Coupling factor ATPase complex of Rhodospirillum rubrum. Purification and properties of a reconstitutively active single subunit

A novel biosensor regulated by the rotator of F₀F₁-ATPase to detect deoxynivalenol rapidly

A novel biosensor (immuno-rotary biosensor) was developed by conjugating deoxynivalenol (DON) monoclonal antibodies with the "rotator" ε-subunit of F(0)F(1)-ATPase within chromatophores with an ε-subunit monoclonal antibody-biotin-avidin-biotin linker to capture DON residues. The conjugation conditions were then optimized. The capture of DON was based on the antibody-antigen reaction and it is indicated by the change in ATP synthetic activity of F(0)F(1)-ATPase, which is measured via chemiluminescence using the luciferin-luciferase system with a computerized microplate luminometer analyzer. 10(-7)mg/ml of DON can be detected. The whole detection process requires only about 20min. This method has promising applications in the detection of small molecular compounds because of its rapidity, simplicity, and sensitivity.

FoF1-ATPase, rotary motor and biosensor

F(o)F(1)-ATPase is an amazing molecular rotary motor at the nanoscale. Single molecule technologies have contributed much to the understanding of the motor. For example, fluorescence imaging and spectroscopy revealed the physical rotation of isolated F(1) and F(o), or F(o)F(1) holoenzyme. Magnetic tweezers were employed to manipulate the ATP synthesis/hydrolysis in F(1), and proton translation in F(o). Here, we briefly review our recent works including a systematic kinetics study of the holoenzyme, the mechanochemical coupling mechanism, reconstituting the delta-free F(o)F(1)-ATPase, direct observation of F(o) rotation at single molecule level and activity regulation through external links on the stator.

F0F1-ATPase activity regulated by external links on beta subunits

F(o)F(1)-ATPase activity is regulated by external links on beta subunits with different molecular weight. It is inhibited when anti-beta subunit antibody, streptavidin and H9 antibody link on the beta subunits successively, but is activated when virus was binded. Western blotting indicated that the employed anti-beta antibody target was on the non-catalytic site of the beta subunit. Furthermore, an ESR study of spin-labeled ATP (SL-ATP) showed that the affinity of ATP to the holoenzyme increases with increasing external links on the beta subunits. This simple regulation method may have great potential in the design of rapid, free labeled, sensitive and selective biosensors.

Catalysis by isolated beta-subunits of the ATP Synthase/ATPase from Thermophilic bacillus PS3. Hydrolysis of pyrophosphate

Although the capacity of isolated beta-subunits of the ATP synthase/ATPase to perform catalysis has been extensively studied, the results have not conclusively shown that the subunits are catalytically active. Since soluble F(1) of mitochondrial H(+)-ATPase can bind inorganic pyrophosphate (PP(i)) and synthesize PP(i) from medium phosphate, we examined if purified His-tagged beta-subunits from Thermophilic bacillus PS3 can hydrolyze PP(i). The difference spectra in the near UV CD of beta-subunits with and without PP(i) show that PP(i) binds to the subunits. Other studies show that beta-subunits hydrolyze [(32)P] PP(i) through a Mg(2+)-dependent process with an optimal pH of 8.3. Free Mg(2+) is required for maximal hydrolytic rates. The Km for PP(i) is 75 microM and the Vmax is 800 pmol/min/mg. ATP is a weak inhibitor of the reaction, it diminishes the Vmax and increases the Km for PP(i). Thus, isolated beta-subunits are catalytically competent with PP(i) as substrate; apparently, the assembly of beta-subunits into the ATPase complex changes substrate specificity, and leads to an increase in catalytic rates.

