Studies on the mechanism of oxidative phosphorylation: effects of specific F0 modifiers on ligand-induced conformation changes of F1

Defueling the cancer: ATP synthase as an emerging target in cancer therapy

Reprogramming of cellular metabolism is a hallmark of cancer. Mitochondrial ATP synthase (MAS) produces most of the ATP that drives the cell. High expression of the MAS-composing proteins is found during cancer and is linked to a poor prognosis in glioblastoma, ovarian cancer, prostate cancer, breast cancer, and clear cell renal cell carcinoma. Cell surface-expressed ATP synthase, translocated from mitochondrion to cell membrane, involves the angiogenesis, tumorigenesis, and metastasis of cancer. ATP synthase has therefore been considered a therapeutic target. We review recent various ATP synthase inhibitors that suppress tumor growth and are being tested for the clinic.

Fluorescent Antibiotics: New Research Tools to Fight Antibiotic Resistance

Better understanding how multidrug-resistant (MDR) bacteria can evade current and novel antibiotics requires a better understanding of the chemical biology of antibiotic action. This necessitates using new tools and techniques to advance our knowledge of bacterial responses to antibiotics, ideally in live cells in real time, to selectively investigate bacterial growth, division, metabolism, and resistance in response to antibiotic challenge. In this review, we discuss the preparation and biological evaluation of fluorescent antibiotics, focussing on how these reporters and assay methods can help elucidate resistance mechanisms. We also examine the potential utility of such probes for real-time in vivo diagnosis of infections.

Mitochondrial ATP synthase: architecture, function and pathology

Human mitochondrial (mt) ATP synthase, or complex V consists of two functional domains: F(1), situated in the mitochondrial matrix, and F(o), located in the inner mitochondrial membrane. Complex V uses the energy created by the proton electrochemical gradient to phosphorylate ADP to ATP. This review covers the architecture, function and assembly of complex V. The role of complex V di-and oligomerization and its relation with mitochondrial morphology is discussed. Finally, pathology related to complex V deficiency and current therapeutic strategies are highlighted. Despite the huge progress in this research field over the past decades, questions remain to be answered regarding the structure of subunits, the function of the rotary nanomotor at a molecular level, and the human complex V assembly process. The elucidation of more nuclear genetic defects will guide physio(patho)logical studies, paving the way for future therapeutic interventions.

Modulation at a distance of proton conductance through the Saccharomyces cerevisiae mitochondrial F1F0-ATP synthase by variants of the oligomycin sensitivity-conferring protein containing substitutions near the C-terminus

We have sought to elucidate how the oligomycin sensitivity-conferring protein (OSCP) of the mitochondrial F(1)F(0)-ATP synthase (mtATPase) can influence proton channel function. Variants of OSCP, from the yeast Saccharomyces cerevisiae, having amino acid substitutions at a strictly conserved residue (Gly166) were expressed in place of normal OSCP. Cells expressing the OSCP variants were able to grow on nonfermentable substrates, albeit with some increase in generation time. Moreover, these strains exhibited increased sensitivity to oligomycin, suggestive of modification in functional interactions between the F(1) and F(0) sectors mediated by OSCP. Bioenergetic analysis of mitochondria from cells expressing OSCP variants indicated an increased respiratory rate under conditions of no net ATP synthesis. Using specific inhibitors of mtATPase, in conjunction with measurement of changes in mitochondrial transmembrane potential, it was revealed that this increased respiratory rate was a result of increased proton flux through the F(0) sector. This proton conductance, which is not coupled to phosphorylation, is exquisitely sensitive to inhibition by oligomycin. Nevertheless, the oxidative phosphorylation capacity of these mitochondria from cells expressing OSCP variants was no different to that of the control. These results suggest that the incorporation of OSCP variants into functional ATP synthase complexes can display effects in the control of proton flux through the F(0) sector, most likely mediated through altered protein-protein contacts within the enzyme complex. This conclusion is supported by data indicating impaired stability of solubilized mtATPase complexes that is not, however, reflected in the assembly of functional enzyme complexes in vivo. Given a location for OSCP atop the F(1)-alpha(3)beta(3) hexamer that is distant from the proton channel, then the modulation of proton flux by OSCP must occur "at a distance." We consider how subtle conformational changes in OSCP may be transmitted to F(0).

