Adenosine triphosphate synthesis by electrochemical proton gradient in vesicles reconstituted from purified adenosine triphosphatase and phospholipids of thermophilic bacterium

Human F-ATP synthase as a drug target

Practical and conceptual barriers have kept human F-ATP synthase out of reach as a target for the treatment of human diseases. Although this situation has persisted for decades, it may change in the near future. In this review the principal functionalities of human F-ATP synthase--proton motive force / ATP interconversion, membrane bending and mitochondrial permeability transition--are surveyed in the context of their respective potential for pharmaceutical intervention. Further, the technical requirements necessary to allow drug designs that are effective at the multiple levels of functionality and modality of human F-ATP synthase are discussed. The structure-based development of gastric proton pump inhibitors is used to exemplify what might be feasible for human F-ATP synthase. And finally, four structural regions of the human F-ATP synthase are examined as potential sites for the development of structure based drug development.

ATP regeneration by ATPases for in vitro biotransformation

Adenosine triphosphate (ATP) regeneration is a significant step in both living cells and in vitro biotransformation (ivBT). Rotary motor ATP synthases (ATPases), which regenerate ATP in living cells, have been widely assembled in biomimetic structures for in vitro ATP synthesis. In this review, we present a comprehensive overview of ATPases, including the working principle, orientation and distribution density properties of ATPases, as well as the assembly strategies and applications of ATPase-based ATP regeneration modules. The original sources of ATPases for in vitro ATP regeneration include chromatophores, chloroplasts, mitochondria, and inverted Escherichia coli (E. coli) vesicles, which are readily accessible but unstable. Although significant advances have been made in the assembly methods for ATPase-artificial membranes in recent decades, it remains challenging to replicate the high density and orientation of ATPases observed in vivo using in vitro assembly methods. The use of bioproton pumps or chemicals for constructing proton motive forces (PMF) enables the versatility and potential of ATPase-based ATP regeneration modules. Additionally, overall robustness can be achieved via membrane component selection, such as polymers offering great mechanical stability, or by constructing a solid supporting matrix through layer-by-layer assembly techniques. Finally, the prospects of ATPase-based ATP regeneration modules can be expected with the technological development of ATPases and artificial membranes.

ATP synthesis in an ancient ATP synthase at low driving forces

SignificanceThe ATP synthases of many anaerobic archaea have an unusual motor subunit c that otherwise is only found in eukaryotic V₁V_O ATPases. The evolutionary switch from synthase to hydrolase is thought to be caused by a doubling of the rotor subunit c, followed by a loss of the ion binding site. By purification and reconstitution of an ATP synthase with a V-type c subunit, we have unequivocally demonstrated, against expectations, the capability of such an enzyme to synthesize ATP at physiological relevant driving forces of 90 to 150 mV. This is the long-awaited answer to an eminent question in microbial energetics and physiology, especially for life near the thermodynamic limit of ATP synthesis.

Electrophysiological Characterization of Microbial Rhodopsin Transport Properties: Electrometric and ΔpH Measurements Using Planar Lipid Bilayer, Collodion Film, and Fluorescent Probe Approaches

Electrophysiological approaches to the study of the activity of retinal-containing protein bacteriorhodopsin (bR) or other proteins of this family are based usually on measurements of electrical current through a planar bilayer lipid membrane (BLM) with proteoliposomes attached to the BLM surface at one side of the membrane. Here, we describe the measurements of the pumping activity of bR and channelrhodopsin 2 (ChR2) with special attention to the study of voltage dependence of the light-induced currents. Strong voltage dependence of ChR2 suggests light-triggered ion channel activity of ChR2. We also describe electrophysiological measurements with the help of collodion film instead of BLM for the measurements of fast stages of a rhodopsin photocycle as well as the estimation of the activity of proteoliposomes without a macro membrane using fluorescent probes such as oxonol VI or 9-aminoacridine.

