Inhibitors of the ATP synthethase system

Cell surface adenylate kinase activity regulates the F(1)-ATPase/P2Y (13)-mediated HDL endocytosis pathway on human hepatocytes

We have previously demonstrated on human hepatocytes that apolipoprotein A-I binding to an ecto-F(1)-ATPase stimulates the production of extracellular ADP that activates a P2Y(13)-mediated high-density lipoprotein (HDL) endocytosis pathway. Therefore, we investigated the mechanisms controlling the extracellular ATP/ADP level in hepatic cell lines and primary cultures to determine their impact on HDL endocytosis. Here we show that addition of ADP to the cell culture medium induced extracellular ATP production that was due to adenylate kinase [see text] and nucleoside diphosphokinase [see text] activities, but not to ATP synthase activity. We further observed that in vitro modulation of both ecto-NDPK and AK activities could regulate the ADP-dependent HDL endocytosis. But interestingly, only AK appeared to naturally participate in the pathway by consuming the ADP generated by the ecto-F(1)-ATPase. Thus controlling the extracellular ADP level is a potential target for reverse cholesterol transport regulation.

N-WASP inhibitor wiskostatin nonselectively perturbs membrane transport by decreasing cellular ATP levels

Wiskott-Aldrich syndrome protein (WASP) and WAVE stimulate actin-related protein (Arp)2/3-mediated actin polymerization, leading to diverse downstream effects, including the formation and remodeling of cell surface protrusions, modulation of cell migration, and intracytoplasmic propulsion of organelles and pathogens. Selective inhibitors of individual Arp2/3 activators would enable more exact dissection of WASP- and WAVE-dependent cellular pathways and are potential therapeutic targets for viral pathogenesis. Wiskostatin is a recently described chemical inhibitor that selectively inhibits neuronal WASP (N-WASP)-mediated actin polymerization in vitro. A growing number of recent studies have utilized this drug in vivo to uncover novel cellular functions for N-WASP; however, the selectivity of wiskostatin in intact cells has not been carefully explored. In our studies with this drug, we observed rapid and dose-dependent inhibition of N-WASP-dependent membrane trafficking steps. Additionally, however, we found that addition of wiskostatin inhibited numerous other cellular functions that are not believed to be N-WASP dependent. Further studies revealed that wiskostatin treatment caused a rapid, profound, and irreversible decrease in cellular ATP levels, consistent with its global effects on cell function. Our data caution against the use of this drug as a selective perturbant of N-WASP-dependent actin dynamics in vivo.

Cruentaren, a New Antifungal Salicylate-Type Macrolide from Byssovorax cruenta (Myxobacteria) with Inhibitory Effect on Mitochondrial ATPase Activity

The novel macrolide cruentaren A was produced at levels up to 3.2 mg/liter by cultures of the myxobacterium Byssovorax cruenta. The new compound strongly inhibited the growth of yeasts and filamentous fungi and showed high cytotoxicity against L929 mouse fibroblast cells. A minor co-metabolite of cruentaren A, named cruentaren B, and identified as a six-membered lactone isomer of cruentaren A, showed only marginal cytotoxicity and no antifungal activity. Cruentaren A inhibited F0F1 mitochondrial ATP-hydrolysis in submitochondrial particles of yeasts and beef heart.

Biochemical and molecular characterization of a Na+-translocating F1Fo-ATPase from the thermoalkaliphilic bacterium Clostridium paradoxum

Clostridium paradoxum is an anaerobic thermoalkaliphilic bacterium that grows rapidly at pH 9.8 and 56 degrees C. Under these conditions, growth is sensitive to the F-type ATP synthase inhibitor N,N'-dicyclohexylcarbodiimide (DCCD), suggesting an important role for this enzyme in the physiology of C. paradoxum. The ATP synthase was characterized at the biochemical and molecular levels. The purified enzyme (30-fold purification) displayed the typical subunit pattern for an F1Fo-ATP synthase but also included the presence of a stable oligomeric c-ring that could be dissociated by trichloroacetic acid treatment into its monomeric c subunits. The purified ATPase was stimulated by sodium ions, and sodium provided protection against inhibition by DCCD that was pH dependent. ATP synthesis in inverted membrane vesicles was driven by an artificially imposed chemical gradient of sodium ions in the presence of a transmembrane electrical potential that was sensitive to monensin. Cloning and sequencing of the atp operon revealed the presence of a sodium-binding motif in the membrane-bound c subunit (viz., Q28, E61, and S62). On the basis of these properties, the F1Fo-ATP synthase of C. paradoxum is a sodium-translocating ATPase that is used to generate an electrochemical gradient of + that could be used to drive other membrane-bound bioenergetic processes (e.g., solute transport or flagellar rotation). In support of this proposal are the low rates of ATP synthesis catalyzed by the enzyme and the lack of the C-terminal region of the epsilon subunit that has been shown to be essential for coupled ATP synthesis.

Ectoadenylate Kinase and Plasma Membrane ATP Synthase Activities of Human Vascular Endothelial Cells

Formation of ATP from ADP on the external surface of vascular endothelial cells has been attributed to plasma membrane ATP synthase, ectoadenylate kinase (ecto-AK), and/or ectonucleoside diphosphokinase. These enzymes or their catalytic products have been causatively linked to the elaboration of vascular networks and the regulation of capillary function. The amount of ATP generated extracellularly is small, requiring sensitive analytical methods for quantification. Human umbilical vein endothelial cells were used to revisit extracellular ATP synthesis using a reliable tetrazolium reduction assay and multiwell plate cultures. Test conditions compatible with AK stability were established. Extracellular AK activity was found to be <1% of the total (intracellular and extracellular), raising the possibility that the external enzyme could have leaked from living cells and/or a few dying cells. To determine whether AK inadvertently leaked from the cells, the activity of another cytoplasmic enzyme, glucose-6-phosphate dehydrogenase (G6PD), was also measured. G6PD is present in the cytoplasm in similar abundance to AK. The activity ratio of G6PD (extracellular/total) was found to be similar to that of AK. Because G6PD in the medium was probably due to leakage, other cytoplasmic macromolecules, including AK, should be released proportionately from the cells. The role of plasma membrane ATP synthase in extracellular ATP formation was examined using Hanks' balanced salt solution with and without selective inhibitors of AK and ATP synthase activities. With P(1),P(5)-di(adenosine 5')-pentaphosphate (inhibitor of AK activity), no extracellular ATP synthesis was detected, whereas with oligomycin, piceatannol, and aurovertin (inhibitors of F(1)F(0)-ATP synthase and F(1)-ATPase activities), no inhibition of extracellular ATP synthesis was observed. AK activity alone could account for the observed extracellular ATP synthesis. The possible impact of ADP impurity in the assays is discussed.