Green and orange CdTe quantum dots as effective pH-sensitive fluorescent probes for dual simultaneous and independent detection of viruses

One of the most highlighted and fastest moving interfaces of nanotechnology is the application of quantum dots (QDs) in biology. The unparalleled advantages of the size-tunable fluorescent emission and the simultaneous excitation at a single wavelength make QDs the great possibility for use in optical encoding detection. In this paper, we report that green and orange CdTe QDs as convenient, cheap, reversible, and effective pH-sensitive fluorescent probes could monitor the proton (H+) flux driven by ATP synthesis for dual simultaneous and independent detection of viruses on the basis of antibody-antigen reactions. A new kind of biosensor (consisting of the mixture of green-QDs-labeled chromatophores and orange-QDs-labeled chromatophores) fluorescent measurement system was established for rapid, simultaneous, and independent detection of two different kinds of viruses (i.e., H9 avian influenza virus and MHV68 virus). It is crucial to find that the green and orange QDs labeled biosensors coexisting in the detection system can work independently and do not interfere with each another in the fluorescence assays. In addition, a primary steady electric double layer (EDL) model for the QDs biosensors was proposed to illustrate the mechanism of simultaneous and independent detection of the biosensors. We believe that the pH-sensitive CdTe QDs based detection system, described in this paper, is an important step toward optical encoding and has a great potential for simultaneous and independent qualitative and quantitative multiple detection systems.

Using giant unilamellar lipid vesicle micro-patterns as ultrasmall reaction containers to observe reversible ATP synthesis/hydrolysis of F0F1-ATPase directly

F(0)F(1)-ATPase within chromatophores, which was labeled with pH-sensitive quantum dots, was encapsulated in large unilamellar lipid vesicles (LUVs) through reverse-phase evaporation. Then a microarray of chromatophore-containing LUVs was created using a micro-contact printing (mu-CP) technique. Through controlled dehydration-rehydration of the lipid patterns, a microarray of single chromatophore-containing giant unilamellar lipid vesicles (GUVs) was formed with desired size and uniform shape. The reversible ATP synthesis/hydrolysis of F(0)F(1)-ATPase in GUVs was directly observed by fluorescence microscopy through the fluorescence intensity increase/decrease in the pH-sensitive quantum dots labeled on the outer surface of the chromatophore. To the best of our knowledge, this is the first direct observation of the reversible behavior of F(0)F(1)-ATPase at the bulk scale.

Using cadmium telluride quantum dots as a proton flux sensor and applying to detect H9 avian influenza virus

Semiconductor nanocrystals, often known as quantum dots, have been used extensively for a wide range of applications in bioimaging and biosensing. In this article, we report that the pH-sensitive cadmium telluride (CdTe) quantum dots (QDs) were used as a proton sensor to detect proton flux that was driven by ATP synthesis in chromatophores. To confirm that these QD-labeled chromatophores were responding to proton flux pumping driven by ATP synthesis, N,N'-dicyclohexylcarbodiimide (DCCD) was used as an inhibitor of ATPase activity. Furthermore, we applied the QD-labeled chromatophores as a virus detector to detect the H9 avian influenza virus based on antibody-antigen reaction. The results showed that this QD virus detector could be a new virus-detecting device.

Mechanically driven proton conduction in single δ-free F0F1-ATPase

In order to observe mechanically driven proton flux in F(0)F(1)-ATPase coupled with artificial driven rotation on F(1) simultaneously, a double channel observation system was established. An artificial delta-free F(0)F(1)-ATPase was constructed with alpha(3), beta(3), epsilon, gamma, and c(n) subunits as rotator and a, b(2) as stator. The chromatophore was immobilized on the glass surface through biotin-streptavidin-biotin system, and the magnetic bead was attached to the beta subunit of delta-free F(0)F(1)-ATPase. The mechanically driven proton flux was indicated by the fluorescence intensity change of fluorescein reference standard (F1300) and recorded by a cooled digital CCD camera. The mechanochemical coupling stoichiometry between F(0) and F(1) is about 4.15 +/- 0.2H(+)/rev when the magnetic field rotated at 0.33 Hz (rps).

F0F1-ATPase as biosensor to detect single virus

F(0)F(1)-ATPase within chromatophore was constructed as a biosensor (immuno-rotary biosensor) for the purpose of capturing single virus. Capture of virus was based on antibody-antigen reaction. The detection of virus based on proton flux change driven by ATP-synthesis of F(0)F(1)-ATPase, which was indicated by F1300, was directly observed by a fluorescence microscope. The results demonstrate that the biosensor loading of virus particles has remarkable signal-to-noise ratio (3.8:1) compared to its control at single molecular level, and will be convenient, quick, and even super-sensitive for detecting virus particles.