ATP synthase and the actions of inhibitors utilized to study its roles in human health, disease, and other scientific areas

ATP synthase, a double-motor enzyme, plays various roles in the cell, participating not only in ATP synthesis but in ATP hydrolysis-dependent processes and in the regulation of a proton gradient across some membrane-dependent systems. Recent studies of ATP synthase as a potential molecular target for the treatment of some human diseases have displayed promising results, and this enzyme is now emerging as an attractive molecular target for the development of new therapies for a variety of diseases. Significantly, ATP synthase, because of its complex structure, is inhibited by a number of different inhibitors and provides diverse possibilities in the development of new ATP synthase-directed agents. In this review, we classify over 250 natural and synthetic inhibitors of ATP synthase reported to date and present their inhibitory sites and their known or proposed modes of action. The rich source of ATP synthase inhibitors and their known or purported sites of action presented in this review should provide valuable insights into their applications as potential scaffolds for new therapeutics for human and animal diseases as well as for the discovery of new pesticides and herbicides to help protect the world's food supply. Finally, as ATP synthase is now known to consist of two unique nanomotors involved in making ATP from ADP and P(i), the information provided in this review may greatly assist those investigators entering the emerging field of nanotechnology.

Inefficient coupling between proton transport and ATP synthesis may be the pathogenic mechanism for NARP and Leigh syndrome resulting from the T8993G mutation in mtDNA

Mutations in the ATP6 gene of mtDNA (mitochondrial DNA) have been shown to cause several different neurological disorders. The product of this gene is ATPase 6, an essential component of the F1F0-ATPase. In the present study we show that the function of the F1F0-ATPase is impaired in lymphocytes from ten individuals harbouring the mtDNA T8993G point mutation associated with NARP (neuropathy, ataxia and retinitis pigmentosa) and Leigh syndrome. We show that the impaired function of both the ATP synthase and the proton transport activity of the enzyme correlates with the amount of the mtDNA that is mutated, ranging from 13-94%. The fluorescent dye RH-123 (Rhodamine-123) was used as a probe to determine whether or not passive proton flux (i.e. from the intermembrane space to the matrix) is affected by the mutation. Under state 3 respiratory conditions, a slight difference in RH-123 fluorescence quenching kinetics was observed between mutant and control mitochondria that suggests a marginally lower F0 proton flux capacity in cells from patients. Moreover, independent of the cellular mutant load the specific inhibitor oligomycin induced a marked enhancement of the RH-123 quenching rate, which is associated with a block in proton conductivity through F0 [Linnett and Beechey (1979) Inhibitors of the ATP synthethase system. Methods Enzymol. 55, 472-518]. Overall, the results rule out the previously proposed proton block as the basis of the pathogenicity of the mtDNA T8993G mutation. Since the ATP synthesis rate was decreased by 70% in NARP patients compared with controls, we suggest that the T8993G mutation affects the coupling between proton translocation through F0 and ATP synthesis on F1. We discuss our findings in view of the current knowledge regarding the rotary mechanism of catalysis of the enzyme.

Positively charged ceramide is a potent inducer of mitochondrial permeabilization

Ceramide-induced cell death is thought to be mediated by change in mitochondrial function, although the precise mechanism is unclear. Proposed models suggest that ceramide induces cell death through interaction with latent binding sites on the outer or inner mitochondrial membranes, followed by an increase in membrane permeability, as an intermediate step in ceramide signal propagation. To investigate these models, we developed a new generation of positively charged ceramides that readily accumulate in isolated and in situ mitochondria. Accumulated, positively charged ceramides increased inner membrane permeability and triggered release of mitochondrial cytochrome c. Furthermore, the positively charged ceramide-induced permeability increase was suppressed by cyclosporin A (60%) and 1,3-dicyclohexylcarbodiimide (90%). These observations suggest that the inner membrane permeability increase is due to activation of specific ion transporters, not the generalized loss of lipid bilayer barrier functions. The difference in sensitivity of ceramide-induced ion fluxes to inhibitors of mitochondrial transporters suggests activation of at least two transport systems: the permeability transition pore and the electrogenic H(+) channel. Our results indicate the presence of specific ceramide targets in the mitochondrial matrix, the occupation of which triggers permeability alterations of the inner and outer mitochondrial membranes. These findings also suggest a novel therapeutic role for positively charged ceramides.