Aurovertin E, a new polyene pyrone from the basidiomycete Albatrellus confluens

A new polyene pyrone, aurovertin E (2), was isolated along with aurovertin B (1) from the culture mycelia of the basidiomycete Albatrellus confluens. Their structures were elucidated on the basis of spectroscopic studies including 2D NMR experiments. This is the first example of the occurrence of aurovertins in basidiomycetes.

Human keratinocytes release ATP and utilize three mechanisms for nucleotide interconversion at the cell surface

Nucleotide activation of P2 receptors is important in autocrine and paracrine regulation in many tissues. In the epidermis, nucleotides are involved in proliferation, differentiation, and apoptosis. In this study, we have used a combination of luciferin-luciferase luminometry, pharmacological inhibitors, and confocal microscopy to demonstrate that HaCaT keratinocytes release ATP into the culture medium, and that there are three mechanisms for nucleotide interconversion, resulting in ATP generation at the cell surface. Addition of ADP, GTP, or UTP to culture medium elevated the ATP concentration. ADP to ATP conversion was inhibited by diadenosine pentaphosphate, oligomycin, and UDP, suggesting the involvement of cell surface adenylate kinase, F(1)F(0) ATP synthase, and nucleoside diphosphokinase (NDPK), respectively, which was supported by immunohistochemistry. Simultaneous addition of ADP and GTP elevated ATP above that for each nucleotide alone indicating that GTP acts as a phosphate donor. However, the activity of NDPK, F(1)F(0) ATP synthase or the forward reaction of adenylate kinase could not fully account for the culture medium ATP content. We postulate that this discrepancy is due to the reverse reaction of adenylate kinase utilizing AMP. In normal human skin, F(1)F(0) ATP synthase and NDPK were differentially localized, with mitochondrial expression in the basal layer, and cell surface expression in the differentiated layers. We and others have previously demonstrated that keratinocytes express multiple P2 receptors. In this study we now identify the potential sources of extracellular ATP required to activate these receptors and provide better understanding of the role of nucleotides in normal epidermal homeostasis and wound healing.

Proton slip in the ATP synthase of Rhodobacter capsulatus: induction, proton conduction, and nucleotide dependence

FOF1-ATP synthase converts two energetic "currencies" of the cell (ATP and protonmotive force, pmf) by coupling two rotary motors/generators. Their coupling efficiency is usually very high. Uncoupled proton leakage (slip) has only been observed in chloroplast enzyme at unphysiologically low nucleotide concentration. We investigated the properties of proton slip in chromatophores (sub-bacterial vesicles) from Rhodobacter capsulatus in the single-enzyme-per-vesicle mode. The membrane was energized by excitation with flashing light and the relaxation of the transmembrane voltage and pH difference was photometrically detected. We found that: (1) Proton slip occurred only at low nucleotide concentration (<1 microM) and after pre-illumination over several seconds. (2) Slip induction by pmf was accompanied by the release of approximately 0.25 mol ADP per mole of enzyme. There was no detectable detachment of F1 from FO. (3) The transmembrane voltage and the pH difference were both efficient in slip induction. Once induced, slip persisted for hours, and was only partially reverted by the addition of ADP or ATP (>1 microM). (4) There was no pmf threshold for the proton transfer through the slipping enzyme; slip could be driven both by voltage and pH difference. (5) The conduction was ohmic and weakly pH-dependent in the range from 5.5 to 9.5. The rate constant of proton transfer under slip conditions was 185 s(-1) at pH 8. Proton slip probably presents the free-wheeling of the central rotary shaft, subunit gamma, in an open structure of the (alphabeta)3 hexagon with no nucleotides in the catalytic sites.

The ion channel of F-ATP synthase is the target of toxic organotin compounds

ATP is the universal energy currency of living cells, and the majority of it is synthesized by the F1F0 ATP synthase. Inhibitors of this enzyme are therefore potentially detrimental for all life forms. Tributyltin chloride (TBT-Cl) inhibits ATP hydrolysis by the Na(+)-translocating ATP synthase of Ilyobacter tartaricus or the H(+)-translocating counterpart of Escherichia coli with apparent Ki of 200 nM. To target the site of this inhibition, we synthesized a tritium-labeled derivative of TBT-Cl in which one of the butyl groups was replaced by a photoactivatable aryldiazirine residue. Upon illumination, subunit a of the ATP synthase becomes specifically modified, and this labeling is suppressed in the presence of the original inhibitor. In case of the Na+ ATP synthase, labeling is also suppressed in the presence of Na+ ions, suggesting an interference in Na+ or TBT-Cl binding to subunit a. This interference is corroborated by the protection of ATP hydrolysis from TBT-Cl inhibition by 105 mM Na+. TBT-Cl strongly inhibits Na+ exchange by the reconstituted I. tartaricus ATP synthase. Taken together these results indicate that the subunit a ion channel is the target site for ATPase inhibition by toxic organotin compounds. An inhibitor interacting specifically with this site has not been reported previously.

The proton-driven rotor of ATP synthase: ohmic conductance (10 fS), and absence of voltage gating

The membrane portion of F(0)F(1)-ATP synthase, F(0), translocates protons by a rotary mechanism. Proton conduction by F(0) was studied in chromatophores of the photosynthetic bacterium Rhodobacter capsulatus. The discharge of a light-induced voltage jump was monitored by electrochromic absorption transients to yield the unitary conductance of F(0). The current-voltage relationship of F(0) was linear from 7 to 70 mV. The current was extremely proton-specific (>10(7)) and varied only slightly ( approximately threefold) from pH 6 to 10. The maximum conductance was approximately 10 fS at pH 8, equivalent to 6240 H(+) s(-1) at 100-mV driving force, which is an order-of-magnitude greater than of coupled F(0)F(1). There was no voltage-gating of F(0) even at low voltage, and proton translocation could be driven by deltapH alone, without voltage. The reported voltage gating in F(0)F(1) is thus attributable to the interaction of F(0) with F(1) but not to F(0) proper. We simulated proton conduction by a minimal rotary model including the rotating c-ring and two relay groups mediating proton exchange between the ring and the respective membrane surface. The data fit attributed pK values of approximately 6 and approximately 10 to these relays, and placed them close to the membrane/electrolyte interface.