Detecting proton flux across chromatophores driven by F0F1-ATPase using N-(fluorescein-5-thiocarbamoyl)-1,2-dihexadecanoyl-sn-glycero-3-phosphoethanolamine, triethylammonium salt

N-(Fluorescein-5-thiocarbamoyl)-1,2-dihexadecanoyl-sn-glycero-3-phosphoethanolamine, triethylammonium salt (F-DHPE) is a lipid fluorescence dye sensitive to pH changes and is used in this study for detecting proton flux through F0F1-ATPase within chromatophores driven by ATP hydrolysis. F-DHPE is easily labeled to the outer surface of chromatophores. In the range of pH 7.0 to 9.0, fluorescence intensity is sensitive to pH changes. The sensitivity is especially great in the range of pH 8.2 to 9.0, so pH 8.6 was chosen as the appropriate experimental condition. It is shown that added ATP not only acts as a fluorescence quencher but also can be hydrolyzed by F0F1-ATPase to pump protons into chromatophores, resulting in fluorescence restoration. A stimulator (NaSO3) and various types of inhibitors (NaN3, 5'-adenylyl imidodiphosphate [AMP-PNP], and N,N'-dicyclohexylcarbodiimide [DCCD]) of F0F1 confirmed that fluorescence restoration is caused by ATP-driven proton flux. When loaded with one antibody (anti-beta antibody) or two antibodies (anti-beta antibody and sheep to rabbit second antibody), F0F1-ATPase exhibits lower proton pumping activities, as indicated by fluorescence restoration. The possible mechanism of the inhibition of antibodies on proton pumping activity is discussed.

Formation and properties of hybrid photosynthetic F1-ATPases. Demonstration of different structural requirements for stimulation and inhibition by tentoxin

A hybrid ATPase composed of cloned chloroplast ATP synthase beta and gamma subunits (betaC and gammaC) and the cloned alpha subunit from the Rhodospirillum rubrum ATP synthase (alphaR) was assembled using solubilized inclusion bodies and a simple single-step folding procedure. The catalytic properties of the assembled alpha3Rbeta3CgammaC were compared to those of the core alpha3Cbeta3CgammaC complex of the native chloroplast coupling factor 1 (CF1) and to another recently described hybrid enzyme containing R. rubrum alpha and beta subunits and the CF1 gamma subunit (alpha3Rbeta3RgammaC). All three enzymes were similarly stimulated by dithiothreitol and inhibited by copper chloride in response to reduction and oxidation, respectively, of the disulfide bond in the chloroplast gamma subunit. In addition, all three enzymes exhibited the same concentration dependence for inhibition by the CF1 epsilon subunit. Thus the CF1 gamma subunit conferred full redox regulation and normal epsilon binding to the two hybrid enzymes. Only the native CF1 alpha3Cbeta3CgammaC complex was inhibited by tentoxin, confirming the requirement for both CF1 alpha and beta subunits for tentoxin inhibition. However, the alpha3Rbeta3CgammaC complex, like the alpha3Cbeta3CgammaC complex, was stimulated by tentoxin at concentrations in excess of 10 microm. In addition, replacement of the aspartate at position 83 in betaC with leucine resulted in the loss of stimulation in the alpha3Rbeta3CgammaC hybrid. The results indicate that both inhibition and stimulation by tentoxin require a similar structural contribution from the beta subunit, but differ in their requirements for alpha subunit structure.

