Mutants of Escherichia coli K12 unable to grow on non-fermentable carbon substrates

Among a number of mutants unable to utilize non-fermentable carbon substrates, scoring for membrane ATPase and for ATP-driven transhydrogenase activity permitted to distinguish two phenotypes: (A) mutants lacking ATPase and ATPdriven transhydrogenase; (B) one mutant with an ATPase which behaved according to several criteria as released into solution instead of being membrane bound, a.o it exhibited no ATP-driven transhydrogenase activity. All A and B mutants exhibited a common nutritional pattern.The ATPase-deficient group, when scored for ATPase-binding sites on its membrane particles revealed three different subgroups: (1) mutants having free ATPase-binding sites, (2) mutants with ATPase-binding sites made available by the procedure which releases ATPase from wild-type membrane, and (3) mutants with no detectable ATPase-binding sites.Membranes of the mutant B with unbound ATPase also exhibited a deficiency in ATPase-binding sites, but its soluble ATPase was also found unable to bind to ATPase-binding sites of wild type membranes.The double alteration, namely abnormal or inactive ATPase and absence of ATPase-binding sites on the membrane is compatible with a single mutational defect.     

Reconstitution of energy-dependent transhydrogenase in ATPase-negative mutants of Escherichia coli

The aerobic-driven and ATP-driven energy-dependent transhydrogenase activities of membrane particles from two different Ca²⁺, Mg²⁺-activated ATPase-negative mutants of $\text{E.}$$\text{coli}$ were examined. The activities were low or absent in one of the mutants (DL-54). Reconstitution of the aerobic-driven reaction could be obtained by addition to particles from this mutant of DCCD or of a coupling factor prepared from the parent strain. The coupling factor also restored the ATP-driven reaction. In the other mutant (N144) the aerobic-driven activity was unimpaired, and was not affected by DCCD or by the coupling factor. The difference between the two mutants could be rationalized if the coupling factor ATPase had both a stabilizing and an enzymic function.     

Differentiation between mutants of Escherichia coli K defective in oxidative phosphorylation.

Hybrid membrane particles from two mutants of Escherichia coli K12, Bv4 and K11, defective in oxidative phosphorylation, have been prepared, in which ATP-driven membrane energization is restored. A soluble factor of mutant K11 was found to have properties similar to parental crude coupling factor, ATPase (EC 3.6.1.3). Membrane particles of this mutant could not be reconstituted by parental coupling factor. Either parental coupling factor, or the soluble factor of mutant K11 could reconstitute both respiration-driven and ATP-driven energization to membrane particles of mutant Bv14 or to parental particles depleted of ATPase. Mutant Bv4 was found to be devoid of coupoing factor activity, while retaining the ability to hydrolyze ATP. Both mutants possess an ATPase with an altered binding to the membrane. Mutant K11 is impaired in respiration-driven amino acid transport, in contrast to mutant Bv4. The three major subunits of parental Escherichia coli ATPase have been isolated and antibodies have been prepared against these subunits. Antibodies against the largest subunit (alpha component) or against the intact catalytic subunits (alpha + beta components) inhibit both ATP-Pi exchange in the parent organism as well as ATP hydrolytic activity in parent and mutants. Antibodies against the two other subunits (beta or gamma components) also inhibit these two reactions, but were found to be less effective. Mutant N144, which lacks ATPase activity, shows no precipitin lines with anti-alpha, anti-beta, anti-gamma, or anti (alpha + beta) preparations. In contrast, mutants Bv4 and K11, exhibit cross-reactivity with all of the antisera.     

Pleiotropic plasma membrane ATPase mutations of Saccharomyces cerevisiae.

We isolated a large number of mutations in the structural gene for the plasma membrane ATPase (PMA1) of Saccharomyces cerevisiae. These mutations were selected by their resistance to the aminoglycoside antibiotic hygromycin B. Biochemical analysis of purified membrane preparations showed that the plasma membrane ATPase activity of the mutants was reduced as much as 75%. Intragenic complementation of pma1 mutants suggested that the yeast plasma membrane ATPase was a multimeric enzyme. The pma1 mutants were apparently defective in maintaining internal pH; more than half of the mutants were unable to grow either at a low pH or in the presence of a weak acid. Most pma1 mutants were also osmotic pressure sensitive. At a very low temperature (5 degrees C) many pma1 mutants were unable to grow and were arrested as unbudded cells. The three most severely affected mutants were also unable to grow in the presence of NH4+. The most extreme mutant exhibited a severe defect in progression through the cell cycle; on synthetic medium, the cells progressively accumulated nucleus-containing small buds that generally failed to complete bud enlargement and cytokinesis. Most of the pleiotropic phenotypes of pma1 mutants could be suppressed by the addition of 50 mM KCl but not NaCl to the medium.     