Rhodamine 123 as a probe of mitochondrial membrane potential: evaluation of proton flux through F0 during ATP synthesis

Rhodamine 123 (RH-123) was used to monitor the membrane potential of mitochondria isolated from rat liver. Mitochondrial energization induces quenching of RH-123 fluorescence and the rate of fluorescence decay is proportional to the mitochondrial membrane potential. Exploiting the kinetics of RH-123 fluorescence quenching in the presence of succinate and ADP, when protons are both pumped out of the matrix driven by the respiratory chain complexes and allowed to diffuse back into the matrix through ATP synthase during ATP synthesis, we could obtain an overall quenching rate proportional to the steady-state membrane potential under state 3 condition. We measured the kinetics of fluorescence quenching by adding succinate and ADP in the absence and presence of oligomycin, which abolishes the ADP-driven potential decrease due to the back-flow of protons through the ATP synthase channel, F(0). As expected, the initial rate of quenching was significantly increased in the presence of oligomycin, and conversely preincubation with subsaturating concentrations of the uncoupler carbonyl cyanide p-trifluoro-metoxyphenilhydrazone (FCCP) induced a decreased rate of quenching. N,N'-dicyclohexylcarbodiimide (DCCD) behaved similarly to oligomycin in increasing the rate of quenching. These findings indicate that RH-123 fluorescence quenching kinetics give reliable and sensitive evaluation of mitochondrial membrane potential, complementing steady-state fluorescence measurements, and provide a mean to study proton flow from the mitochondrial intermembrane space to the matrix through the F(0) channel.

Total synthesis of (+)-asteltoxin

A convergent synthesis of (+)-asteltoxin (1) has been achieved by the Horner-Emmons olefination of bis(tetrahydrofuran) aldehyde 53 and alpha-pyrone phosphonate 5. A key step features the stereoselective construction of a sterically congested quaternary center embedded in the densely functionalized bis(tetrahydrofuran) subunit by a Lewis acid-catalyzed, pinacol-type rearrangement of an epoxy silyl ether. This pivotal rearrangement methodology parallels the proposed biosynthetic pathway of 1 and is ripe for applications to the stereocontrolled synthesis of structurally complex natural products.

Control analysis of mitochondrial metabolism in intact hepatocytes: effect of interleukin-1beta and interleukin-6

Interleukin-1beta (IL-1beta) and interleukin-6 (IL-6) are produced by hepatic nonparenchymal cells after systemic injury and have been reported to inhibit ATP synthesis in hepatocytes, which may contribute to hepatic dysfunction in inflammatory states. To elucidate the mechanisms of action of IL-1beta and IL-6 on hepatocellular ATP synthesis, we measured the oxygen uptake rate (OUR) and mitochondrial membrane potential (MMP) of stable hepatocyte cultures, and analyzed the dynamic MMP response following the addition of mitochondrial inhibitors (antimycin A and oligomycin) with a model of mitochondrial metabolism. IL-1beta reduced mitochondrial OUR coupled to ATP synthesis via inhibition of phosphorylation reactions which dissipate the MMP, including ATP synthesis and consumption. Furthermore, the ATP synthesis rate in cytokine-free and IL-1beta-treated hepatocytes was controlled primarily by phosphorylation reactions, which corresponds to a state where the ATP synthesis rate closely follows the cellular energy demand. Thus, IL-1beta-mediated effects on electron transport and substrate oxidation reactions are not likely to significantly impact on ATP synthesis. IL-6 did not reduce mitochondrial OUR coupled to ATP synthesis, but shifted the control for ATP synthesis towards processes which generate the MMP, indicating that IL-6 induces a metabolic state where cellular functions are limited by the mitochondrial energy supply.

Chromatophore vesicles of Rhodobacter capsulatus contain on average one F(O)F(1)-ATP synthase each

ATP synthase is a unique rotary machine that uses the transmembrane electrochemical potential difference of proton (Delta(H(+))) to synthesize ATP from ADP and inorganic phosphate. Charge translocation by the enzyme can be most conveniently followed in chromatophores of phototrophic bacteria (vesicles derived from invaginations of the cytoplasmic membrane). Excitation of chromatophores by a short flash of light generates a step of the proton-motive force, and the charge transfer, which is coupled to ATP synthesis, can be spectrophotometrically monitored by electrochromic absorption transients of intrinsic carotenoids in the coupling membrane. We assessed the average number of functional enzyme molecules per chromatophore vesicle. Kinetic analysis of the electrochromic transients plus/minus specific ATP synthase inhibitors (efrapeptin and venturicidin) showed that the extent of the enzyme-related proton transfer dropped as a function of the inhibitor concentration, whereas the time constant of the proton transfer changed only marginally. Statistical analysis of the kinetic data revealed that the average number of proton-conducting F(O)F(1)-molecules per chromatophore was approximately one. Thereby chromatophores of Rhodobacter capsulatus provide a system where the coupling of proton transfer to ATP synthesis can be studied in a single enzyme/single vesicle mode.

Coupling of proton flow to ATP synthesis in Rhodobacter capsulatus: F(0)F(1)-ATP synthase is absent from about half of chromatophores

F(0)F(1)-ATP synthase (H(+)-ATP synthase, F(0)F(1)) utilizes the transmembrane protonmotive force to catalyze the formation of ATP from ADP and inorganic phosphate (P(i)). Structurally the enzyme consists of a membrane-embedded proton-translocating F(0) portion and a protruding hydrophilic F(1) part that catalyzes the synthesis of ATP. In photosynthetic purple bacteria a single turnover of the photosynthetic reaction centers (driven by a short saturating flash of light) generates protonmotive force that is sufficiently large to drive ATP synthesis. Using isolated chromatophore vesicles of Rhodobacter capsulatus, we monitored the flash induced ATP synthesis (by chemoluminescence of luciferin/luciferase) in parallel to the transmembrane charge transfer through F(0)F(1) (by following the decay of electrochromic bandshifts of intrinsic carotenoids). With the help of specific inhibitors of F(1) (efrapeptin) and of F(0) (venturicidin), we decomposed the kinetics of the total proton flow through F(0)F(1) into (i) those coupled to the ATP synthesis and (ii) the de-coupled proton escape through F(0). Taking the coupled proton flow, we calculated the H(+)/ATP ratio; it was found to be 3.3+/-0.6 at a large driving force (after one saturating flash of light) but to increase up to 5.1+/-0.9 at a smaller driving force (after a half-saturating flash). From the results obtained, we conclude that our routine chromatophore preparations contained three subsets of chromatophore vesicles. Chromatophores with coupled F(0)F(1) dominated in fresh material. Freezing/thawing or pre-illumination in the absence of ADP and P(i) led to an increase in the fraction of chromatophores with at least one de-coupled F(0)(F(1)). The disclosed fraction of chromatophores that lacked proton-conducting F(0)(F(1)) (approx. 40% of the total amount) remained constant upon these treatments.