Mutations in the beta-subunit Thr(159) and Glu(184) of the Rhodospirillum rubrum F(0)F(1) ATP synthase reveal differences in ligands for the coupled Mg(2+)- and decoupled Ca(2+)-dependent F(0)F(1) activities

In the crystal structure of the mitochondrial F(1)-ATPase, the beta-Thr(163) residue was identified as a ligand to Mg(2+) and the beta-Glu(188) as directly involved in catalysis. We replaced the equivalent beta-Thr(159) of the chromatophore F(0)F(1) ATP synthase of Rhodospirillum rubrum with Ser, Ala, or Val and the Glu(184) with Gln or Lys. The mutant beta subunits were isolated and tested for their capacity to assemble into a beta-less chromatophore F(0)F(1) and restore its lost activities. All of them were found to bind into the beta-less enzyme with the same efficiency as the wild type beta subunit, but only the beta-Thr(159) --> Ser mutant restored the activity of the assembled enzyme. These results indicate that both Thr(159) and Glu(184) are not required for assembly and that Glu(184) is indeed essential for all the membrane-bound chromatophore F(0)F(1) activities. A detailed comparison between the wild type and the beta-Thr(159) --> Ser mutant revealed a rather surprising difference. Although this mutant restored the wild type levels and all specific properties of this F(0)F(1) proton-coupled ATP synthesis as well as Mg- and Mn-dependent ATP hydrolysis, it did not restore at all the proton-decoupled CaATPase activity. This clear difference between the ligands for Mg(2+) and Mn(2+), where threonine can be replaced by serine, and Ca(2+), where only threonine is active, suggests that the beta-subunit catalytic site has different conformational states when occupied by Ca(2+) as compared with Mg(2+). These different states might result in different interactions between the beta and gamma subunits, which are involved in linking F(1) catalysis with F(0) proton-translocation and can thus explain the complete absence of Ca-dependent proton-coupled F(0)F(1) catalytic activity.

Hybrid Rhodospirillum rubrum F(0)F(1) ATP synthases containing spinach chloroplast F(1) beta or alpha and beta subunits reveal the essential role of the alpha subunit in ATP synthesis and tentoxin sensitivity

Trace amounts ( approximately 5%) of the chloroplast alpha subunit were found to be absolutely required for effective restoration of catalytic function to LiCl-treated chromatophores of Rhodospirillum rubrum with the chloroplast beta subunit (Avital, S., and Gromet-Elhanan, Z. (1991) J. Biol. Chem. 266, 7067-7072). To clarify the role of the alpha subunit in the rebinding of beta, restoration of catalytic function, and conferral of sensitivity to the chloroplast-specific inhibitor tentoxin, LiCl-treated chromatophores were analyzed by immunoblotting before and after reconstitution with mixtures of R. rubrum and chloroplast alpha and beta subunits. The treated chromatophores were found to have lost, in addition to most of their beta subunits, approximately a third of the alpha subunits, and restoration of catalytic activity required rebinding of both subunits. The hybrid reconstituted with the R. rubrum alpha and chloroplast beta subunits was active in ATP synthesis as well as hydrolysis, and both activities were completely resistant to tentoxin. In contrast, a hybrid reconstituted with both chloroplast alpha and beta subunits restored only a MgATPase activity, which was fully inhibited by tentoxin. These results indicate that all three copies of the R. rubrum alpha subunit are required for proton-coupled ATP synthesis, whereas for conferral of tentoxin sensitivity at least one copy of the chloroplast alpha subunit is required together with the chloroplast beta subunit. The hybrid system was further used to examine the effects of amino acid substitution at position 83 of the beta subunit on sensitivity to tentoxin.

Refolding of recombinant alpha and beta subunits of the Rhodospirillum rubrum F(0)F(1) ATP synthase into functional monomers that reconstitute an active alpha(1)beta(1)-dimer