A protet-based, protonic charge transfer model of energy coupling in oxidative and photosynthetic phosphorylation

Textbooks of biochemistry will explain that the otherwise endergonic reactions of ATP synthesis can be driven by the exergonic reactions of respiratory electron transport, and that these two half-reactions are catalyzed by protein complexes embedded in the same, closed membrane. These views are correct. The textbooks also state that, according to the chemiosmotic coupling hypothesis, a (or the) kinetically and thermodynamically competent intermediate linking the two half-reactions is the electrochemical difference of protons that is in equilibrium with that between the two bulk phases that the coupling membrane serves to separate. This gradient consists of a membrane potential term Δψ and a pH gradient term ΔpH, and is known colloquially as the protonmotive force or pmf. Artificial imposition of a pmf can drive phosphorylation, but only if the pmf exceeds some 150-170mV; to achieve in vivo rates the imposed pmf must reach 200mV. The key question then is 'does the pmf generated by electron transport exceed 200mV, or even 170mV?' The possibly surprising answer, from a great many kinds of experiment and sources of evidence, including direct measurements with microelectrodes, indicates it that it does not. Observable pH changes driven by electron transport are real, and they control various processes; however, compensating ion movements restrict the Δψ component to low values. A protet-based model, that I outline here, can account for all the necessary observations, including all of those inconsistent with chemiosmotic coupling, and provides for a variety of testable hypotheses by which it might be refined.

Mitochondrial F-ATP synthase as the permeability transition pore

The current state of research on the mitochondrial permeability transition pore (PTP) can be described in terms of three major problems: molecular identity, atomic structure and gating mechanism. In this review these three problems are discussed in the light of recent findings with special emphasis on the discovery that the PTP is mitochondrial F-ATP synthase (mtF_oF₁). Novel features of the mitochondrial F-ATP synthase emerging from the success of single particle cryo electron microscopy (cryo-EM) to determine F-ATP synthase structures are surveyed along with their possible involvement in pore formation. Also, current findings from the gap junction field concerning the involvement of lipids in channel closure are examined. Finally, an earlier proposal denoted as the 'Death Finger' is discussed as a working model for PTP gating.

An update of the chemiosmotic theory as suggested by possible proton currents inside the coupling membrane

Understanding how biological systems convert and store energy is a primary purpose of basic research. However, despite Mitchell's chemiosmotic theory, we are far from the complete description of basic processes such as oxidative phosphorylation (OXPHOS) and photosynthesis. After more than half a century, the chemiosmotic theory may need updating, thanks to the latest structural data on respiratory chain complexes. In particular, up-to date technologies, such as those using fluorescence indicators following proton displacements, have shown that proton translocation is lateral rather than transversal with respect to the coupling membrane. Furthermore, the definition of the physical species involved in the transfer (proton, hydroxonium ion or proton currents) is still an unresolved issue, even though the latest acquisitions support the idea that protonic currents, difficult to measure, are involved. Moreover, F_oF₁-ATP synthase ubiquitous motor enzyme has the peculiarity (unlike most enzymes) of affecting the thermodynamic equilibrium of ATP synthesis. It seems that the concept of diffusion of the proton charge expressed more than two centuries ago by Theodor von Grotthuss is to be taken into consideration to resolve these issues. All these uncertainties remind us that also in biology it is necessary to consider the Heisenberg indeterminacy principle, which sets limits to analytical questions.

Hypothesis of lipid-phase-continuity proton transfer for aerobic ATP synthesis

The basic processes harvesting chemical energy for life are driven by proton (H(+)) movements. These are accomplished by the mitochondrial redox complex V, integral membrane supramolecular aggregates, whose structure has recently been described by advanced studies. These did not identify classical aqueous pores. It was proposed that H(+) transfer for oxidative phosphorylation (OXPHOS) does not occur between aqueous sources and sinks, where an energy barrier would be insurmountable. This suggests a novel hypothesis for the proton transfer. A lipid-phase-continuity H(+) transfer is proposed in which H(+) are always bound to phospholipid heads and cardiolipin, according to Mitchell's hypothesis of asymmetric vectorial H(+) diffusion. A phase separation is proposed among the proton flow, following an intramembrane pathway, and the ATP synthesis, occurring in the aqueous phase. This view reminiscent of Grotthus mechanism would better account for the distance among the Fo and F1 moieties of FoF1-ATP synthase, for its mechanical coupling, as well as the necessity of a lipid membrane. A unique active role for lipids in the evolution of life can be envisaged. Interestingly, this view would also be consistent with the evidence of an OXPHOS outside mitochondria also found in non-vesicular membranes, housing the redox complexes.