Differentiation between mutants of Escherichia coli K12 defective in oxidative phosphorylation

Hybrid membrane particles from two mutants of Escherichia coli K₁₂, B_v4 and K_I1, defective in oxidative phosphorylation, have been prepared, in which ATP-driven membrane energization is restored.

A soluble factor of mutant K_I1 was found to have properties similar to parental crude coupling factor, ATPase (EC 3.6.1.3). Membrane particles of this mutant could not be reconstituted by parental coupling factor. Either parental coupling factor, or the soluble factor of mutant K_I1 could reconstitute both respiration-driven and ATP-driven energization to membrane particles of mutant B_V4 or to parental particles depleted of ATPase. Mutant B_V4 was found to be devoid of coupling factor activity, while retaining the ability to hydrolyze ATP. Both mutants possess an ATPase with an altered binding to the membrane.

Mutant K_I1 is impaired in respiration-driven amino acid transport, in contrast to mutant B_V4.

The three major subunits of parental Escherichia coli ATPase have been isolated and antibodies have been prepared against these subunits. Antibodies against the largestsubunit ( component) or against the intact catalytic subunits ( + β components) inhibit both ATP-P_i exchange in the parent organism as well as ATP hydrolytic activity in parent and mutants. Antibodies against the two other subunits (β or γ components) also inhibit these two reactions, but were found to be less effective. Mutant N_I44, which lacks ATPase activity, shows no precipitin lines with anti-, anti-β, anti-γ, or anti-( + β) preparations. In contrast, mutants B_V4 and K_I1, exhibit cross-reactivity with all of the antisera.     

ATP-driven transhydrogenase provides an example of delocalized chemiosmotic coupling in reconstituted vesicles and in submitochondrial particles

The mechanism of coupling between mitochondrial ATPase (EC 3.6.1.3) and nicotinamide nucleotide transhydrogenase (EC 1.6.1.1) was studied in reconstituted liposomes containing both purified enzymes and compared with their behavior in submitochondrial particles. In order to investigate the mode of coupling between the transhydrogenase and the ATPase by the double-inhibitor and inhibitor-uncoupler methods, suitable inhibitors of transhydrogenase and ATPase were selected. Phenylarsine oxide and A3'-O-(3-(N-(4-azido-2-nitrophenyl)amino)propionyl)-NAD+ were used as transhydrogenase inhibitors, whereas of the various ATPase inhibitors tested aurovertin was found to be the most convenient. The inhibition of the ATP-driven transhydrogenase activity was proportional to the inhibition of both the ATPase and the transhydrogenase. Inhibitor-uncoupler titrations showed an increased sensitivity of the coupled reaction towards carbonyl cyanide p-trifluoromethoxyphenylhydrazone (FCCP)--an uncoupler that preferentially uncouples localized interactions, according to Herweijer et al. (Biochim. Biophys. Acta 849 (1986) 276-287)--when the primary pump was partially inhibited. However, when the secondary pump was partially inhibited the sensitivity towards FCCP remained unchanged. Similar results were obtained with submitochondrial particles. These results are in contrast to those obtained previously with the ATP-driven reverse electron flow. In addition, the amount of uncoupler required for uncoupling of the ATP-driven transhydrogenase was found to be similar to that required for the stimulation of the ATPase activity, both in reconstituted vesicles and in submitochondrial particles. Uncoupling of reversed electron flow to NAD+ required much less uncoupler. On the basis of these results, it is proposed that, in agreement with the chemiosmotic model, the interaction between ATPase and transhydrogenase in reconstituted vesicles as well as in submitochondrial particles occurs through the delta mu H+. In contrast, the energy transfer between ATPase and NADH-ubiquinone oxidoreductase appears to occur via a more direct interaction, according to the above-mentioned results by Herweijer et al.     