Rotational coupling in the F0F1 ATP synthase

The F0F1 ATP synthase is a large multisubunit complex that couples translocation of protons down an electrochemical gradient to the synthesis of ATP. Recent advances in structural analyses have led to the demonstration that the enzyme utilizes a rotational catalytic mechanism. Kinetic and biochemical evidence is consistent with the expected equal participation of the three catalytic sites in the alpha 3 beta 3 hexamer, which operate in sequential, cooperative reaction pathways. The rotation of the core gamma subunit plays critical roles in establishing the conformation of the sites and the cooperative interactions. Mutational analyses have shown that the rotor subunits are responsible for coupling and in doing so transmit specific conformational information between transport and catalysis.

ATP synthase: a tentative structural model

Adenosine triphosphate (ATP) synthase produces ATP from ADP and inorganic phosphate at the expense of proton- or sodium-motive force across the respective coupling membrane in Archaea, Bacteria and Eucarya. Cation flow through the intrinsic membrane portion of this enzyme (Fo, subunits ab2c9-12) and substrate turnover in the headpiece (F1, subunits alpha3beta3 gammadeltaepsilon) are mechanically coupled by the rotation of subunit gamma in the center of the catalytic hexagon of subunits (alphabeta)3 in F1. ATP synthase is the smallest rotatory engine in nature. With respect to the headpiece alone, it probably operates with three steps. Partial structures of six out of its at least eight different subunits have been published and a 3-dimensional structure is available for the assembly (alphabeta)3gamma. In this article, we review the available structural data and build a tentative topological model of the holoenzyme. The rotor portion is proposed to consist of a wheel of at least nine copies of subunits c, epsilon and a portion of gamma as a spoke, and another portion of gamma as a crankshaft. The stator is made up from a, the transmembrane portion of b2, delta and the catalytic hexagon of (alphabeta)3. As an educated guess, the model may be of heuristic value for ongoing studies on this fascinating electrochemical-to-mechanical-to-chemical transducer.

Catalytic mechanism of F1-ATPase

The structure of the core catalytic unit of ATP synthase, alpha 3 beta 3 gamma, has been determined by X-ray crystallography, revealing a roughly symmetrical arrangement of alternating alpha and beta subunits around a central cavity in which helical portions of gamma are found. A low-resolution structural model of F0, based on electron spectroscopic imaging, locates subunit a and the two copies of subunit b outside of a subunit c oligomer. The structures of individual subunits epsilon and c (largely) have been solved by NMR spectroscopy, but the oligomeric structure of c is still unknown. The structures of subunits a and delta remain undefined, that of b has not yet been defined but biochemical evidence indicates a credible model. Subunits gamma, epsilon, b, and delta are at the interface between F1 and F0; gamma epsilon complex forms one element of the stalk, interacting with c at the base and alpha and beta at the top. The locations of b and delta are less clear. Elucidation of the structure F0, of the stalk, and of the entire F1F0 remains a challenging goal.