Efficient ATP synthesis by thermophilic Bacillus FoF1-ATP synthase

F(o)F(1)-ATP synthase (F(o)F(1)) synthesizes ATP in the F(1) portion when protons flow through F(o) to rotate the shaft common to F(1) and F(o). Rotary synthesis in isolated F(1) alone has been shown by applying external torque to F(1) of thermophilic origin. Proton-driven ATP synthesis by thermophilic Bacillus PS3 F(o)F(1) (TF(o)F(1)), however, has so far been poor in vitro, of the order of 1 s(-1) or less, hampering reliable characterization. Here, by using a mutant TF(o)F(1) lacking an inhibitory segment of the ε-subunit, we have developed highly reproducible, simple procedures for the preparation of active proteoliposomes and for kinetic analysis of ATP synthesis, which was driven by acid-base transition and K(+)-diffusion potential. The synthesis activity reached ∼ 16 s(-1) at 30 °C with a Q(10) temperature coefficient of 3-4 between 10 and 30 °C, suggesting a high level of activity at the physiological temperature of ∼ 60 °C. The Michaelis-Menten constants for the substrates ADP and inorganic phosphate were 13 μM and 0.55 mM, respectively, which are an order of magnitude lower than previous estimates and are suited to efficient ATP synthesis.

ATP photosynthetic vesicles for light-driven bioprocesses

We prepared ATP photosynthetic vesicles from inside-out membranes of Escherichia coli cells that express delta-rhodopsin (a novel light-driven H(+) transporter) and TF(0)F(1)-ATP synthase (a thermo-stable ATP synthase). These vesicles showed light-dependent ATP synthesis. Furthermore, coupling the ATP photosynthetic vesicles with an ATP-hydrolyzing hexokinase enabled light-dependent glucose consumption. The ATP photosynthetic vesicles indicate their potential to applied to light-driven ATP-regenerating bioprocess for various ATP-hydrolyzing bioproductions.

Proton transport coupled ATP synthesis by the purified yeast H+ -ATP synthase in proteoliposomes

The H(+)/ATP synthase from yeast mitochondria, MF₀F₁, was purified and reconstituted into liposomes prepared from phosphatidylcholine and phosphatidic acid. Analysis by mass spectrometry revealed the presence of all subunits of the yeast enzyme with the exception of the K-subunit. The MF₀F₁ liposomes were energized by acid-base transitions (DeltapH) and a K(+)/valinomycin diffusion potential (Deltaphi). ATP synthesis was completely abolished by the addition of uncouplers as well as by the inhibitor oligomycin. The rate of ATP synthesis was optimized as a function of various parameters and reached a maximum value (turnover number) of 120s⁻¹ at a transmembrane pH difference of 3.2 units (at pH(in)=4.8 and pH(out)=8.0) and a Deltaphi of 133mV (Nernst potential). Functional studies showed that the monomeric MF₀F₁, was fully active in ATP synthesis. The turnover increased in a sigmoidal way with increasing internal and decreasing external proton concentration. The dependence of the turnover on the phosphate concentration and the dependence of K(M) on pH(out) indicated that the substrate for ATP synthesis is the monoanionic phosphate species H₂PO⁻₄.

ATP synthase: from single molecule to human bioenergetics

ATP synthase (F(o)F(1)) consists of an ATP-driven motor (F(1)) and a H(+)-driven motor (F(o)), which rotate in opposite directions. F(o)F(1) reconstituted into a lipid membrane is capable of ATP synthesis driven by H(+) flux. As the basic structures of F(1) (alpha(3)beta(3)gammadeltaepsilon) and F(o) (ab(2)c(10)) are ubiquitous, stable thermophilic F(o)F(1) (TF(o)F(1)) has been used to elucidate molecular mechanisms, while human F(1)F(o) (HF(1)F(o)) has been used to study biomedical significance. Among F(1)s, only thermophilic F(1) (TF(1)) can be analyzed simultaneously by reconstitution, crystallography, mutagenesis and nanotechnology for torque-driven ATP synthesis using elastic coupling mechanisms. In contrast to the single operon of TF(o)F(1), HF(o)F(1) is encoded by both nuclear DNA with introns and mitochondrial DNA. The regulatory mechanism, tissue specificity and physiopathology of HF(o)F(1) were elucidated by proteomics, RNA interference, cytoplasts and transgenic mice. The ATP synthesized daily by HF(o)F(1) is in the order of tens of kilograms, and is primarily controlled by the brain in response to fluctuations in activity.