The alpha subunit from the Rhodospirillum rubrum F(0)F(1) ATP synthase (RrF(1)alpha) was over-expressed in unc operon-deleted Escherichia coli strains under various growth conditions only in insoluble inclusion bodies. The functional refolding of urea-solubilized RrF(1)alpha was followed by measuring its ability to stimulate the restoration of ATP synthesis and hydrolysis in beta-less R. rubrum chromatophores reconstituted with pure native or recombinant RrF(1)beta [Nathanson, L. & Gromet-Elhanan, Z. (1998) J. Biol. Chem. 273, 10933-10938]. The refolding efficiency was found to increase with decreasing RrF(1)alpha concentrations and required high concentrations of MgATP, saturating approximately 60% when 50 microgram protein.mL(-1) were refolded in presence of 50 mM MgATP. Size-exclusion HPLC of such refolded RrF(1)alpha revealed a 50-60% decrease in its aggregated form and a parallel appearance of its monomeric peak. RrF(1)beta refolded under identical conditions appeared almost exclusively as a monomer. This procedure enabled the isolation of large amounts of a stable RrF(1)alpha monomer, which stimulated the restoration of ATP synthesis and hydrolysis much more efficiently than the refolded alpha mixture, and bound ATP and ADP in a Mg-dependent manner. Incubation of both RrF(1)alpha and beta monomers, which by themselves had no ATPase activity, resulted in a parallel appearance of activity and assembled alpha(1)beta(1)-dimers, but showed no formation of alpha(3)beta(3)-hexamers. The RrF(1)-alpha(1)beta(1)-ATPase activity was, however, very similar to the activity observed in isolated native chloroplast CF(1)-alpha(3)beta(3), indicating that these dimers contain only the catalytic nucleotide-binding site at their alpha/beta interface. Their inability to associate into an alpha(3)beta(3)-hexamer seems therefore to reflect a much lower stability of the noncatalytic RrF(1) alpha/beta interface.

Mutagenesis of beta-Glu-195 of the Rhodospirillum rubrum F1-ATPase and its role in divalent cation-dependent catalysis

We introduced mutations at the fully conserved residue Glu-195 in subunit beta of Rhodospirillum rubrum F1-ATPase. The activities of the expressed wild type (WT) and mutant beta subunits were assayed by following their capacity to assemble into the earlier prepared beta-depleted, membrane-bound R. rubrum enzyme (Philosoph, S., Binder, A., and Gromet-Elhanan, Z. (1977) J. Biol. Chem. 252, 8742-8747) and to restore ATP synthesis and/or hydrolysis activity. All three mutations, beta-E195K, beta-E195Q, and beta-E195G, were found to bind as the WTbeta into the beta-depleted enzyme. They restored between 30 and 60% of the WT restored photophosphorylation activity and 16, 45, and 105%, respectively of the CaATPase activity. The mutants required, however, much higher concentrations of divalent cations and could not restore any significant MgATPase or MnATPase activities. Only beta-E195G could restore some of these activities when assayed in the presence of 100 mM sulfite and high MgCl2 or MnCl2 concentrations. These results suggest that the observed difference in restoration of ATP synthesis and CaATPase, as compared with MgATPase and MnATPase, can be due to the tight regulation of the last two activities, resulting in their inhibition at cation/ATP ratios above 0.5. The R. rubrum F1beta-E195 is equivalent to the mitochondrial F1beta-E199, which points into the tunnel leading to the F1 catalytic nucleotide binding sites (Abrahams, J. P., Leslie, A. G. W., Lutter, R., and Walker, J. E. (1994) Nature 370, 621-628). Our findings indicate that this residue, although not an integral part of the F1 catalytic sites, affects divalent cation binding and release of inhibitory MgADP, suggesting its participation in the interconversion of the F1 catalytic sites between different conformational states.

The photosynthetic F1-α 3β 3 and α 1β 1 catalytic core complexes

Minimal photosynthetic catalytic F1(αβ) core complexes, containing equimolar ratios of the α and β subunits, were isolated from membrane-bound spinach chloroplast CF1 and Rhodospirillum rubrum chromatophore RrF1. A CF1-α3β3 hexamer and RrF1-α1β1 dimer, which were purified from the respective F1(αβ) complexes, exhibit lower rates and different properties from their parent F1-ATPases. Most interesting is their complete resistance to inhibition by the general F1 inhibitor azide and the specific CF1 inhibitor tentoxin. These inhibitors were earlier reported to inhibit multisite, but not unisite, catalysis in all sensitive F1-ATPases and were therefore suggested to block catalytic site cooperativity. The absence of this typical property of all F1-ATPases in the α1β1 dimer is consistant with the view that the dimer contains only a single catalytic site. The α3β3 hexamer contains however all F1 catalytic sites. Therefore the observation that CF1-α3β3 can bind tentoxin and is stimulated by it suggests that the F1γ subunit, which is required for obtaining inhibition by tentoxin as well as azide, plays an important role in the cooperative interactions between the F1-catalytic sites.