Turnover number of Escherichia coli F0F1 ATP synthase for ATP synthesis in membrane vesicles

The rate of ATP synthesized by the ATP synthase (F0F1-ATPase) is limited by the rate of energy production via the respiratory chain, when measured in everted membrane vesicles of an Escherichia coli atp wild-type strain. After energization of the membranes with NADH, fractional inactivation of F0F1 by the covalent inhibitor N,N'-dicyclohexylcarbodiimide allowed the rate of ATP synthesis/mol remaining active ATP synthase complexes to increase; the active ATP synthase complexes were calculated using ATP hydrolysis rates as the defining parameter. In addition, variation of the assay temperature revealed an increase of the ATP synthesis rate up to a temperature of 37 degrees C, the optimal growth temperature of E. coli. In parallel, the amount of F0F1 complexes present in membrane vesicles was determined by immunoquantitation to be 3.3 +/- 0.3% of the membrane protein for cells grown in rich medium and 6.6 +/- 0.3% for cells grown in minimal medium with glycerol as sole carbon and energy source. Based on these data, a turnover number for ATP synthesis of 270 +/- 40 s(-1) could be determined in the presence of 5% active F0F1 complexes. Therefore, these studies demonstrate that the ATP synthase complex of E. coli has, with respect to maximum rates, the same capacity as the corresponding enzymes of eukaryotic organells.

The F0F1-type ATP synthases of bacteria: structure and function of the F0 complex

Membrane-bound ATP synthases (F0F1-ATPases) of bacteria serve two important physiological functions. The enzyme catalyzes the synthesis of ATP from ADP and inorganic phosphate utilizing the energy of an electrochemical ion gradient. On the other hand, under conditions of low driving force, ATP synthases function as ATPases, thereby generating a transmembrane ion gradient at the expense of ATP hydrolysis. The enzyme complex consists of two structurally and functionally distinct parts: the membrane-integrated ion-translocating F0 complex and the peripheral F1 complex, which carries the catalytic sites for ATP synthesis and hydrolysis. The ATP synthase of Escherichia coli, which has been the most intensively studied one, is composed of eight different subunits, five of which belong to F1, subunits alpha, beta, gamma, delta, and epsilon (3:3:1:1:1), and three to F0, subunits a, b, and c (1:2:10 +/- 1). The similar overall structure and the high amino acid sequence homology indicate that the mechanism of ion translocation and catalysis and their mode of coupling is the same in all organisms.

Energetics of ATP dissociation from the mitochondrial ATPase during oxidative phosphorylation

The dissociation constant (KdATP) for ATP bound in the high affinity catalytic site of membrane-bound beef heart mitochondrial ATPase (F1) was calculated from the ratio of the rate constants for the reverse dissociation step (k-1) and the forward binding step (k+1). k-1 for ATP bound to submitochondrial particles or to submitochondrial particles washed with KCl so as to activate ATPase activity was accelerated by about five orders of magnitude during respiratory chain-linked oxidations of NADH. In the presence of NADH and 0.1 mM ADP, k-1 increased more than six orders of magnitude. These energy-dependent dissociations of ATP were sensitive to the uncoupler carbonyl cyanide p-trifluoromethyloxyphenylhydrazone. Only small changes in k+1 were observed in the presence of NADH or NADH and ADP. KdATP at 23 degrees C in the absence of NADH and ADP was 10(-12) M, in the presence of NADH, 3 microM, and in the presence of NADH and 0.1 mM ADP, 60 microM. Thus, the dissociation of ATP during the transition from non-energized to energized states was, under these conditions, accompanied by observed free energy changes of 8 and 9.7 kcal/mol, respectively.

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.

Hairpin folding of subunit c of F1Fo ATP synthase: 1H distance measurements to nitroxide-derivatized aspartyl-61