Essentials for ATP synthesis by F1F0 ATP synthases

The majority of cellular energy in the form of adenosine triphosphate (ATP) is synthesized by the ubiquitous F(1)F(0) ATP synthase. Power for ATP synthesis derives from an electrochemical proton (or Na(+)) gradient, which drives rotation of membranous F(0) motor components. Efficient rotation not only requires a significant driving force (DeltamuH(+)), consisting of membrane potential (Deltapsi) and proton concentration gradient (DeltapH), but also a high proton concentration at the source P side. In vivo this is maintained by dynamic proton movements across and along the surface of the membrane. The torque-generating unit consists of the interface of the rotating c ring and the stator a subunit. Ion translocation through this unit involves a sophisticated interplay between the c-ring binding sites, the stator arginine, and the coupling ions on both sides of the membrane. c-ring rotation is transmitted to the eccentric shaft gamma-subunit to elicit conformational changes in the catalytic sites of F(1), leading to ATP synthesis.

Functional asymmetry of the F(0) motor in bacterial ATP synthases

F(1)F(0) ATP synthases use the electrochemical potential of H(+) or Na(+) across biological membranes to synthesize ATP by a rotary mechanism. In bacteria, the enzymes can act in reverse as ATP-driven ion pumps creating the indispensable membrane potential. Here, we demonstrate that the F(0) parts of a Na(+)- and H(+)-dependent enzyme display major asymmetries with respect to their mode of operation, reflected by the requirement of approximately 100 times higher Na(+) or H(+) concentrations for the synthesis compared with the hydrolysis of ATP. A similar asymmetry is observed during ion transport through isolated F(0) parts, indicating different affinities for the binding sites in the a/c interface. Together with further data, we propose a model that provides a rationale for a differential usage of membrane potential and ion gradient during ATP synthesis as observed experimentally. The functional asymmetry might also reflect an important property of the ATP synthesis mechanism in vivo. In Escherichia coli, we observed respiratory chain-driven ATP production at pH 7-8, while P-site pH values < 6.5 were required for ATP synthesis in vitro. This discrepancy is discussed with respect to the hypothesis that during respiration lateral proton diffusion could lead to significant acidification at the membrane surface.

Stochastic rotational catalysis of proton pumping F-ATPase

F-ATPases synthesize ATP from ADP and phosphate coupled with an electrochemical proton gradient in bacterial or mitochondrial membranes and can hydrolyse ATP to form the gradient. F-ATPases consist of a catalytic F1 and proton channel F0 formed from the alpha3beta3gammadelta and ab2c10 subunit complexes, respectively. The rotation of gammaepsilonc10 couples catalyses and proton transport. Consistent with the threefold symmetry of the alpha3beta3 catalytic hexamer, 120 degrees stepped revolution has been observed, each step being divided into two substeps. The ATP-dependent revolution exhibited stochastic fluctuation and was driven by conformation transmission of the beta subunit (phosphate-binding P-loop/alpha-helix B/loop/beta-sheet4). Recent results regarding mechanically driven ATP synthesis finally proved the role of rotation in energy coupling.

Unique rotary ATP synthase and its biological diversity

F1F0 ATP synthases convert energy stored in an electrochemical gradient of H+ or Na+ across the membrane into mechanical rotation, which is subsequently converted into the chemical bond energy of ATP. The majority of cellular ATP is produced by the ATP synthase in organisms throughout the biological kingdom and therefore under diverse environmental conditions. The ATP synthase of each particular cell is confronted with specific challenges, imposed by the specific environment, and thus by necessity must adapt to these conditions for optimal operation. Examples of these adaptations include diverse mechanisms for regulating the ATP hydrolysis activity of the enzyme, the utilization of different coupling ions with distinct ion binding characteristics, different ion-to-ATP ratios reflected by variations in the size of the rotor c ring, the mode of ion delivery to the binding sites, and the different contributions of the electrical and chemical gradients to the driving force.

