Functional groups at the catalytic site of F1 adenosine triphosphatase

Probes of inhibition of Escherichia coli F(1)-ATPase by 7-chloro-4-nitrobenz-2-oxa-1,3-diazole in the presence of MgADP and MgATP support a bi-site mechanism of ATP hydrolysis by the enzyme

Binding of MgADP and MgATP to Escherichia coli F(1)-ATPase (EcF(1)) has been assessed by their effects on extent of the enzyme inhibition by 7-chloro-4-nitrobenz-2-oxa-1,3-diazole (NBD-Cl). MgADP at low concentrations (K(d) 1.3 microM) promotes the inhibition, whereas at higher concentrations (K(d) 0.7 mM) EcF(1) is protected from inhibition. The mutant betaY331W-EcF(1) requires much higher MgADP, K(d) of about 10 mM, for protection. Such MgADP binding was not revealed by fluorescence quenching measurements. MgATP partially protects EcF(1) from inactivation by NBD-Cl, but the enzyme remains sensitive to NBD-Cl in the presence of MgATP at concentrations as high as 10 mM. The activating anion selenite in the absence of MgATP partially protects EcF(1) from inhibition by NBD-Cl. A complete protection of EcF(1) from inhibition by NBD-Cl has been observed in the presence of both MgATP and selenite. The results support a bi-site catalytic mechanism for MgATP hydrolysis by F(1)-ATPases and suggest that stimulation of the enzyme activity by activating anions is due to the anion binding to a catalytic site that remains unoccupied at saturating substrate concentration.

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

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

Separate beta subunits are derivatized with 14C and 3H when the bovine heart mitochondrial F1-ATPase is doubly labeled with 7-chloro-4-nitro[14C]benzofurazan and 5'-p-fluorosulfonylbenzoyl[3H]inosine

Tyrosine residues 311 and 345 of the beta subunit of the bovine heart mitochondrial F1-ATPase (MF1) are present on the same peptide when the enzyme is fragmented with cyanogen bromide. Maximal inactivation of MF1 with 7-chloro-4-nitro[14C]benzofurazan [( 14C]Nbf-Cl) derivatizes tyrosine-311 in a single beta subunit. Cyanogen bromide digests of MF1 containing the [14C]Nbf-O-derivative of tyrosine-beta 311 were submitted to reversed-phase HPLC, with and without prior reduction of the nitro group on the incorporated reagent with dithionite. The retention time of the radioactive cyanogen bromide peptide was shifted substantially by reduction. When a cyanogen bromide digest of MF1 inactivated with 5'-p-fluorosulfonylbenzoyl[3H]inosine [( 3H]FSBI), which proceeds with derivatization of tyrosine-345 in a single beta subunit, was submitted to HPLC under the same conditions, the fragment labeled with 3H eluted with the same retention time as the [14C]Nbf-O-derivative before reduction. Doubly labeled enzyme was prepared by first derivatizing Tyr-beta 311 with [14C]Nbf-Cl and then derivatizing tyrosine-beta 345 with [3H]FSBI with and without reducing the [14C]Nbf-O-derivative of tyrosine-beta 311 with dithionite before modification with [3H]FSBI. The doubly labeled enzyme preparations were digested with cyanogen bromide and submitted to HPLC. The 14C and 3H in the cyanogen bromide digest prepared from doubly labeled enzyme not submitted to reduction eluted together. In contrast, the 14C and 3H in the digest prepared from doubly labeled enzyme which had been reduced eluted separately. From these results it is concluded that different beta subunits are derivatized when MF1 is doubly labeled with [14C]Nbf-Cl and [3H]FSBI.

The specific incorporation of labelled aromatic amino acids into proteins through growth of bacteria in the presence of glyphosate. Application to fluorotryptophan labelling to the H(+)-ATPase of Escherichia coli and NMR studies

Growth of Escherichia coli in the presence of glyphosate, an inhibitor of aromatic amino acid biosynthesis, has permitted the production of proton translocating ATPase that is specifically labelled with 5-fluorotryptophan. Five sets of 19F nuclear magnetic resonances are resolved. The use of glyphosate should be of wide applicability in the preparation of proteins labelled in aromatic amino acid residues for NMR studies.

The benzoylarginine peptidase from Treponema denticola (strain ASLM), a human oral spirochaete: evidence for active-site carboxyl groups

The benzoylarginine peptidase of Treponema denticola (strain ASLM; a human oral spirochaete) was progressively and irreversibly inactivated by 1-(ethoxycarbonyl)-2-ethoxy-1, 2-dihydroquinoline, a carboxyl-group reagent. At acidic pH values, reaction of one mole of the modifier per active site of the enzyme resulted in total inactivation of the enzyme. Assuming that this modifier is a specific carboxyl reagent, the data suggest that the inactivation of the T. denticola benzoylarginine peptidase was caused by the modification of one carboxyl group located close to the active site of the enzyme. Results obtained with Woodward's reagent K (N-ethyl-5-phenylisoxazolium 3'-sulphonate) supported these findings. Carbethoxylation with diethylpyrocarbonate effectively inactivated the enzyme, and addition of hydroxylamine at pH 7.0 restored the activity almost totally, suggesting that the pyrocarbonate had reacted with tyrosyl or histidyl residues.