Effects of efrapeptin and destruxin, metabolites of entomogenous fungi, on the hydrolytic activity of a vacuolar type ATPase identified on the brush border membrane vesicles of Galleria mellonella midgut and on plant membrane bound hydrolytic enzymes

The brush border membrane of the insect midgut is an initial site for interaction of insecticidal proteins. We have investigated the possibility that it may contain a target site for two insecticidal fungal toxins, destruxin and efrapeptin, both of which are ATPase inhibitors. We have studied the effects of the toxins on the hydrolytic activity of a vacuolar type ATPase (V-ATPase) that we have identified from Galleria mellonella midgut columnar cell brush border membrane vesicles (BBMV) by its cation and pH dependence, sensitivity to proton pump inhibitors and K(m) (0.49 mM ATP). Efrapeptin strongly inhibited the BBMV V-ATPase but destruxin had little effect. We compared the effects of the inhibitors on known plant membrane hydrolytic enzymes, and although the vacuolar pyrophosphatase and plasma membrane ATPase were not inhibited by the toxins, the V-ATPase from mung bean, but not barley, was inhibited (50%) by 10 microM concentrations of both compounds. Different forms of the toxins were tested on the ATPases and destruxin B and efrapeptin F were the most effective. Kinetic analysis showed that the purified forms of both compounds inhibited the V-ATPases uncompetitively and modelling of data for inhibition of the BBMV V-ATPase by efrapeptin at concentrations of 0.06--12 microM yielded a K(i) of 0.125 microM.

Antimalarial activities of peptide antibiotics isolated from fungi

Malaria caused by Plasmodium falciparum is a major public health problem in the developing countries of the world. Clinical treatment of malaria has become complicated due to the occurrence of infections caused by drug resistant parasites. Secondary metabolites from fungi are an attractive source of chemotherapeutic agents. This work reports the isolation and in vitro antiplasmodial activities of peptide antibiotics of fungal origin. The three peptide antibiotics used in this study were efrapeptins, zervamicins, and antiamoebin. The high-performance liquid chromatography-purified peptides were characterized by nuclear magnetic resonance and mass spectral analysis. All three fungal peptides kill P. falciparum in culture with 50% inhibitory concentrations in the micromolar range. A possible mode of action of these peptide antibiotics on P. falciparum is presented.

Fusion of chromatophores from photosynthetic bacteria with a supported lipid layer: characterization of the electric units

Direct electrometric measurements of membrane potential changes are a valuable tool for study of vectorial transfer of electrons, protons, and ions. Commonly model membrane systems are created by fusion of lipid/protein vesicles with lipid-coated thin films. We characterized the electric units resulting from this process using chromatophores from the purple bacterium Rhodobacter sphaeroides and either a Mylar film or a planar modified gold electrode as support. Investigation of the shunting activity of the ionophore gramicidin on the flash-induced potential change demonstrates fusion of individual chromatophores to form independent 'blisters', which preserve an interior aqueous compartment. Under current-clamp conditions the photovoltage follows the change of the membrane potential of the individual blisters.

Simultaneous measurement of deltapH and electron transport in chloroplast thylakoids by 9-aminoacridine fluorescence

Electron transport and the electrochemical proton gradient across the thylakoid membrane are two fundamental parameters of photosynthesis. A combination of the electron acceptor, ferricyanide and the DeltapH indicator, 9-aminoacridine, was used to measure simultaneously electron transport rates and DeltapH solely by changes in the fluorescence of 9-aminoacridine. This method yields values for the rate of electron transport that are comparable with those obtained by established methods. Using this method a relationship between the rate of electron transport and DeltapH at various uncoupler concentrations or light intensities was obtained. In addition, the method was used to study the effect of reducing the disulfide bridge in the gamma-subunit of the chloroplast ATP synthase on the relation of electron transport to DeltapH. When the ATP synthase is reduced and alkylated, the threshold DeltapH at which the ATP synthase becomes leaky to protons is lower compared with the oxidized enzyme. Proton flow through the enzyme at a lower DeltapH may be a key step in initiation of ATP synthesis in the reduced enzyme and may be the way by which reduction of the disulfide bridge in the gamma-subunit enables high rates of ATP synthesis at low DeltapH values.

Mitochondrial targets of drug toxicity

Mitochondria have long been recognized as the generators of energy for the cell. Like any other power source, however, mitochondria are highly vulnerable to inhibition or uncoupling of the energy harnessing process and run a high risk for catastrophic damage to the cell. The exquisite structural and functional characteristics of mitochondria provide a number of primary targets for xenobiotic-induced bioenergetic failure. They also provide opportunities for selective delivery of drugs to the mitochondrion. In light of the large number of natural, commercial, pharmaceutical, and environmental chemicals that manifest their toxicity by interfering with mitochondrial bioenergetics, it is important to understand the underlying mechanisms. The significance is further underscored by the recent identification of bioenergetic control points for cell replication and differentiation and the realization that mitochondria play a determinant role in cell signaling and apoptotic modes of cell death.

Inhibition of mitochondrial proton F0F1-ATPase/ATP synthase by polyphenolic phytochemicals

Mitochondrial proton F0F1-ATPase/ATP synthase synthesizes ATP during oxidative phosphorylation. In this study, we examined the effects of several groups of polyphenolic phytochemicals on the activity of the enzyme. Resveratrol, a stilbene phytoalexin that is present in grapes and red wine, concentration-dependently inhibited the enzymatic activity of both rat brain and liver F0F1-ATPase/ATP synthase (IC(50) of 12 - 28 microM). Screening of other polyphenolic phytochemicals using rat brain F0F1-ATPase activity resulted in the following ranking potency (IC(50) in parenthesis): piceatannol (8 microM)>resveratrol (19 microM)=(-)epigallocatechin gallate (17 microM)>(-)epicatechin gallate, curcumin (45 microM)>genistein=biochanin A=quercetin=kaempferol=morin (55 - 65 microM)>phloretin=apigenin=daidzein (approx. 100 microM). Genistin, quercitrin, phloridzin, (+)catechin, (+)epicatechin, (-)epicatechin and (-)epigallocatechin had little effect at similar concentrations. Tannic acid, theaflavins (tea extract) and grape seed proanthocyanidin extract (GSPE) had IC(50) values of 5, 20 and 30 microg ml(-1), respectively. Several monophenolic antioxidants and non-phenolic compounds were ineffective at concentrations of 210 microM or higher. The inhibition of F0F1-ATPase by resveratrol and genistein was non-competitive in nature. The effects of polyphenolic phytochemicals were additive. Both resveratrol and genistein had little effect on the Na(+)/K(+)-ATPase activity of porcine cerebral cortex, whereas quercetin had similar inhibitory potency as for F0F1-ATPase. In conclusion, the ATP synthase is a target for dietary phytochemicals. This pharmacological property of these phytochemicals should be included in the examination of their health benefits as well as potential cytotoxicity.