Mitochondrial ATPase

Considerable progress has been made in recent years in our understanding of the phosphorylating apparatus in mitochondria, chloroplasts, and bacteria. It has become clear that the structure and the function of the ATP synthesizing apparatus in these widely divergent organisms is similar if not virtually identical. The subunit composition of F1, its molecular architecture, the location and function of substrate binding sites, as well as putative control sites, understanding of the component parts of the oligomycin-sensitive ATPase complex, and the role of these components in the function of the complex all are under active investigation in many laboratories. The developing information and the new insights provided have begun to permit experimental approaches, at the molecular level, to the mode of action of the ATPase in electron-transport-coupled ATP synthesis.

Biochemical and electron microscopic characterization of the F1F0 ATP synthase from the hyperthermophilic eubacterium Aquifex aeolicus

The F(1)F(0) ATP synthase has been purified from the hyperthermophilic eubacterium Aquifex aeolicus and characterized. Its subunits have been identified by MALDI-mass spectrometry through peptide mass fingerprinting and MS/MS. It contains the canonical subunits alpha, beta, gamma, delta and epsilon of F(1) and subunits a and c of F(0). Two versions of the b subunit were found, which show a low sequence homology to each other. Most likely they form a heterodimer. An electron microscopic single particle analysis revealed clear structural details, including two stalks connecting F(1) and F(0). In several orientations the central stalk appears to be tilted and/or kinked. It is unclear whether there is a direct connection between the peripheral stalk and the delta subunit.

ATP synthase that lacks F0a-subunit: isolation, properties, and indication of F0b2-subunits as an anchor rail of a rotating c-ring

In a rotary motor F1F0-ATP synthase, F0 works as a proton motor; the oligomer ring of F0c-subunits (c-ring) rotates relative to the F0ab2 domain as protons pass through F0 down the gradient. F0ab2 must exert dual functions during rotation, that is, sliding the c-ring (motor drive) while keeping the association with the c-ring (anchor rail). Here we have isolated thermophilic F1F0(-a) which lacks F0a. F1F0(-a) has no proton transport activity, and F0(-a) does not work as a proton channel. Interestingly, ATPase activity of F1F0(-a) is greatly suppressed, even though its F1 sector is intact. Most likely, F0b2 associates with the c-ring as an anchor rail in the intact F1F0; without F0a, this association prevents rotation of the c-ring (and hence the gamma-subunit), which disables ATP hydrolysis at F1. Functional F1F0 is easily reconstituted from purified F0a and F1F0(-a), and thus F0a can bind to its proper location on F1F0(-a) without a large rearrangement of other-subunits.

ATP synthase--a marvellous rotary engine of the cell

ATP synthase can be thought of as a complex of two motors--the ATP-driven F1 motor and the proton-driven Fo motor--that rotate in opposite directions. The mechanisms by which rotation and catalysis are coupled in the working enzyme are now being unravelled on a molecular scale.

Operation of the F(0) motor of the ATP synthase

ATP, the universal carrier of cell energy is manufactured from ADP and phosphate by the enzyme ATP synthase using the energy stored in a transmembrane ion gradient. The two components of the ion gradient (DeltapH or DeltapNa(+)) and the electrical potential difference Deltapsi are thermodynamically but not kinetically equivalent. In contrast to accepted wisdom, the electrical component is kinetically indispensable not only for bacterial ATP synthases but also for that from chloroplasts. Recent biochemical studies with the Na(+)-translocating ATP synthase of Propionigenium modestum have given a good idea of the ion translocation pathway in the F(0) motor. Taken together with biophysical data, the operating principles of the motor have been delineated.

Reconstitution of beef heart mitochondrial F0F1 in reverse phase evaporation vesicles

Beef heart mitochondrial F0F1 was reconstituted in proteoliposomes by a new procedure. MF0F1 was inserted in preformed reverse phase evaporation vesicles of large diameters prepared from asolectin (MF0F1-REV). Reconstitution was mediated by Triton X-100, which was subsequently removed by treatment with Bio-Beads. Parameters which resulted in optimal reconstitution were described. The MF0F1-REV proteoliposomes catalyzed an exchange between Pi and ATP and were capable of proton pumping. Both reactions were inhibited by oligomycin and uncoupler of oxidative phosphorylation. The range of Pi-ATP exchange activity of the proteoliposomes (70-110 nmol min[-1] mg[-1]) compared favorably with activities obtained in vesicles reconstituted by cholate dialysis or cholate dilution. The most important aspect of this method is that, unlike other reconstitution methods, exogenous F1 and other coupling factors are not required to obtain high Pi-ATP exchange activity by MF0F1-REV. This simple and rapid reconstitution procedure should be useful for future studies dealing with functional analysis of MF0F1.