Subunit c from the F1Fo ATP synthase of Escherichia coli folds in a hairpinlike structure of two alpha-helices in a solution of chloroform-methanol-H2O, and thus resembles the structure predicted for the folded protein in the membrane. The relevance of the structure in solution to the native structure was demonstrated. Asp61 in the second helical arm was shown to retain its unique reactivity with dicyclohexylcarbodiimide (DCCD) in chloroform-methanol-H2O solution. Further, the protein purified from the Ile28-->Thr DCCD-resistant mutant proved to be less reactive with DCCD in solution. This suggested that the protein folded with Ile28 of the first helical arm close to Asp61 in the second helical arm. Subunit c in wild-type E. coli membranes was specifically labeled with a nitroxide analog of DCCD (NCCD), and the derivative protein was purified. DQF COSY spectra were recorded, and the distances between the paramagnetic nitroxide and resolved protons in the spectra were calculated based upon paramagnetic broadening of the 1H resonances. The paramagnetic contribution to T2 relaxation in the NCCD-labeled sample was calculated by an iterative computer-fitting method, where a control spectrum of a phenylhydrazine-reduced sample was broadened until the line shape of one-dimensional slices through each COSY cross-peak maximally mimicked the line shape of the paramagnetic sample. The distances calculated from paramagnetic broadening indicate that Ala24 and Ala25 in helix-1 lie close (ca. 12 A) to the derivatized Asp61 in helix-2. A model for the interaction of helices in the NCCD-modified protein was generated by restrained molecular mechanics and molecular dynamics using 25 distances of < 10-20 A derived from paramagnetic broadening in combination with 15 long-range nuclear Overhauser enhancement (NOE) restraints (2-5 A) for distances between helices and the 89 intrahelical NOEs that defined helical structure in the DCCD-modified protein.

Functional sites in F1-ATPases: location and interactions

This review focuses on the location and interaction of three functional sites in F1-ATPases. These are catalytic sites which are located in beta subunits, noncatalytic nucleotide-binding sites which are located at interfaces of alpha and beta subunits and modulate the hydrolytic activity of the enzyme, and a site that binds inhibitory amphipathic cations which is at an interface of alpha and beta subunits. The latter site may participate in transmission of conformational signals between catalytic sites in F1 and the proton-conducting apparatus of F0 in the intact ATP synthases.

The ATP synthase (F0-F1) complex in oxidative phosphorylation

The transmembrane electrochemical proton gradient generated by the redox systems of the respiratory chain in mitochondria and aerobic bacteria is utilized by proton translocating ATP synthases to catalyze the synthesis of ATP from ADP and P(i). The bacterial and mitochondrial H(+)-ATP synthases both consist of a membranous sector, F0, which forms a H(+)-channel, and an extramembranous sector, F1, which is responsible for catalysis. When detached from the membrane, the purified F1 sector functions mainly as an ATPase. In chloroplasts, the synthesis of ATP is also driven by a proton motive force, and the enzyme complex responsible for this synthesis is similar to the mitochondrial and bacterial ATP synthases. The synthesis of ATP by H(+)-ATP synthases proceeds without the formation of a phosphorylated enzyme intermediate, and involves co-operative interactions between the catalytic subunits.

Nucleotide-dependent and dicyclohexylcarbodiimide-sensitive conformational changes in the epsilon subunit of Escherichia coli ATP synthase

The rate of trypsin cleavage of the epsilon subunit of Escherichia coli F1F0 (ECF1F0) is shown to be ligand-dependent as measured by Western analysis using monoclonal antibodies. The cleavage of the epsilon subunit was rapid in the presence of ADP alone, ATP + EDTA, or AMP-PNP + Mg2+, but slow when Pi was added along with ADP + Mg2+ or when ATP + Mg2+ was added to generate ADP + Pi (+Mg2+) in the catalytic site. Trypsin treatment of ECF1Fo was also shown to increase enzymic activity on a time scale corresponding to that of the cleavage of the epsilon subunit, indicating that the epsilon subunit inhibits ATPase activity in ECF1Fo. The ligand-dependent conformational changes in the epsilon subunit were also examined in cross-linking experiments using the water-soluble carbodiimide 1-ethyl-3-[3-(dimethylamino)propyl]-carbodiimide (EDC). In the presence of ATP + Mg2+ or ADP + Pi + Mg2+, the epsilon subunit cross-linked product was much reduced. Prior reaction of ECF1Fo with dicyclohexylcarbodiimide (DCCD), under conditions in which only the Fo part was modified, blocked the conformational changes induced by ligand binding. When the enzyme complex was reacted with DCCD in ATP + EDTA, the cleavage of the epsilon subunit was rapid and yield of cross-linking of beta to epsilon subunit low, whether trypsin cleavage was conducted in ATP + EDTA or ATP + Mg2+. When enzyme was reacted with DCCD in ATP + Mg2+, cleavage of the epsilon subunit was slow and yield of cross-linking of beta to epsilon high, under all nucleotide conditions for proteolysis.(ABSTRACT TRUNCATED AT 250 WORDS)