Identification of subunits required for the catalytic activity of the F1-ATPase

F1 (alpha beta) complexes containing equimolar ratios of the alpha and beta subunits have been shown to function as active ATPases, whereas individually isolated alpha and beta subunits show no real ATPase activity. These results indicate that the single-copy subunits are not required for F1-ATPase activity. The minimal F1 (alpha beta)-core complexes exhibit, however, lower rates and some different properties from those of their parent whole F1 or alpha 3 beta 3 gamma complexes. It is therefore concluded that for obtaining a full spectrum of the characteristic functional properties of an F1-ATPase the presence of the F1-gamma subunit is also required. The implications of these findings on the subunit location of both catalytic and noncatalytic nucleotide binding sites is discussed.

Isolation and characterisation of a functional alpha beta heterodimer from the ATP synthase of Rhodospirillum rubrum

An alpha beta heterodimer of the F1-ATPase of Rhodospirillum rubrum was isolated by extraction of chromatophores with LiCl. Each alpha beta heterodimer contains one tightly bound ADP, which is released upon removal of medium Mg2+. The dimer can be reversibly dissociated by removal of Mg(2+)-ions. The alpha beta heterodimer restores both ATP-synthetic and -hydrolytic activities to LiCl-treated chromatophores, saturation being achieved at approximately 2 mmol alpha beta.mol BChl-1. The heterodimer itself hydrolyses Mg-ATP with an activity distinct from RF1, being unaffected by azide or sulphite ions. The Vmax and Km (ATP) for this Mg(2+)-dependent activity were 110 +/- 10 nmol.min-1.mg protein-1 and 100 +/- 30 microM, respectively. The Km did not differ significantly from that of RF1.

Catalytic properties of β subunit isolated from chloroplast coupling factor 1

The chloroplast coupling factor (CF1) was dissociated into subunits by the freezing-thawing procedure in the presence of 0.5 M NaBr and the β subunit was purified by ion-exchange chromatography on a DEAE-cellulose column. The β subunit did not catalyze ATP hydrolysis either in the presence or in the absence of reagents known to activate Mg(2+)-dependent ATPase activity of CF1. However, it manifested appreciable adenylate kinase-like and ATP-ADP γ-phosphate exchange activities. The adenylate kinase-like activity only slightly depended on Mg(2+) ions. Ethanol, and especially diadenosine pentaphosphate, inhibited the reaction effectively. In contrast, the ATP-ADP exchange activity was Mg(2+)-dependent. Ethanol and diadenosine pentaphosphate were poor inhibitors. Sulfite, the CF1-ATPase activator, and quercetin, its inhibitor, had a minor effect on catalytic activity of the β subunit.