Farnesol-induced generation of reactive oxygen species dependent on mitochondrial transmembrane potential hyperpolarization mediated by F(0)F(1)-ATPase in yeast

An isoprenoid farnesol (FOH) inhibited cellular oxygen consumption and induced mitochondrial generation of reactive oxygen species (ROS) in cells of Saccharomyces cerevisiae in correlation with hyperpolarization of the mitochondrial transmembrane potential (mtDeltaPsi). The FOH-induced events were coordinately abolished with the F(1)-ATPase inhibitor sodium azide as well as the F(0)F(1)-ATPase inhibitor oligomycin, suggesting the dependence of ROS generation on mtDeltaPsi hyperpolarization mediated by the proton pumping function of F(0)F(1)-ATPase as a result of ATP hydrolysis. The role of F(1)-ATPase activity in mtDeltaPsi hyperpolarization was supported by the intracellular depletion of ATP in FOH-treated cells and its protection with sodium azide. An indirect mechanism was suggested to exist in the regulation of F(0)F(1)-ATPase by FOH to accelerate its ATP-hydrolyzing activity.

Piceatannol, a stilbene phytochemical, inhibits mitochondrial F0F1-ATPase activity by targeting the F1 complex

Piceatannol is a stilbene phytochemical from the seeds of Euphorbia lagascae, previously identified as an antileukemic principle. Piceatannol is considered an inhibitor of several tyrosine kinases. We recently reported that resveratrol, another stilbene phytoalexin from grape seeds, was an inhibitor of ATP synthase. Here, we demonstrated that piceatannol potently inhibited the rat brain mitochondrial F0F1-ATPase activity in both solubilized and submitochondrial preparations (IC50 of 8-9 microM), while having relatively small effect on the Na(+), K(+)-ATPase activity of porcine cerebral cortex (no effect up to 7 microM). Piceatannol inhibited the ATPase activity of the purified rat liver F1 with IC50 of about 4 microM, while resveratrol was slightly less active (IC50 of about 14 microM). Our results indicate that piceatannol and resveratrol inhibit the F-type ATPase by targeting the F1 sector, which is located to the inner membrane of mitochondria and plasma membrane of normal endothelial cells and several cancer cell lines. This mechanism could potentially contribute to the multiple effects of these chemopreventive phytochemicals.

ATP-synthase of Rhodobacter capsulatus: coupling of proton flow through F0 to reactions in F1 under the ATP synthesis and slip conditions

A stepwise increasing membrane potential was generated in chromatophores of the phototrophic bacterium Rhodobacter capsulatus by illumination with short flashes of light. Proton transfer through ATP-synthase (measured by electrochromic carotenoid bandshift and by pH-indicators) and ATP release (measured by luminescence of luciferin-luciferase) were monitored. The ratio between the amount of protons translocated by F0F1 and the ATP yield decreased with the flash number from an apparent value of 13 after the first flash to about 5 when averaged over three flashes. In the absence of ADP, protons slipped through F0F1. The proton transfer through F0F1 after the first flash contained two kinetic components, of about 6 ms and 20 ms both under the ATP synthesis conditions and under slip. The slower component of proton transfer was substantially suppressed in the absence of ADP. We attribute our observations to the mechanism of energy storage in the ATP-synthase needed to couple the transfer of four protons with the synthesis of one molecule of ATP. Most probably, the transfer of initial protons of each tetrad creates a strain in the enzyme that slows the translocation of the following protons.

Rapid inhibition of rat brain mitochondrial proton F0F1-ATPase activity by estrogens: comparison with Na+, K+ -ATPase of porcine cortex

Our earlier studies have identified oligomycin sensitivity-conferring protein (OSCP), a subunit of proton F0F1-ATPase/ATP synthase in the mitochondrial inner membranes, as a new estradiol binding protein. This finding suggests that mitochondrial ATPase/ATP synthase could be a potential target for estradiol or compounds with similar structures. Here, we report that estradiol and several other compounds inhibited F0F1-ATPase activity of detergent-solubilized rat brain mitochondrial preparations in a following decreasing order: diethylstilbestrol (half-inhibition concentration, IC50 of 10-25 microM) > alpha-zearalenol, 4-hydroxyestradiol (1C50 of 55 microM) >2-hydroxyestradiol (IC50 of 110 microM), 17beta-estradiol, 17alpha-estradiol > beta-zearalanol > estriol, testosterone, 16alpha-hydroxyestrone > corticosterone, progesterone, dehydroepiandrosterone, dehydroepiandrosterone 3-sulfate, cholesterol (less than 10% inhibition at 140 microM). On the other hand, Na+, K+ -ATPase of porcine cortex showed different sensitivity to the compounds tested above. At 70 microM, the rank of inhibitory potency in decreasing order was as follows: 2-hydroxyestradiol (IC50 of 70 microM) > diethylstilbestrol> 4-hydroxyestradiol > progesterone > alpha-zearalenol, while other compounds had little effect (less than 5%). The data indicate that the ubiquitous mitochondrial F0F1-ATPase is a specific target site for estradiol and related estrogenic compounds; however, under this in vitro condition, the effect seems to require pharmacological concentrations.

Presence of two enzymes, different from the F1F0-ATPase, hydrolyzing nucleotides in human term placental mitochondria

The hydrolysis of ATP, ADP or GTP was characterized in mitochondria and submitochondrial particles since a tightly-bound ATPase associated with the inner mitochondrial membrane from the human placenta has been described. Submitochondrial particles, which are basically inner membranes, were used to define the location of this enzyme. Mitochondria treated with trypsin and specific inhibitors were also used. The oxygen consumption stimulated by ATP or ADP was 100% inhibited in intact mitochondria by low concentrations of oligomycin (0.5 microgram/mg) or venturicidine (0.1 microgram/mg), while the hydrolysis of ATP or ADP was insensitive to higher concentrations of these inhibitors but it was inhibited by vanadate. Oligomycin or venturicidine showed a different inhibition pattern in intact mitochondria in relation to the hydrolysis of ATP, ADP or GTP. When submitochondrial particles were isolated from mitochondria incubated with oligomycin or venturicidine, no further inhibition of the nucleotide hydrolysis was observed, contrasting with the partial inhibition observed in the control. By incubating the placental mitochondria with trypsin, a large fraction of the hydrolysis of nucleotides was eliminated. In submitochondrial particles obtained from mitochondria treated with trypsin or trypsin plus oligomycin, the hydrolysis of ATP was 100% sensitive to oligomycin at low concentrations, resembling the oxygen consumption; however, this preparation still showed some ADP hydrolysis. Native gel electrophoresis showed two bands hydrolyzing ADP, suggesting at least two enzymes involved in the hydrolysis of nucleotides, besides the F1F0-ATPase. It is concluded that human placental mitochondria possesses ADPase and ATP-diphosphohydrolase activities (247).