Catalytic site nucleotide and inorganic phosphate dependence of the conformation of the epsilon subunit in Escherichia coli adenosinetriphosphatase

The rate of trypsin cleavage of the epsilon subunit of Escherichia coli F1 (ECF1) has been found to be ligand-dependent, as measured indirectly by the activation of the enzyme that occurs on protease digestion, or when followed directly by monitoring the cleavage of this subunit using monoclonal antibodies. The cleavage of the epsilon subunit was fast in the presence of ADP alone, ADP + MG2+, ATP + EDTA, or AMP-PNP, but slow when Pi was added along with ADP + Mg2+ or when ATP + Mg2+ was added to generate ADP + Pi (+Mg2+) in the catalytic site(s). The half-maximal concentration of Pi required in the presence of ADP + Mg2+ to protect the epsilon subunit from cleavage by trypsin was 50 microM, which is in the range measured for the high-affinity binding of Pi to F1. The ligand-dependent conformational changes in the epsilon subunit were also examined in cross-linking experiments using the water-soluble carbodiimide 1-ethyl-3-[3-(dimethylamino)propyl]carbodiimide (EDC). In the presence of ATP + Mg2+ or ADP + Mg2+ + Pi, the epsilon subunit cross-linked to beta in high yield. With ATP + EDTA or ADP + Mg2+ (no Pi), the yield of the beta-epsilon cross-linked product was much reduced. We conclude that the epsilon subunit undergoes a conformational change dependent on the presence of Pi. It has been found previously that binding of the epsilon subunit to ECF1 inhibits ATPase activity by decreasing the off rate of Pi [Dunn, S. D., Zadorozny, V. D., Tozer, R. G., & Orr, L. E. (1987) Biochemistry 26, 4488-4493]. This reciprocal relationship between Pi binding and epsilon-subunit conformation has important implications for energy transduction by the E. coli ATP synthase.

Kinetic properties of F0F1-ATPases. Theoretical predictions from alternating-site models

We present an analysis of models based on current structural concepts of the F0F1 synthases, accounting for coupling between proton transport and ATP synthesis. It is assumed that each of the three alpha beta-subunits of the synthase can exist in three different conformational states E, Eo and E*. Proton translocation is coupled to cyclic interconversion of the conformations of the alpha beta-subunits. The conformational changes of these subunits are assumed to be coordinated so that all three interconvert simultaneously, in a rate-limiting transition. Binding and release of the ligands ATP, ADP, Pi, and protons are assumed to be equilibrium steps. In one family of models, interconversion of the alpha beta-subunits of F1 is coupled to the translocation event in F0 acting as a proton carrier. In a second family of models, protons combine with F0F1 and are translocated during the interconversion step in a chemiport. Kinetic tests involving the mutual effects of [ATP], [ADP], H+', and H+" are described, allowing us to make a distinction between the different models and submodels.

Identification of a mutation in Escherichia coli F1-ATPase beta-subunit conferring resistance to aurovertin

A mutation conferring aurovertin resistance on Escherichia coli F1-ATPase was identified as R398----H in the F1 beta-subunit. Beta-subunit from the mutant does not bind aurovertin; therefore our results suggest the region of sequence around residue beta-398 is involved in aurovertin binding. Since nucleotide and aurovertin binding to isolated beta-subunit are not mutually exclusive, the data further suggest that the beta-subunit catalytic nucleotide-binding domain does not include residue 398. The mutation prevented aurovertin inhibition of ATPase at pH 6 and 8.5, implying charge on the arginine side-chain is not a major determinant of aurovertin binding or that the pK of R398 is shifted due to a peculiar environment. The equivalent residue is usually arginine in F1 beta-subunits of different species; notably in the aurovertin-insensitive thermophilic bacterium PS3 F1-ATPase, this residue is phenylalanine.