Photosynthetic ATPases: purification, properties, subunit isolation and function

Photosynthetic coupling factor ATPases (F1-ATPases) generally censist of five subunits named α, β, γ, δ and ε in order of decreasing apparent molecular weight. The isolated enzyme has a molecular weight of between 390,000 to 400,000, with the five subunits probably occurring in a 3:3:1:1:1 ratio. Some photosynthetic F1 ATPases are inactive as isolated and require treatment with protease, heat or detergent in order to elicit ATPase activity. This activity is sensitive to inhibition by free divalent cations and appears to be more specific for Ca(2+) vs. Mg(2+) as the metal ion substrate chelate. This preference for Ca(2+) can be explained by the higher inhibition constant for inhibition of ATPase activity by free Ca(2+). Methods for the assay of a Mg-dependent ATPase activity have recently been described. These depend on the presence of organic solvents or detergents in the reaction mixture for assay. The molecular mechanism behind the expression of either the Ca- or Mg-ATPase activities is unknown. F1-ATPases function to couple proton efflux from thylakoid membranes or chromatophores to ATP synthesis. The isolated enzyme may thus also be assayed for the reconstitution of 'coupling activity' to membranes depleted of coupling factor 1.The functions of the five subunits in the complex have been deduced from the results of chemical modification and reconstitution studies. The δ subunit is required for the functional binding of the F1 to the F0. The active site is probably contained in the β (and α) subunit(s). The proposed functions for the γ and ε subunits are, however, still matters of controversy. Coupling factors from a wide variety of species including bacteria, algae, C3 and C4 plants, appear to be immunologically related. The β subunits are the most strongly related, although the α and γ subunits also show significant immunological cross-reactivity. DNA sequence analyses of the genes for the β subunit of CF1 have indicated that the primary sequence of this polypeptide is highly conserved. The genes for the polypeptides of CF1 appear to be located in two cellular compartments. The α, β and ε subunits are coded for on chloroplast DNA, whereas the γ and δ subunits are probably nuclear encoded. Experiments involving protein synthesis by isolated chloroplasts or protein synthesis in the presence of inhibitors specific for one or the other set of ribosomes in the cell suggest the existence of pools of unassembled CF1 subunits. These pools, if they do exist in vivo, probably make up no greater than 1% of the total CF1 content of the cell.

Preparative purification of the subunits of chloroplast and Rhodospirillum rubrum coupling factors by flat-bed electrofocusing in granulated gels

A rapid method for the preparative purification of the subunits of oligomeric proteins like chloroplast and Rhodospirillum rubrum coupling factors is presented. It involves the dissociation of the protein in urea and the separation of its subunits by isoelectric focusing in flat-beds of Sepharose CL-4B or Sephadex G-75 superfine, in the presence of urea and in an overnight run. Using this procedure in the pH range 5-7, we have purified to homogeneity the alpha, beta and delta subunits of chloroplast coupling factor, as well as the alpha and beta subunits of Rhodospirillum rubrum coupling factor. The full separation of the gamma and epsilon subunits of chloroplast coupling factor, which focused at the same pH, was achieved by gel filtration high-performance liquid chromatography.

Antibodies to the F1-ATPase of Rhodospirillum rubrum and its purified native beta-subunit: inhibition of ATP-linked activities in R. rubrum and in lettuce

1. Antibodies prepared against the Rhodospirillum rubrum F1-ATPase (RrF1) and its purified, native-beta-subunit, exhibited cross-reactivity with the following soluble preparations of R. rubrum ATPase: RrF0 . F1, RrF1 and the beta-subunit. Anti-RrF1, but not anti-beta antibodies, also formed precipitin lines with soluble beta-less Rrf1, indicating that antigenic determinants of both the beta-subunit and the other four RrF1-subunits are expressed in the whole RrF1 molecule. Both antibodies agglutinated the R. rubrum chromatophores, suggesting that the beta-subunit is located on the external part of RrF1. 2. Both antibodies inhibited ATP synthesis and hydrolysis activities of R. rubrum chromatophores, as well as all the soluble ATPase reactions. Similar concentrations of each antibody were required for 50% inhibition of all these reactions, but anti-RrF1 was always somewhat more effective than anti-beta. These data indicate that the beta-subunit is involved in the catalytic site of the RrF1-enzyme. 3. The antibodies prepared against R. rubrum F1-ATPase and its beta-subunit could bind the soluble chloroplast F1-ATPase (CF1) and inhibited ATP-linked reactions carried out by chloroplasts and by soluble CF1. In these reactions, unlike in the R. rubrum ones, anti-beta was a more potent inhibitor than the anti-RrF1 antibody. The cross-reaction obtained between the antibodies raised against R. rubrum F1 and its beta-subunit and the chloroplast CF1 indicates the presence of similar antigenic determinants in the photosynthetic prokaryotic and eukaryotic F1-ATPases, which have been conserved during evolution.