Energy transduction in Escherichia coli. Genetic alteration of a membrane polypeptide of the (Ca2+,Mg2+)-ATPase.

Recent genetic analyses of the membrane components involved in energy transduction in Escherichia coli have concentrated on the (Ca2+, Mg2+)-ATPase complex (EC 3.6.1.3). Many mutants have been described with altered biochemical properties and defects in energy-requiring processes such as oxidative phosphorylation, transhydrogenase activity, and active transport of several solutes. This report describes the isolation of a mutant strain of E. coli that is defective in several energy-requiring processes. The strain BG-31 was obtained by "localized mutagenesis" using phage P1c1. The mutation maps at approximately 73.5 min on the E. coli chromosome. Reversion and suppression analyses indicate that the defect is the result of a single amber mutation. This strain is unable to utilize succinate, D-lactate, or malate for growth. Mutant cells are unable to couple the energy derived from the hydrolysis of ATP to the active transport of proline, although coupling of energy derived from electron transport to solute transport appears normal when examined in both cells and isolated membrane vesicles. Isolated membranes of the mutant are unable to couple the energy derived from the hydrolysis of ATP to transhydrogenase activity while they can utilize the energy generated from electron transport to drive transhydrogenase activity. Extracts of strain BG-31 have normal levels of (Ca2+, Mg2+)-ATPase activity. The ATPase portion of the complex, bacterial F1 (BF1), is poorly attached to the membrane portion of the complex. In vitro reconstitution of transhydrogenase activity with stripped membrane fractions and crude preparations of BF1 localize the defect in strain BG-31 to the membrane portion of the complex. Analysis of membranes of the strain BG-31 by acrylamide gel electrophoresis in the presence of sodium dodecyl sulfate demonstrate the absence of a single polypeptide of molecular weight about 54,000 and the appearance of a new polypeptide of lower molecular weight, about 25,000. Analysis of a spontaneous revertant of BG-31 shows complete restoration of the parental phenotype including the gel patterns. The characterization of this mutant provides the first demonstration of the consequences of a structural gene mutation on a polypeptide in the membrane portion of the complex and represents the initial stages in what we hope will be the biochemical definition and functional characterization of this important energy-transducing system.     

Expression of the cloned subunits of Escherichia coli transhydrogenase from separate replicons

The pntA and pntB genes of Escherichia coli, encoding the alpha- and beta-subunits of the pyridine nucleotide transhydrogenase, were cloned individually in two different compatible plasmids into Escherichia coli mutants lacking transhydrogenase activity. Energy-linked and non-energy-linked transhydrogenase activities were produced only in cells carrying both plasmids thus showing that the products of both genes are required for the formation of an active enzyme. ATP-energized transhydrogenase activity was not increased in cells containing amplified levels of the transhydrogenase when the cell membrane ATPase was also amplified. It is suggested that the excess transhydrogenase is effectively uncoupled from the ATPase by compartmentalization in the cell.     

The use of several energy-coupling reactions in characterizing mutants of Escherichia coli K12 defective in oxidative phosphorylation.

Oxidative phosphorylation, ATP-32Pi exchange, ATP-dependent quenching of acridine-dye fluorescence, ATP-dependent transhydrogenase and ATP-dependent transport of thiomethyl beta-D-galactoside are shown to be experimentally equivalent tools to study the functional state of the ATPase complex in Escherichia coli wild-type and mutant strains defective in oxidative phosphorylation. According to these criteria ten mutants in the ATPase complex were classified having lesions in the unc A,B region of the chromosome. The first mutant type lacks ATPase activity, but the membrane-integrated part of the complex remains functional (class I). The second mutant type lacks a functional membrane-integrated part, but retains ATPase activity (class II). The third mutant type is shown to be defective in both parts of the ATPase complex (class III).     

Citreoviridin, a specific inhibitor of the mitochondiral adenosine triphosphatase.

