition with succinate anion to a site on the a‐ or c‐subunit and to increasing reversal of the fluorescence quenching with time as progressive capture of protons by the CCCP anion took place in the vicinity of the binding sites due to the higher lipid solubility of the uncoupler (compared to physiological succinate anion), leading to formation of the uncharged form of the uncoupler and collapse of the ΔpH within 60 s. The uncharged species diffused away into the inside bulk aqueous phase, dissociated in that aqueous environment into uncoupler anion and proton, both of which were then pumped back by respiratory activity to restore the uncoupler gradient. The diffusion inwards of the neutral, uncharged species of uncoupler is very fast, compared to translocation separately of the individual ions and the slow conformational changes in the c‐subunit that these ion‐protein interactions induce . Hence the acceleration of cellular respiration that results in order to restore the ionic gradients by the redox side of OXPHOS, and how this phenotypic outcome arises originally from a drug–target interaction in F O is also clarified.…”

“…However, physiological ATP synthesis was demonstrated in the 1990s with single molecules of the ATP synthase purified and reconstituted into liposomes that contained no redox/photosystem complexes. Therefore, either no electrical potential is created, or a local potential, Δψ is created at the a–c interface in the membrane‐bound F O portion of ATP synthase …”

“…It is proposed here that a novel, chemically attractive explanation and resolution of the above crucial issues lies in the fact that under the experimental conditions of Hards et al and Lamprecht et al that employ an 80‐fold or a 30‐fold to 300‐fold higher concentration of bedaquiline respectively, relative to its minimum inhibitory concentration, an H + /K + antiport ionophore mechanism of bedaquiline and an uncoupling mode of action of the drug discussed above is operative, in accord with the central tenets of Nath's torsional mechanism in ATP synthase and two‐ion theory of energy coupling/uncoupling . The collapse of the H + and K + electrochemical gradients induced by the H + /K + exchange function of bedaquiline and the resulting uncoupling of ATP synthesis is responsible for the observed stimulation of oxygen consumption in M. smegmatis and M. tuberculosis …”

“…The activity of bedaquiline as an H + /K + ionophore releases H + ions into the inside bulk aqueous medium, and K + ions into the outside space, thereby dissipating the ΔpH and the ΔpK and creating a futile cycle of the ions that is uncoupled from ATP synthesis. As a result of the uncoupling of ATP synthesis caused by such ionophoric action of bedaquiline as an H + /K + antiporter, respiration will be accelerated compared to the physiological case in the absence of bedaquiline, when protons and physiological succinate counteranions A − /K + countercations translocate through F O , bind/unbind to/from their respective binding sites, and induce conformational changes in the c‐subunits of the c‐ring by means of ion‐protein interactions . However, bedaquiline does not interfere with the Δψ created by succinate translocation, A − (A) or K + translocation in the opposite direction (B) to their respective binding sites on the a‐subunit at the a–c interface in F O .…”