ATP synthesis catalyzed by the ATP synthase of Escherichia coli reconstituted into liposomes

The H(+)-translocating F0F1-ATPase from Escherichia coli (EF0F1) was purified and reconstituted into preformed reverse-phase liposomes prepared from egg yolk phosphatidylcholine/phosphatidic acid. The EF0F1 liposomes were energized by an acid/base transition (pHout = 8.3; pHin = 5.0) and a superimposed K+/valinomycin diffusion potential ([K+]out = 100 mM; [K+]in = 0.6 mM) yielding a maximum rate (turnover number) of ATP synthesis of 27 +/- 8 mol ATP . mol EF0F1(-1) . s-1), i.e. 27 +/- 8 s-1. This reaction was inhibited by NH4Cl or by addition of the F0F1 inhibitor N,N'-dicyclohexylcarbodiimide. The rate of ATP synthesis measured as a function of the phosphate and ADP concentrations, can be described by Michaelis-Menten kinetics with a Km of 0.7 +/- 0.2 mM for phosphate ([ADP] = 200 microM) and a Km of 27 +/- 7 microM for ADP ([phosphate] = 5 mM), respectively.

ATP synthesis in chromatophores driven by artificially induced ion gradients

An electrochemical potential difference for protons (delta mu H+) across the membrane of bacterial chromatophores was induced by an artificially generated pH difference (delta pH) and a K+/valinomycin diffusion potential, delta phi. The initial rate of ATP synthesis was measured with a rapid-mixing quenched-flow apparatus in the time range between 70 ms and 30 s after the acid-base transition. The rate of ATP synthesis depends exponentially on delta pH. Increasing diffusion potentials shift the delta pH dependency to lower delta pH values. Diffusion potentials were calculated from the Goldman equation. Using estimated permeability coefficients, the rate of ATP synthesis depends only on the electrochemical potential difference of protons irrespective of the relative contribution of delta pH and delta phi.

ATP-synthesis by proteoliposomes incorporating Rhodospirillum rubrum F0F1 as measured with firefly luciferase: dependence on delta psi and delta pH

ATP-synthesis catalyzed by proteoliposomes incorporating Rhodospirillum rubrum F0F1 was driven by artificially applied electrochemical proton gradients. The time-course of ATP-synthesis was followed continuously by means of firefly luciferase. Correction methods were developed which allow one to calculate the initial rate of ATP-synthesis from the observed luminescence kinetics. The following results were obtained: (1) ATP-synthesis occurred above a threshold delta mu H+ of 90 mV; this threshold is not imposed by the activation requirement of the enzyme; (2) delta psi and delta pH appear to be equivalent as driving forces for ATP-synthesis if allowance is made for the effect of the electrical capacitance of the liposome membrane on the distribution of K+ at equilibrium; and (3) the highest rate observed so far is 200 mol ATP per mol F0F1 per s.

Unique relationships between the rates of oxidation and phosphorylation and the protonmotive force in rat-liver mitochondria

The rate of ATP synthesis (JP) in isolated rat-liver mitochondria was strongly dependent on the magnitude of the protonmotive force (delta mu H+) across the mitochondrial inner membrane. Addition of different concentrations of various uncouplers or malonate to mitochondrial incubations in State 3 led to a depression of delta mu H+ and a concomitant decrease in JP. A unique relationship between JP and delta mu H+ was obtained, which was independent of the way in which delta mu H+ was varied. This unique relationship was observed when K+ (in the presence of valinomycin) was used as a probe for delta psi. Different relationships between JP and delta mu H+ were observed when K+ was used as a probe for delta psi and when K+ was measured after separation of the mitochondria by centrifugation without silicone oil. This led to a serious underestimation of delta psi, specifically when uncouplers were present, and non-unique flow-force relationships were thus obtained. Anomalous relationships between JP and delta mu H+ were also found when TPMP+ was used as a probe for delta psi. However, in uncoupler incubations the presence of TBP- strongly affected the TPMP+ accumulation ratio without any effect on the K+ accumulation or on JP and in the presence of TBP- unique relationships between JP and delta mu H+ were again obtained. This indicates that the accumulation of TPMP+ inside the mitochondria is not a straightforward function of delta psi but also depends on conditions like the presence of TBP- or uncouplers. We conclude that there is a unique relationship between the rate of phosphorylation and the protonmotive force in mitochondria and that under some conditions the behaviour of TPMP+ is anomalous.