Effects of the inhibitors azide, dicyclohexylcarbodiimide, and aurovertin on nucleotide binding to the three F1-ATPase catalytic sites measured using specific tryptophan probes

Equilibrium nucleotide binding to the three catalytic sites of Escherichia coli F1-ATPase was measured in the presence of the inhibitors azide, dicyclohexylcarbodiimide, and aurovertin to elucidate mechanisms of inhibition. Fluorescence signals of beta-Trp-331 and beta-Trp-148 substituted in catalytic sites were used to determine nucleotide binding parameters. Azide brought about small decreases in Kd(MgATP) and Kd(MgADP). Notably, under MgATP hydrolysis conditions, it caused all enzyme molecules to assume a state with three catalytic site-bound MgATP and zero bound MgADP. These results rule out the idea that azide inhibits by "trapping" MgADP. Rather, azide blocks the step at which signal transmission between catalytic sites promotes multisite hydrolysis. Aurovertin bound with stoichiometry of 1.8 (mol/mol of F1) and allowed significant residual turnover. Cycling of the aurovertin-free beta-subunit catalytic site through three normal conformations was indicated by MgATP binding data. Aurovertin did not change the normal ratio of 1 bound MgATP/2 bound MgADP in catalytic sites. The results indicate that it acts to slow the switch of catalytic site affinities ("binding change step") subsequent to MgATP hydrolysis. Dicyclohexylcarbodiimide shifted the ratio of catalytic site-bound MgATP/MgADP from 1:2 to 1.6:1.4, without affecting Kd(MgATP) values. Like azide, it also appears to affect activity at the step after MgATP binding, in which signal transmission between catalytic sites promotes MgATP hydrolysis.

Functional F1-ATPase essential in maintaining growth and membrane potential of human mitochondrial DNA-depleted rho degrees cells

F1-ATPase assembly has been studied in human rho degrees cells devoid of mitochondrial DNA (mtDNA). Since, in these cells, oxidative phosphorylation cannot provide ATP, their growth relies on glycolysis. Despite the absence of the mtDNA-coded F0 subunits 6 and 8, rho degrees cells possessed normal levels of F1-ATPase alpha and beta subunits. This F1-ATPase was functional and azide- or aurovertin-sensitive but oligomycin-insensitive. In addition, aurovertin decreased cell growth in rho degrees cells and also reduced their mitochondrial membrane potential, as measured by rhodamine 123 fluorescence. Therefore, a functional F1-ATPase was important to maintain the mitochondrial membrane potential and the growth of these rho degrees cells. Bongkrekic acid, a specific adenine nucleotide translocator (ANT) inhibitor, also reduced rho degrees cell growth and mitochondrial membrane potential. In conclusion, rho degrees cells need both a functional F1-ATPase and a functional ANT to maintain their mitochondrial membrane potential, which is necessary for their growth. ATP hydrolysis catalyzed by F1 must provide ADP3- at a sufficient rate to maintain a rapid exchange with the glycolytic ATP4- by ANT, this electrogenic exchange inducing a mitochondrial membrane potential efficient enough to sustain cell growth. However, since the effects of bongkrekic acid and of aurovertin were additive, other electrogenic pumps should cooperate with this pathway.

Modulation of mitochondrial electrical potential: a candidate mechanism for drug resistance in African trypanosomes

Bloodstream forms of four populations of the livestock pathogen Trypanosoma congolense, isolated from different natural infections, have been shown to exhibit a wide range of sensitivities to the trypanocide isometamidium chloride (Samorin(R)). In mice the 50% curative doses (CD50) for Samorin range from 0.007 to 20 mg/kg body weight. Uptake of isometamidium chloride demonstrated Michaelis-Menten-type kinetics in all the populations, with Km values in the range 0.35-0.87 microM, and Vmax varied from 17 to 216 pmol/min per 10(8) cells. The magnitude of Vmax was correlated with sensitivity to the drug. In contrast, no correlation was observed between Km values and drug sensitivity. Pulse-chase experiments indicated two compartments for accumulation of drug. The first consists of freely diffusible drug that is invariant between populations; the other consists of retained isometamidium, which is of variable magnitude between the populations and is correlated with drug sensitivity. Autoradiography and fluorescence microscopy demonstrated initial, rapid accumulation of the drug within the mitochondrion, specifically the kinetoplast. In a drug-sensitive population of T. congolense, agents affecting mitochondrial function were shown to produce dose-dependent inhibition of mitochondrial membrane potential (DeltaPsimito), as measured by the accumulation of the lipophilic cations [3H]methyltriphenylphosphonium iodide or rhodamine 123. The agents also produced parallel inhibition of isometamidium uptake, suggesting an involvement of DeltaPsimito in the accumulation of the drug. When characterized in each of the four populations, the spontaneous DeltaPsimito was shown to be characteristic of each population and was correlated with Vmax for drug uptake and sensitivity to the drug in vitro and in vivo. We therefore conclude that in T. congolense DeltaPsimito is an important determinant of the rate and accumulation of the trypanocide isometamidium chloride. Populations of this trypanosome species vary with respect to DeltaPsimito, which is correlated with sensitivity to isometamidium. We suggest that when exposed to drug, the selection of such populations represents a novel mechanism of drug resistance in protozoan parasites.

Identification of proteolipid from an extremely halophilic archaeon Halobacterium salinarum as an N,N'-dicyclohexyl-carbodiimide binding subunit of ATP synthase

ATP synthesis in an extremely halophilic archaeon, Halobacterium salinarum, was inhibited by N-cyclohexyl-N'-[4-(dimethylamino)-alpha-naphthyl]carbodiimide (NCD-4), a fluorescent analog of N,N'-dicyclohexylcarbodiimide (DCCD). By tracing the fluorescent signal, a hydrophobic 8-kDa protein (proteolipid) was purified from the halobacterial membrane as one of the most DCCD-reactive proteins and its N-terminal amino acid sequence was determined. The gene encoding the proteolipid was found in the region upstream of the genes encoding the two major subunits of halobacterial A-type ATPase [K. Ihara and Y.Mukohata (1991) Arch. Biochem. Biophys. 286, 111-116]. Halobacterial proteolipid was more similar in size to the proteolipid of F-type ATPase than that of V-type ATPase. However, multiple amino acid sequence alignment of proteolipids showed a higher degree of relatedness between V-type and A-type ATPase proteolipids. Together with the recent finding of a triplicate proteolipid encoding gene from the methanogenic archaeon Methanococcus jannaschii [C. J. Bult et al. (1996) Science 273, 1058-1073], proteolipids from archaea seem to have diverse characteristics in comparison with those from eubacteria or from eukaryotes.