1. Citreoviridin was a potent inhibitor of the soluble mitochondrial ATPase (adenosine triphosphatase) similar to the closely related aurovertins B and D. 2. Citreoviridin inhibited the following mitochondrial energy-linked reactions also: ADP-stimulated respiration in whole mitochondria from ox heart and rat liver; ATP-driven reduction of NAD+ by succinate; ATP-driven NAD transhydrogenase and ATPase from ox heart submitochondrial particles. 3. The dissociation constant (KD) calculated by a simple law-of-mass-action treatment for the citreoviridin--ATPase complex was 0.5--4.2micron for ox-heart mitochondrial preparations and 0.15micron for rat liver mitochondria. 4. Monoacetylation of citreoviridin decreased its inhibitory potency (KD=2--25micron, ox heart; KD=0.7micron, rat liver). Diacetylation greatly decreased the inhibitory potency (KD=60--215micron, ox heart). 5. Hydrogenation of citreoviridin monoacetate diminished its inhibitory potency considerably. 6. No significant enhancement of fluorescence was observed when citreoviridin interacted with the mitochondrial ATPase.     

Energy-linked transhydrogenase. Effects of valinomycin and nigericin on the ATP-driven transhydrogenase reaction catalyzed by reconstituted transhydrogenase-ATPase vesicles

Reconstituted transhydrogenase-ATPase vesicles obtained with purified beef heart transhydrogenase and oligomycin-sensitive ATPase were investigated with respect to the mode of interaction between the two proton pumps, with special reference to the relative contributions of the membrane potential and proton gradient using valinomycin and nigericin in the presence of potassium. In the absence of ionophores and at low ATP concentrations, below 20 microM, the ATPase generated a proton motive force which was predominantly due to a membrane potential, whereas at saturating concentrations of ATP the proton gradient was the predominant component. The ATP-dependence of the rate of the ATP-driven transhydrogenase reaction showed apparent Km values in the low and high ATP concentration range of about 3 and 56 microM, respectively, with a corresponding difference in Vmax of about 3-fold. It is concluded that the reconstituted transhydrogenase can utilize both a membrane potential and a proton gradient, separately or combined, where the relative contributions of these components depend on the activity of the ATPase. In the reconstituted vesicles, the maximally active transhydrogenase is apparently driven by an electrochemical proton gradient where the membrane potential and the proton gradient contribute one-third and two-thirds, respectively. The rate-dependent relative generation of a membrane potential and pH gradient presumably reflects the proton pump characteristics of the ATPase and/or buffering/permeability characteristics of the vesicles rather than the properties of the transhydrogenase per se. These results are discussed in relation to current models for transhydrogenase-linked proton translocation.     

Energy-linked nicotinamide-nucleotide transhydrogenase. Characterization of reconstituted ATP-driven transhydrogenase from beef heart mitochondria

The interaction between pure transhydrogenase and ATPase (Complex V) from beef heart mitochondria was investigated with transhydrogenase-ATPase vesicles in which the two proteins were co-reconstituted by dialysis or dilution procedures. In addition to phosphatidylcholine and phosphatidylethanolamine, reconstitution required phosphatidylserine and lysophosphatidylcholine. Transhydrogenase-ATPase vesicles catalyzed a 20-30-fold stimulation of the reduction of NADP+ or thio-NADP+ by NADH and a 70-fold shift of the apparent equilibrium expressed as the nicotinamide nucleotide ratio [NADPH][NAD+]/[NADP+][NADH]. In both of these respects, the transhydrogenase-ATPase vesicles were severalfold more efficient than beef heart submitochondrial particles. By measuring the ATP-driven transhydrogenase and the oligomycin-sensitive ATPase activities simultaneously and under the same conditions at low ATP concentrations, i.e. below 15 microM, the ATP-driven transhydrogenase/oligomycin-sensitive ATPase activity ratio was found to be about 3. This value is consistent with the stoichiometries of three protons translocated per ATP hydrolyzed and one proton translocated per NADPH formed and with a mechanism where the two enzymes interact through a delocalized proton-motive force.     