Role of energy in oxidative phosphorylation

This article reviews the current status of information regarding the role of energy in the process of oxidative phosphorylation by mitochondria. The available data suggest that in submitochondrial particles (SMP) energy is utilized for the binding of ADP and Pi and for the release of ATP bound at the catalytic sites of F1-ATPase. The process of ATP synthesis on the surface of F1 from F1-bound ADP and Pi appears to be associated with negligible free energy change. The rate of energy production by the respiratory chain modulates the kinetics of ATP synthesis between a low Km (for ADP and Pi)-low Vmax mode and a high Km-high Vmax mode. The Km extremes for ADP are 2-3 microM and 120-150 microM, and Vmax for ATP synthesis at high rates of energy production by bovine-heart SMP is about 440 S-1 (mole F1)-1 at 30 degrees C, which corresponds to 11 mumol ATP (min.mg of protein)-1. The interaction of dicyclohexylcarbodiimide (DCCD) or oligomycin at the proteolipid (subunit c) of the membrane sector (F0) of the ATP synthase complex alters the mode of ATP binding at the catalytic sites of F1, probably to one of lower affinity. It has been suggested that protonic energy might be conveyed to the catalytic sites of F1 in an analogous manner, i.e., via conformation changes in the ATP synthase complex initiated by proton-induced alterations in the structure of the DCCD-binding proteolipid. Finally, the relationship between the steady-state membrane potential (delta psi) and the rates of electron transfer and ATP synthesis has been discussed. It has been shown, in agreement with the delocalized chemiosmotic mechanism, that under appropriate conditions delta psi is exquisitely sensitive to changes in the rates of energy production and consumption.

Bacterial adenosine 5'-triphosphate synthase (F1F0): purification and reconstitution of F0 complexes and biochemical and functional characterization of their subunits

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Regulation of ATP hydrolase activity of the F0-F1 complex of rat-liver mitochondria during early hepatic regeneration

Submitochondrial particles prepared from rat liver in the early phase of hepatic regeneration possess a reduced F1 content with respect to F0 in intact F0F1-H+-ATPase complexes. Analysis of ATP hydrolysis showed a significant difference in both ESMP and isolated F1 with regard to the higher affinity Km values (Km,1) obtained from Eadie-Hofstee plots. Both ESMP and F1 from regenerating rat liver showed much lower apparent Km,1 values (0.04 and 0.03 mM, respectively) than the corresponding controls (0.08 mM for both ESMP and F1). Data presented here show that the residual F1 moieties have an altered kinetic pattern with regard to the competitive inhibitor adenosine 5'-[beta,gamma-imido]triphosphate (K1 ESMP from regenerating rat liver = 0.67 microM, K1 ESMP from control rat liver = 2.03 microM). This difference in affinity for [beta,gamma-imido]-ATP is also seen in isolated F1 (K1 regenerating rat liver = 0.04 microM, K1 control rat liver = 0.22 microM). These data indicate that during the disruptive retrodifferential phase of hepatic regeneration, changes at the level of surviving F1 sectors of the F0-F1 ATPase may play a physiological role in preventing ATP hydrolysis in vivo in the brief period of low delta microH+, induced by the presence of non-F1-associated F0 proton-conducting pathways.

Kinetics of ATP hydrolysis catalyzed by isolated TF1 and reconstituted TF0F1 ATPase

The rate of ATP hydrolysis catalyzed by isolated TF1 and reconstituted TF0F1 was measured as a function of the ATP concentration in the presence of inhibitors [ADP, Pi and 3'-O-(1-naphthoyl)ATP]. ATP hydrolysis can be described by Michaelis-Menten kinetics with Km(TF1) = 390 microM and Km (TF0F1) = 180 microM. The inhibition constants are for ADP Ki(TF1) = 20 microM and Ki(TF0F1) = 100 microM, for 3'-O-(1-naphthoyl)ATP Ki(TF1) = 150 microM and Ki(TF0F1) = 3 microM, and for Pi Ki(TF1) = 60 mM. From these results it is concluded that upon binding of TF0 to TF1 the mechanism of ATP hydrolysis catalyzed by TF1 is not changed qualitatively; however, the kinetic constants differ quantitatively.