Coupling factor ATPase complex of Rhodospirillum rubrum. Purification and characterization of an oligomycin and N,N'-dicyclohexylcarbodiimide-sensitive (Ca+ + Mg2+)-ATPase

An ATPase complex sensitive to the energy transfer inhibitors oligomycin, dicyclohexylcarbodiimide and venturicidin has been solubilized from Rhodospirillum rubrum chromatophores with Triton X-100 and further purified by centrifugation on a glycerol gradient. The partially purified RrFo . F1 contains 13 distinct polypeptide subunits, as revealed by sodium dodecyl sulfate-polyacrylamide gel electrophoresis, including the subunits of the oligomycin-sensitive, water-soluble RrF1 ATPase. The ATPase activity of RrF0 . F1 as that of the membrane-bound enzyme complex depends on Ca2+ or Mg2+ and from detailed kinetic studies it is concluded that the divalent cation-ATP complex is the substrate for both ATPase complexes. Free ATP and free Mg2+ act as competitive inhibitors, with Ki values of 1 mM and 7 muM, respectively. The subunit composition of the purified RrFo . F1 and its similarity to the membrane-bound ATPase with respect to cation dependence and sensitivity to energy transfer inhibitors suggests that it contains all the subunits of the R. rubrum coupling factor-ATPase complex.

Stabilization of rat liver mitochondrial F1-adenosine triphosphatase during chloroform-induced solubilization

1. Isolation of ATPase from rat liver submitochondrial particles by chloroform treatment requires the presence of ATP or ADP during enzyme solubilization. In the absence of adenine nucleotides the enzyme activity is very low although all protein components of F1-ATPase are released. The low concentrations of ATP or ADP required (5 microM) indicate that the high affinity nucleotide-binding sites are involved in enzyme stabilization. Other nucleotides tested (ITP, GTP, UTP, CTP) were found to be less effective. 2. Polyacrylamide gel electrophoresis and immunodiffusion in agar plates revealed that in the absence of adenine nucleotides a fraction of F1-ATPase released by chloroform treatment is split into fragments. The part of the dissociated enzyme molecule has a molecular weight identical with that of a beta-subunit of F1-ATPase. 3. Dissociation of the F1-ATPase molecule could also be prevented by aurovertin. 4. Crude F1-ATPase solubilized by chloroform treatment can be further purified by Sepharose 6B gel filtration. Specific ATPase activity of the purified enzyme was 90 mumol Pi/min per mg protein and the enzyme was composed of five protein subunits (alpha, beta, gamma, delta, epsilon) with molecular weights 58 000, 55 000, 28 000, 13 000 and 8000, respectively. 5. Chloroform-released F1-ATPase from rat liver mitochondria displayed immunochemical cross-reactivity with that isolated from beef heart mitochondria.

Structure and function of H+-ATPase

(1) Extensive studies on proton-translocating ATPase (H+-ATPase) revealed that H+-ATPase is an energy transforming device universally distributed in membranes of almost all kinds of cells. (2) Crystallization of the catalytic portion (F1) of H+-ATPase showed that F1 is a hexagonal molecule with a central hole. The diameter of F1 is about 90 A and its molecular weight is about 380,000. (3) Use of thermophilic F1 permits the complete reconstitution of F1 from its five subunits (alpha, beta, gamma, delta, epsilon) and demonstration of the gate function of the gamma delta epsilon-complex, the catalytic function of beta (supported by alpha and gamma), and the H+-translocating functions of all five subunits. (4) Studies using purified thermostable F0 showed that F0 is an H+-channel portion of H+-ATPase. The direct measurement of H+-flux through F0, sequencing of DCCD-binding protein, and isolation of F1-binding protein are described. (5) The subunit stoichiometry of F1 may be alpha 3 beta 3 gamma delta epsilon. (6) Reconstitution of stable H+-ATPase-liposomes revealed that ATP is directly synthesized by the flow of H+ driven by an electrochemical potential gradient and that H+ is translocated by ATP hydrolysis. This rules out functions for all the hypothetical components that do not belong to H+-ATPase in H+-driven ATP synthesis. The roles of conformation change and other phenomena in ATP synthesis are also discussed.