Proton concentration jumps and generation of transmembrane pH-gradients by photolysis of 4-formyl-6-methoxy-3-nitrophenoxyacetic acid

Proton concentration gradients across membranes are important for many biological energy transducing processes. The kinetics of proton dependent processes can be studied by pH-jump methods in which protons are photochemically released. In the following we describe the synthesis and the properties of photolabile 4-formyl-6-methoxy-3-nitrophenoxyacetic acid, a 'caged proton'. The synthesis is based on vanillin, which is alkylated with chloroacetic acid to give a carboxylic acid (pK = 2.72). In a second step a nitro group ortho to the formyl group is introduced. Photochemical proton release occurs by a reaction mechanism analogous to the well known photochemical formation of 2-nitrosobenzoic acid from 2-nitrobenzaldehyde. The pK values of the photoproduct are 0.75 and 2.76, respectively, thus allowing the use of the compound in a wide pH-range. The quantum yield is 0.18, lower than in the case of the 2-nitrobenzaldehyde/2-nitrosobenzoic acid system (phi = 0.5). The release of the proton in a flash photolysis experiment occurs within less than 1 microseconds. The spectrum of photolabile compound has absorption maxima at 263 nm and 345 nm, respectively. Its permeability across a lipid bilayer membrane is very low (permeability coefficient Pd approximately equal to 10(-9) cm.s-1 at pH 8) so that transmembrane proton concentration gradients can be generated.

Correlation of the turnover number of the ATP synthase in liposomes with the proton flux and the proton potential across the membrane

The fluorescent indicator pyranine was used for recording the internal pH of liposomes. The proton permeability was deduced from the velocity of the internal pH increase which was caused by shifting the external pH from 7 to 9. From valinomycin titration of the proton permeability in the presence of internal and external KCl (0.1 M), the permeability coefficient of H+ (PH) was obtained as 10(-4) cm/s at 22 degrees C. The coefficient was twice this value with the ATP synthase isolated from Wolinella succinogenes present in the liposomal membrane (10 mg protein/g phospholipid). ADP and phosphate had no effect on the latter PH. The protonophore TTFB (5 mumol/g phospholipid) increased the PH by 3 orders of magnitude. The permeability coefficients of H+ and K+ were used for calculating the delta uH and the proton flux associated with the phosphorylation which was driven by gradients of H+ and K+. For the conditions of limiting permeability of K+, the following conclusions were drawn. (1) In the steady state of rapid ion flux, the electrical potential across the liposomal membrane as calculated according to the Goldman equation, is directed opposite to the corresponding Nernst potential which is calculated from the K+ gradient. (2) The maximum turnover numbers of phosphorylation require a delta uH of 200-220 mV across the liposomal membrane. These values of delta uH and the corresponding turnover numbers are close to those brought about by the bacterial electron transport and the coupled phosphorylation. (3) The velocity of phosphorylation is linearly related to the proton flux. The slope of the line can be explained on the basis of an H+/ATP ratio of approx. 3.

ATP synthase-mediated proton fluxes and phosphorylation in rat liver mitochondria: dependence on delta mu H

The dependence of the proton flux through the ATP synthases of rat liver mitochondria on a driving force composed mainly of a potassium diffusion potential was determined and compared with the relationship between rate of phosphorylation and delta mu H given by titrations with the respiratory inhibitor malonate. The two functions are in good agreement in the lower part of the delta mu H range covered. However, the maximal proton fluxes through the ATP synthases are much lower than needed to account for the rate of State 3 phosphorylation sustained by the same mitochondria oxidizing succinate. Possible reasons for this behavior are discussed.