The structure of bovine F1-ATPase complexed with the peptide antibiotic efrapeptin

In the previously determined structure of mitochondrial F1-ATPase determined with crystals grown in the presence of adenylyl-imidodiphosphate (AMP-PNP) and ADP, the three catalytic beta-subunits have different conformations and nucleotide occupancies. AMP-PNP and ADP are bound to subunits beta TP and beta DP, respectively, and the third beta-subunit (beta E) has no bound nucleotide. The efrapeptins are a closely related family of modified linear peptides containing 15 amino acids that inhibit both ATP synthesis and hydrolysis by binding to the F1 catalytic domain of F1F0-ATP synthase. In crystals of F1-ATPase grown in the presence of both nucleotides and inhibitor, efrapeptin is bound to a unique site in the central cavity of the enzyme. Its binding is associated with small structural changes in side chains of F1-ATPase around the binding pocket. Efrapeptin makes hydrophobic contacts with the alpha-helical structure in the gamma-subunit, which traverses the cavity, and with subunit beta E and the two adjacent alpha-subunits. Two intermolecular hydrogen bonds could also form. Intramolecular hydrogen bonds probably help to stabilize efrapeptin's two domains (residues 1-6 and 9-15, respectively), which are connected by a flexible region (beta Ala-7 and Gly-8). Efrapeptin appears to inhibit F1-ATPase by blocking the conversion of subunit beta E to a nucleotide binding conformation, as would be required by an enzyme mechanism involving cyclic interconversion of catalytic sites.

DCCD-sensitive proton permeability of bacterial photosynthetic membranes. Cross-reconstitution studies with purified bovine heart Fo subunits

The DCCD-sensitive proton permeability of chromatophores, from a green strain of Rhodobacter Capsulatus is potentiometrically detected following the proton release induced by a transmembrane diffusion potential imposed by a valinomycin-mediated potassium influx with a procedure already used for bovine heart submitochondrial particles (ESMP) and vesicles from Escherichia coli (Zanotti et al. (1994) Eur. J. Biochem. 222, 733-741). In the photosynthetic system, addition of increasing amounts of DCCD inhibits, with a similar titre, both proton permeability and MgATP-dependent ATPase activity as detected in the dark. The titre for 50% inhibition coincides with that obtained measuring proton permeability and ATP hydrolysis in ESMP. Upon removal of F1, the passive proton permeability is much less sensitive to DCCD in chromatophores than in USMP, suggesting that in chromatophores the F1-Fo interaction shapes the DCCD-sensitive proton conducting pathway. Addition of the purified mitochondrial FoI-PVP and oligomycin sensitivity-conferring (OSCP) proteins to the F1 stripped chromatophores restored the sensitivity of proton permeability to DCCD detected in untreated chromatophores. Analysis of the binding of 14C[DCCD] on F1 stripped chromatophores shows that the increase of DCCD sensitivity of proton permeability, caused by addition of mitochondrial Fo proteins, is related to an increase of the binding of the inhibitor to subunit c of Fo sector of ATP synthase complex.

The structure of bovine F1-ATPase complexed with the antibiotic inhibitor aurovertin B

In the structure of bovine mitochondrial F1-ATPase that was previously determined with crystals grown in the presence of adenylyl-imidodiphosphate (AMP-PNP) and ADP, the three catalytic beta-subunits have different conformations and nucleotide occupancies. Adenylyl-imidodiphosphate is bound to one beta-subunit (betaTP), ADP is bound to the second (betaDP), and no nucleotide is bound to the third (betaE). Here we show that the uncompetitive inhibitor aurovertin B binds to bovine F1 at two equivalent sites in betaTP and betaE, in a cleft between the nucleotide binding and C-terminal domains. In betaDP, the aurovertin B pocket is incomplete and is inaccessible to the inhibitor. The aurovertin B bound to betaTP interacts with alpha-Glu399 in the adjacent alphaTP subunit, whereas the aurovertin B bound to betaE is too distant from alphaE to make an equivalent interaction. Both sites encompass betaArg-412, which was shown by mutational studies to be involved in binding aurovertin. Except for minor changes around the aurovertin pockets, the structure of bovine F1-ATPase is the same as determined previously. Aurovertin B appears to act by preventing closure of the catalytic interfaces, which is essential for a catalytic mechanism involving cyclic interconversion of catalytic sites.

Characterization of the F1F0-ATPase and the tightly-bound ATPase activities in submitochondrial particles from human term placenta

In a previous study we demonstrated the existence of a tightly-bound ATPase in the human placental mitochondria (Martínez et al., 1993). The current study characterizes the ATP hydrolysis produced by the F1F0-ATPase and the tightly-bound ATPase in submitochondrial particles from the human term placenta. Both enzymes were not differentiated by pH. Inhibitors were necessary to distinguish the activity of each enzyme. The kinetic of the total ATP hydrolysis fitted into a model of two enzymes. During the characterization, it was observed that the tightly-bound ATPase activity was partially inhibited by vanadate and Mg2+, whereas the F1F0-ATPase was totally inhibited by Mg2+. Different nucleotides were hydrolyzed by the tightly-bound ATPase; the F1F0-ATPase hydrolyzed exclusively ATP. Glucose-6-phosphate, p-nitrophenylphosphate, or pyrophosphate were not hydrolyzed by the F1F0-ATPase, although some hydrolysis was observed with the tightly-bound ATPase. It is concluded that the tightly-bound ATPase activity corresponded to a 5'-nucelotidase, and that the human placental mitochondria could participate in the metabolism of nucleotides.

Electron transport phosphorylation driven by glyoxylate respiration with hydrogen as electron donor in membrane vesicles of a glyoxylate-fermenting bacterium

The syntrophically glycolate-fermenting bacterium in the methanogenic binary coculture FlGlyM was isolated in pure culture (strain FlGlyR) with glyoxylate as sole substrate. This strain disproportionated 12 glyoxylate to 7 glycolate, 10 CO2, and 3 hydrogen. Glyoxylate was oxidized via the malyl-CoA pathway. All enzymes of this pathway, i.e. malyl-CoA lyase/malate: CoA ligase, malic enzyme, and pyruvate synthase, were demonstrated in cell-free extracts. Glycolate dehydrogenase, hydrogenase, and ATPase, as well as menaquinones as potential electron carriers, were present in the membranes. Everted membrane vesicles catalyzed hydrogen-dependent glyoxylate reduction to glycolate [86-207 nmol min-1 (mg protein)-1] coupled to ATP synthesis from ADP and Pi [38-82 nmol min-1 (mg protein)-1)]. ATP synthesis was abolished entirely by protonophores or ATPase inhibitors (up to 98 and 94% inhibition, respectively) indicating the involvement of proton-motive force in an electron transport phosphorylation driven by a new glyoxylate respiration with hydrogen as electron donor. Measured reaction rates in vesicle preparations revealed a stoichiometry of ATP formation of 0.2-0.5 ATP per glyoxylate reduced.