The PCNA Interaction Protein Box Sequence in Rad54 Is an Integral Part of Its ATPase Domain and Is Required for Efficient DNA Repair and Recombination

Rad54 is an ATP-driven translocase involved in the genome maintenance pathway of homologous recombination (HR). Although its activity has been implicated in several steps of HR, its exact role(s) at each step are still not fully understood. We have identified a new interaction between Rad54 and the replicative DNA clamp, proliferating cell nuclear antigen (PCNA). This interaction was only mildly weakened by the mutation of two key hydrophobic residues in the highly-conserved PCNA interaction motif (PIP-box) of Rad54 (Rad54-AA). Intriguingly, the rad54-AA mutant cells displayed sensitivity to DNA damage and showed HR defects similar to the null mutant, despite retaining its ability to interact with HR proteins and to be recruited to HR foci in vivo. We therefore surmised that the PCNA interaction might be impaired in vivo and was unable to promote repair synthesis during HR. Indeed, the Rad54-AA mutant was defective in primer extension at the MAT locus as well as in vitro, but additional biochemical analysis revealed that this mutant also had diminished ATPase activity and an inability to promote D-loop formation. Further mutational analysis of the putative PIP-box uncovered that other phenotypically relevant mutants in this domain also resulted in a loss of ATPase activity. Therefore, we have found that although Rad54 interacts with PCNA, the PIP-box motif likely plays only a minor role in stabilizing the PCNA interaction, and rather, this conserved domain is probably an extension of the ATPase domain III.     

Defining the ATPase center of bacteriophage T4 DNA packaging machine: requirement for a catalytic glutamate residue in the large terminase protein gp17

Double-stranded DNA packaging in icosahedral bacteriophages is driven by an ATPase-coupled packaging machine constituted by the portal protein and two non-structural packaging/terminase proteins assembled at the unique portal vertex of the empty viral capsid. Recent studies show that the N-terminal ATPase site of bacteriophage T4 large terminase protein gp17 is critically required for DNA packaging. It is likely that this is the DNA translocating ATPase that powers directional translocation of DNA into the viral capsid. Defining this ATPase center is therefore fundamentally important to understand the mechanism of ATP-driven DNA translocation in viruses. Using combinatorial mutagenesis and biochemical approaches, we have defined the catalytic carboxylate residue that is required for ATP hydrolysis. Although the original catalytic carboxylate hypothesis suggested the presence of a catalytic glutamate between the Walker A (SRQLGKT(161-167)) and Walker B (MIYID(251-255)) motifs, none of the four candidate glutamic acid residues, E198, E208, E220 and E227, is required for function. However, the E256 residue that is immediately adjacent to the putative Walker B aspartic acid residue (D255) exhibited a phenotypic pattern that is consistent with the catalytic carboxylate function. None of the amino acid substitutions, including the highly conservative D and Q, was tolerated. Biochemical analyses showed that the purified E256V, D, and Q mutant gp17s exhibited a complete loss of gp16-stimulated ATPase activity and in vitro DNA packaging activity, whereas their ATP binding and DNA cleavage functions remained intact. The data suggest that the E256 mutants are trapped in an ATP-bound conformation and are unable to catalyze the ATP hydrolysis-transduction cycle that powers DNA translocation. Thus, this study for the first time identified and characterized a catalytic glutamate residue that is involved in the energy transduction mechanism of a viral DNA packaging machine.     

Salmonella typhimurium HfrA, a mutant in which adenosine triphosphate can drive amino acid transport but not energy-dependent nicotinamide nucleotide transhydrogenation.

In contrast with wild-type Salmonella typhimurium LT2, strain HfrA did not have ATP-driven energy-dependent transhydrogenase activity, although ATP-dependent quenching of atebrin fluorescence was normal. Respiration-dependent and energy-independent transhydrogenase, and Ca2+-activated ATPase (adenosine triphosphatase) activities were similar in both strains. Purified ATPases from the two strains had similar specific activities, similar subunit polypeptides, and were equally effective in restoring energy-dependent transhydrogenase activities to membrane particles of strain LT2 from which the ATPase had been stripped. The purified ATPases from both strains could restore respiration-dependent but not ATP-dependent transhydrogenation to stripped particles of strain HfrA. Both strains grew aerobically equally well on salts media containing glucose, malate, succinate, citrate, acetate, pyruvate, fumarate, lactate or aspartate as substrates. Growth on glucose under anaerobic conditions was similar. Strains LT2 and HfrA were equally effective in the accumulation under both aerobic and anaerobic conditions of the amino acids proline, phenylalanine, histidine, lysine, isoleucine and aspartic acid. Inhibition of amino acid accumulation by KCN and dicyclohexylcarbodi-imide occurred to the same extent in both strains. The complete inhibition by dicyclohexylcarbodi-imide of amino acid uptake under anaerobic conditions suggested that ATP could drive amino acid uptake in both strains. The ability of strain HfrA to carry out ATP-dependent transport or quenching of atebrin fluorescence but not ATP-dependent transhydrogenation is different from the wild-type strain and from any previously described energy-coupling mutant. It is difficult to reconcile the properties of this mutant with the chemiosmotic hypothesis.     