Exogenous energy supply to the plasma membrane of dark anaerobic cyanobacterium Anacystis nidulans: thermodynamic and kinetic characterization of the ATP synthesis effected by an artificial proton motive force

The net synthesis of ATP in dark anaerobic cells of Anacystis nidulans subjected to acid jumps and/or valinomycin pulses was characterized thermodynamically and kinetically. Maximum initial rates of 75 nmol ATP/min per mg dry weight at an applied proton motive force of -350 mV were obtained, the flow-force relationship (rate of ATP synthesis vs applied proton motive force) being linear between -240 and -320 mV irrespective of the source of the proton motive force. The pulse-induced ATP synthesis was inhibited by uncouplers (H+ ionophores) and F0F1-ATPase inhibitors but not by KCN or CO. In order to obtain maximum rates of pulse-induced ATP synthesis both a favorable stationary delta psi (-100 mV at pHo 9, preceding the acid jumps) and a favorable stationary delta pH (+2 units at pHo 4.1, preceding the valinomycin pulse) of the plasma membrane were obligatory, the effects of delta psi and delta pH being strictly additive. Moreover, the pulse-induced ATP synthesis required a minimum total proton motive force of -200 to -250 mV across the plasma membrane; it also required low preexisting phosphorylation potentials corresponding to -400 mV in dark anaerobic, i.e., energy-depleted, cells. The results are discussed in terms of both a reversible H+-ATPase and a respiratory electron transport system occurring in the plasma membrane of intact Anacystis nidulans.

Phosphorylation and phosphate-ATP exchange catalyzed by the ATP synthase isolated from Wolinella succinogenes

The ATP synthase, isolated from Wolinella (formerly Vibrio) succinogenes could be fully incorporated into liposomes without significant cleavage of the enzyme or loss of activity. These proteoliposomes, but not the isolated enzyme, catalyzed phosphate-ATP exchange and the phosphorylation of ADP which was driven by an artificially imposed delta mu H across the liposomal membrane. Phosphorylation driven by light was catalyzed by proteoliposomes containing also bacteriorhodopsin. The three activities were similarly sensitive to protonophores or dicyclohexylcarbodiimide. This sensitivity was similar to that of the electron-transport-driven phosphorylation catalyzed by bacterial membrane vesicles. With a delta mu H value 280 mV to drive phosphorylation the turnover number of the enzyme was in the same order of magnitude as that measured in the electron-transport-driven phosphorylation catalyzed by the bacterial membrane. When the delta mu H was below 150 mV, the phosphorylation activity of the incorporated enzyme was two orders of magnitude slower, and was about as fast as light-driven phosphorylation or as the exchange reaction.

Quantum-mechanical descriptions of proton transfer in biosystems containing hydrogen-bonded chains

A mechanism of proton transfer along the proton channel of (F0) ATP-synthetase of a membrane is suggested. In the small polaron model the charged fault (an excess of protons or a proton hole) transfer is considered in a longitudinal electric field along an assumed chain which is formed by hydroxyl groups connected by strong H-bonded chains. A number of kinetic parameters are estimated. The theoretical data are compared with the experimental results.

Voltage-dependent proton fluxes in liposomes

Liposomes containing buffered KCl were prepared from bacterial lipids, were diluted into K+-free media and were treated with valinomycin to induce the formation of a diffusion potential (delta psi). Upon formation of such a potential, substantial proton influx was observed, as assayed by the quenching of 9-aminoacridine fluorescence. Complete reversal of fluorescence quenching occurred when the potential was collapsed by addition of KCl or when methylamine was added. Studies of proton influx as a function of the theoretical magnitude of the delta psi indicated that the phenomenon occurred only above a delta psi of about -60 mV. Establishment of a Na+ diffusion potential also resulted in proton influx. Treatment of K+-loaded liposomes with N,N'-dicyclohexylcarbodiimide did not reduce the delta psi-dependent proton influx. Moreover, proton influx could be demonstrated upon imposition of a diffusion potential in liposomes prepared from a synthetic lipid. The proton fluxes associated with generation of a diffusion potential in liposomes may complicate studies of reconstituted systems in which proton translocation should occur, and may affect the magnitude of the electrochemical proton gradient that is operant under some conditions.