Inhibition by trifluoperazine of ATP synthesis and hydrolysis by particulate and soluble mitochondrial F1: competition with H2PO4-

The effect of trifluoperazine (TFP) on the ATPase activity of soluble and particulate F1-ATPase and on ATP synthesis driven by succinate oxidation in submitochondrial particles from bovine heart was studied at pH 7.4 and 8.8. At the two pH, TFP inhibited ATP hydrolysis. Inorganic phosphate protected against the inhibiting action of TFP. The results on the effect of various concentrations of phosphate in the reversal of the action of TFP on hydrolysis at pH 7.4 and 8.8 showed that H2PO4- is the species that competes with TFP. The effect of TFP on oxidative phosphorylation was studied at concentrations that do not produce uncoupling or affect the aerobic oxidation of succinate (< 15 microM). TFP inhibited oxidative phosphorylation to a higher extent at pH 8.8 than at pH 7.4; this was through a diminution in the Vmax, and an increase in the Km for phosphate. Data on phosphate uptake during oxidative phosphorylation at several pH showed that H2PO4- is the true substrate for oxidative phosphorylation. Thus, in both synthesis and hydrolysis of ATP, TFP and H2PO4- interact with a common site. However, there is a difference in the sensitivity to TFP of ATP synthesis and hydrolysis; this is more noticeable at pH 8.8, i.e., ATPase activity of soluble F1 remains at about 40% of the activity of the control in a concentration range of TFP of 40-100 microM, whereas in oxidative phosphorylation 14 microM TFP produces a 60% inhibition of phosphate uptake.

ATP-dependent transport of the linear renin-inhibiting peptide EMD 51921 by canalicular plasma membrane vesicles of rat liver: evidence of drug-stimulatable ATP-hydrolysis

Certain peptide drugs, such as the linear hydrophobic renin-inhibitor EMD 51921, are rapidly eliminated via the bile. At the sinosoidal membrane of liver cells EMD 51921 is taken up via a sodium-independent carrier-mediated mechanism, competing for the uptake of bile acids. Until now, the mechanisms of biliary excretion of EMD 51921 were unknown. In this study we describe an ATP-dependent transport system for the enzymatically and metabolically stable hydrophobic linear renin-inhibiting peptide EMD 51921. The ATP-dependent uptake into the osmotic reactive intravesicular space is saturable (Km 12 microM, Vmax 663 pmol/min per mg protein), temperature dependent and specifically requires ATP. Transport is inhibited by vanadate but not by ouabain, EGTA or NaN3, and does not function in basolateral plasma membrane vesicles. Transport is not altered in canalicular membrane vesicles isolated from Tr- rats lacking the canalicular ATP-dependent transport of cysteinyl leukotrienes and related anions. Transport is inhibited by taurocholate, a typical substrate of the canalicular ATP-dependent bile acid transporter, but also by vincristine and daunomycin, substrates of P-glycoproteins. EMD 51921, however, only inhibits the uptake of taurocholate, whereas the transport of daunomycin is not influenced. Taurocholate and EMD 51921 are mutually non- or un-competitive transport inhibitors. Incubation of rat liver canalicular membranes with micromolar concentrations of EMD 51921 resulted in a 1.8-2.5-fold increase in the rate of ATP-hydrolysis. In contrast, ATP-hydrolysis was not affected by fragments of the peptide that are not transported in an ATP-dependent manner. The apparent Km value (EMD) for ATP-hydrolysis is 68 microM. Vmax is 0.032 U/mg protein. ATPase activity is pH dependent. Stimulation of ATP-hydrolysis is inhibited by vanadate, NEM, hydroxymercuribenzoate and ascorbate, but is not affected by ouabain, EGTA or NaN3. EMD 51921 does not stimulate the ATPase activity of the Na+/K(+)-ATPase isolated from kidney medulla. The EMD-stimulatable ATPase seems to be distinct from the glutathione-S-conjugate stimulatable ATPase and the mdr 1a/b gene products and differs in its characteristics from that of the canalicular ecto-ATPase.

Cross-reconstitution studies with polypeptides of Escherichia coli and bovine heart mitochondrial F0F1 ATP synthase

To characterize the role of supernumerary subunits of the mammalian F0F1 ATP synthase, cross-reconstitution of mitochondrial and bacterial F0F1 complexes has been carried out. Escherichia coli F1 (EcF1) can be reconstituted with F1-stripped everted membranes of E. coli (UPEc) and of bovine heart mitochondria (USMP). Bovine heart mitochondrial F1 (BHF1) can also be reconstituted with both membranes. Both EcF1 and BHF1, when reconstituted with UPEc, exhibited oligomycin-insensitive ATP-hydrolase activity. Subunits of the mammalian F0, in particular F0I-PVP protein, F6 and oligomycin-sensitivity-conferring protein (OSCP) conferred oligomycin sensitivity to the catalytic activity of EcF1 or BHF1 reconstituted with UPEc. Reaction of N,N'-dicyclohexylcarbodiimide and development of inhibition of passive H+ conduction was, in UPEc, considerably slower and exhibited a lower apparent affinity than in USMP. The ATP hydrolase activity of UPEc+EcF1 or UPEc+BHF1 was, also, less sensitive to inhibition by N,N'-dicyclohexylcarbodiimide than USMP+EcF1 or USMP+BHF1. Addition of mitochondrial F0I-PVP to UPEc enhanced the sensitivity of H+ conduction to oligomycin. F0I-PVP and OSCP added to UPEc, promoted inhibition by N,N'-dicyclohexylcarbodiimide of passive H+ conduction and increased its binding affinity to subunit c of E. coli F0. The presence of F0I-PVP and OSCP also promoted inhibition by N,N'-dicyclohexylcarbodiimide of the ATP-hydrolase activity of EcF1 or BHF1 reconstituted with UPEc.

Construction, expression and characterization of a plasmid-encoded Na(+)-specific ATPase hybrid consisting of Propionigenium modestum F0-ATPase and Escherichia coli F1-ATPase

The Escherichia coli strain DK8, a deletion mutant lacking the complete unc operon, was transformed with a plasmid containing the genes encoding the a, b, c, delta and part of the alpha subunit of the Na(+)-dependent ATPase of Propionigenium modestum and the genes encoding the alpha, gamma, beta and epsilon subunits of the H(+)-dependent E. coli ATPase. The transformants showed Na(+)-dependent growth on succinate as non-fermentable carbon source. The functionally expressed hybrid ATPase was activated 13-fold at pH 7.5 by the addition of Na+ and inhibited by 1,3-dicyclohexylcarbodiimide, azide and tributyltin chloride. At pH 7.5 and pH 9.0, the hybrid enzyme was protected from inhibition by 1,3-dicyclohexylcarbodiimide in the presence of 50 mM NaCl and 5 mM NaCl, respectively. The hybrid ATPase was reconstituted into proteoliposomes and catalyzed the transport of Na+ upon ATP addition. ATP-dependent fluorescence quenching of 9-amino-6-chloro-2-methoxyacridine proved that the ATPase hybrid was able to pump protons in the absence of Na+. Furthermore, ATP synthesis could be measured under conditions where a valinomycin-mediated K+ diffusion potential (delta psi) and a Na+ concentration gradient (delta p Na+) were imposed.