Energy-linked and energy-independent transhydrogenase activities inEscherichia coli vesicles

Active transport vesicles ofEscherichia coli were shown to possess low levels of energy-independent and energy-dependent nicotinamide nucleotide transhydrogenase activities. Breakage of such vesicles in a French pressure cell resulted in a fraction which had an 8–10-fold increased respiration- and ATP-driven transhydrogenase activities.Stimulation of the ATPase activity in vesicles with Triton X-100 was also paralleled by a 2-fold increase in the energy-independent transhydrogenase.Disruption of the vesicles similarly resulted in increases in the energy-independent transhydrogenase, NADH and succinate oxidase activities but a decrease in succinate supported proline uptake.In the light of these findings, the ‘sidedness’ of the vesicle membranes is discussed.     

Adenosine 5''-triphosphate-linked transhydrogenase in cytoplasmic membranes of colicin-treated and untreated Escherichia coli.

The adenosine 5'-triphosphate (ATP)-linked transhydrogenase reaction, present in the particulate fractions of Escherichia coli, was previously shown to be inhibited in these fractions when the bacteria were treated with colicins K or El. The purpose of this study was to characterized the ATP-linked transhydrogenase reaction and the colicin-caused inhibition of the reaction in purified cytoplasmic membranes. Particulate fractions from bacteria treated or untreated with colicins were separated on sucrose gradients into cell wall membrane and cytoplasmic membrane fractions. The ATP-linked transhydrogenase reaction was found to be exclusively associated with the cytoplasmic membrane fractions. The reaction was inhibited by carbonylcyanide m-chlorophenlhdrazone, dinitrophenol, N,N'-dicyclohexylcarbodiimide, and trypsin. Although the cytoplasmic membrane fractions were purified from the majoriy of the cell wall membrane and its bound colicins, they showed the inhibitory effects of colicins K and El on the ATP-linked transhydrogenase reaction. The inhibition of ATP-linked transhydrogenase reaction induced by the colicin could not be reversed by subjection the isolated membranes to a variety of physical and chemical treatments. Cytoplasmic membranes depleted of energy-transducing adenosine triphosphatase ATPase) complex (coupling factor) lost the ATP-linked transhydrogenase activity. The ATPase complexes isolated from membranes of bacteria treated or untreated with colicins El or K reconstituted high levels of ATP-linded transhydrogenase activity to depleted membranes of untreated bacteria. The same ATPase complexes reconstituted low levels of activity to depleted membranes of the treated bacteria.     

Inhibition of ATP hydrolysis by thermoalkaliphilic F1Fo-ATP synthase is controlled by the C terminus of the epsilon subunit

The F(1)F(o)-ATP synthases of alkaliphilic bacteria exhibit latent ATPase activity, and for the thermoalkaliphile Bacillus sp. strain TA2.A1, this activity is intrinsic to the F(1) moiety. To study the mechanism of ATPase inhibition, we developed a heterologous expression system in Escherichia coli to produce TA2F(1) complexes from this thermoalkaliphile. Like the native F(1)F(o)-ATP synthase, the recombinant TA2F(1) was blocked in ATP hydrolysis activity, and this activity was stimulated by the detergent lauryldimethylamine oxide. To determine if the C-terminal domain of the epsilon subunit acts as an inhibitor of ATPase activity and if an electrostatic interaction plays a role, a TA2F(1) mutant with either a truncated epsilon subunit [i.e., TA2F(1)(epsilon(DeltaC))] or substitution of basic residues in the second alpha-helix of epsilon with nonpolar alanines [i.e., TA2F(1)(epsilon(6A))] was constructed. Both mutants showed ATP hydrolysis activity at low and high concentrations of ATP. Treatment of the purified F(1)F(o)-ATP synthase and TA2F(1)(epsilon(WT)) complex with proteases revealed that the epsilon subunit was resistant to proteolytic digestion. In contrast, the epsilon subunit of TA2F(1)(epsilon(6A)) was completely degraded by trypsin, indicating that the C-terminal arm was in a conformation where it was no longer protected from proteolytic digestion. In addition, ATPase activity was not further activated by protease treatment when compared to the untreated control, supporting the observation that epsilon was responsible for inhibition of ATPase activity. To study the effect of the alanine substitutions in the epsilon subunit in the entire holoenzyme, we reconstituted recombinant TA2F(1) complexes with F(1)-stripped native membranes of strain TA2.A1. The reconstituted TA2F(o)F(1)(epsilon(WT)) was blocked in ATP hydrolysis and exhibited low levels of ATP-driven proton pumping consistent with the F(1)F(o)-ATP synthase in native membranes. Reconstituted TA2F(o)F(1)(epsilon(6A)) exhibited ATPase activity that correlated with increased ATP-driven proton pumping, confirming that the epsilon subunit also inhibits ATPase activity of TA2F(o)F(1).     

Subunit specific antisera to the Escherichia coli ATP synthase: effects on ATPase activity, energy transduction, and enzyme assembly

We obtained antisera to each of the five subunits (α, β, γ, δ, and ?) of the F₁ portion of the proton-translocating ATPase from Escherichia coli (ECF₁). No cross-reaction between the antiserum to a given subunit and any of the other four subunits was observed by Ouchterlony immunodiffusion. The α antiserum reacted only with the denatured α chain. Antibodies to either subunit β or subunit γ inhibited the ATPase activity of the enzyme. The ATPase activity of the holoenzyme in the everted membrane vesicles was just as sensitive as purified ECF₁ to inhibition by the anti-β or anti-γ serum. A prolonged digestion of ECF₁ with trypsin removed intact γ from ECF₁, but did not alter the sensitivity of the ATPase to inhibition by the anti-γ serum. Proteolytic fragments were isolated from the trypsinized enzyme. They gave an immunoprecipitation band with the anti-γ serum, but none of the other subunit antisera. The antiδ serum detached ECF₁ from everted membrane vesicles and completely blocked both the ATP- and respiration-dependent pyridine nucleotide transhydrogenase, an energylinked membrane function. The δ antiserum had no effect on the ATPase activity of the ECF₁. The e antiserum stimulated the ATPase activity of purified ECF₁ as shown previously (P. P. Laget and J. B. Smith, Arch. Biochem. Biophys.197, 83, 1979), but strongly inhibited the holoenzyme in membrane vesicles. The α antiserum completely blocked the ATP-driven transhydrogenase. The same antiserum maximally inhibited the respiratory chain-driven reaction by only 35%. These observations indicate that the antiserum selectively affected energy transduction mediated by the ATPase. The protonmotive force generated by substrate oxidation was probably not dissipated by the ? antiserum. Adsorbing the δ or ? antiserum with everted membrane vesicles selectively removed those antibodies that reacted with membrane-bound ATPase. The adsorbed sera still reacted strongly with purified ECF₁, and prevented it from restoring ATP-dependent proton translocation in ECF₁-depleted vesicles. Therefore, it appears that more of the δ and the ? subunit is exposed in the purified ECF₁ molecule than in the membrane-bound enzyme.     

The membrane ATPase of Escherichia coli. II. Release into solution,allotopic properties and reconstitution of membrane-bound ATPase

Membrane-bound ATPase of Escherichia coli was released in a soluble form by decreasing the Mg²⁺ concentration to 0.05 mM. The particulate fraction left behind was depleted by more than 90% from its initial ATPase activity.Soluble ATPase exhibits a number of different properties as compared with membrane-bound ATPase. These are a 2-fold increased K_m toward ATP, a shift of 1–1.5 pH units in the pH-dependence curve, a greatly increased resistance to inhibition by N,N′-dicyclohexylcarbodiimide (DCCD) and a stimulation by Dio 9 instead of an inhibition.Upon mixing the soluble fraction and the depleted membrane fraction, the initial properties of native membrane-bound ATPase reappear. This reconstitution requires Mg²⁺ and results in the physical binding of the activity to sedimentable material.Soluble ATPase and depleted membrane can be titrated against each other until an equivalence point is reached, beyond which the component in excess keeps its previous characteristics.During the release procedure, DCCD remains associated with the particulate fraction with conservation of the ATPase-binding sites.Such DCCD-treated depleted membranes behave as a specific inhibitor of soluble ATPase.