Role of energy in oxidative phosphorylation

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

The effects of exchange-inert metal-nucleotide complexes on the kinetics of beef heart mitochondrial F1-ATPase

The inhibition of beef heart mitochondrial F1 by exchange-inert metal-nucleotide complexes was examined. Mono- and bidentate Cr(NH3)4ATP were found to be mixed noncompetitive inhibitors of F1-catalyzed ATP hydrolysis (values of Ki = 0.5 and 0.1 mM; values of alpha = 0.2 and 24, respectively). Rh(H2O)nATP was also found to be a mixed noncompetitive inhibitor of F1-catalyzed ATP hydrolysis (Ki = 0.3 mM, alpha = 0.7). These compounds were used in a series of dual inhibition experiments, along with mono- and bidentate CrATP and Co(NH3)4ATP. All the exchange-inert metal-nucleotides examined were found to be mutually exclusive inhibitors of F1, indicating that they all bind to the same site(s). It is postulated that the pKa of the metal-coordinated ligands is related to the potency of inhibition by these compounds. It appears probable that the exchange-inert nucleotide complexes are binding to site(s) in addition to the catalytic site(s) of F1.

Structure-function investigations of the membrane (Na+ + Mg2+)-ATPase from Acholeplasma laidlawii B: studies of reactive amino acid residues using group-specific reagents

The purified, lipid-reconstituted (Na+ + Mg2+)-ATPase from Acholeplasma laidlawii B was treated with a variety of reagents which specifically modify various amino acid residues on the enzyme. In all cases reaction of this enzyme with any of the reagents tested results in at least a partial inactivation of its activity. The modification of one reactive lysine by dinitrofluorobenzene, of one reactive arginine by phenylglyoxal, or of two tyrosine residues by 4-chloro-7-nitrobenzo-2-oxa-1,3-diazole or fluorosulfonylbenzoyl adenosine results in a complete inactivation of the enzyme. Partial inactivation of enzymatic activity with N-ethylmaleimide, p-chloromercuribenzene sulfonic acid, dicyclohexylcarbodiimide, and Woodward's reagent K suggests an indirect involvement of sulfhydryl and carboxylic acid groups in the maintenance of enzymatic activity, although inhibition by these reagents may also be the result of nonspecific effects such as subunit crosslinking. These studies also show that all of the subunits of the ATPase can be labeled by aqueous-phase reagents directed at amino groups and phenolic groups, and provide evidence for a specific affinity labeling of the alpha subunit of the enzyme by a nucleotide analog directed at phenolic and/or sulfhydryl groups.

Characterisation of phosphate binding to mitochondrial and bacterial membrane-bound ATP synthase by studies of inhibition with 4-chloro-7-nitrobenzofurazan

The effect of phosphate on the inhibition by 4-chloro-7-nitrobenzofurazan of the ATPase activity of the proton-translocating ATP synthase in heart submitochondrial particles was investigated. Binding of phosphate protected strongly against the inhibition. A dissociation constant of 0.2 mM was determined for the enzyme X Pi complex and shown to be independent of pH in the range 7.0-8.0. The protective effect of phosphate was mimicked by arsenate but not by sulphate or malonate. Similar results were obtained for the enzyme from Paracoccus denitrificans. 2,4-Dinitrophenol enhanced phosphate binding to the mitochondrial enzyme since the protective effect of phosphate was increased. The data are compatible with protection arising from binding of phosphate to a catalytic site.

The inhibition of mitochondrial F1-ATPase by 1,5-difluoro-2,4-dinitrobenzene

1,5-Difluoro-2,4-dinitrobenzene completely inhibits F1-ATPase when it is used at micromolar concentrations and the inhibitor/enzyme molar ratio is equal to 3. The inhibition can be reversed by dithiothreitol treatment. 7-Chloro-4-nitrobenzofurazan treatment of F1-ATPase does not prevent the reaction of the enzyme with 1,5-difluoro-2,4-dinitrobenzene. The 1,5-difluoro-2,4-dinitrobenzene-induced inhibition is thought to be a result of the modification of a tyrosine residue with pK 9.1.

The use of [3H]aniline to identify the essential carboxyl group in the bovine mitochondrial F1-ATPase that reacts with 1-(ethoxycarbonyl)-2-ethoxy-1,2-dihydroquinoline

The inactivation of the bovine heart mitochondrial F1-ATPase with 1-(ethoxycarbonyl)-2-ethoxy-1,2-dihydroquinoline (EEDQ) in the presence of [3H]aniline at pH 7.0 led to the covalent incorporation of 3H into the enzyme. When the ATPase was inactivated by 94% with 0.9 mM EEDQ in the presence of 3.6 mM [3H]aniline in a large-scale experiment in which the protein concentration was 21 mg/ml, 4.2 mol [3H]anilide were formed per mol enzyme, of which 0.35 mol was incorporated per mol of the alpha subunit and 1.0 mol was incorporated per mol of the beta subunit. Examination of a tryptic digest of the isolated alpha subunit revealed that the majority of the 3H was contained in a single tryptic peptide, which, when purified, was shown to contain the [3H]anilide of a glutamic acid residue which corresponds to alpha-Glu-402 of the Escherichia coli F1-ATPase. This residue was labeled to the extent of about 1.0 mol/mol enzyme. Analysis of tryptic peptides purified from the isolated beta subunit showed that 0.8 and 1.5 mol, respectively, of the [3H]anilides of beta-Glu-341 and beta-Glu-199 were formed per mol MF1 during the inactivation of the enzyme at 21 mg/ml. When the ATPase was inactivated by 90% at a protein concentration of 1.7 mg/ml by 0.9 mM EEDQ in the presence of 1.7 mM [3H]aniline, 3.1 mol [3H]anilide were formed per mol enzyme. From the analysis of the radioactive peptides purified from a tryptic digest of the labeled ATPase from this experiment it was estimated that 0.7 mol of the [3H]anilide of alpha-Glu-402, 0.3 mol of the [3H]anilide of beta-Glu-341, and 1.5 mol of the [3H]anilide of beta-Glu-199 were formed per mol F1-ATPase. Since beta-Glu-199 is labeled to the same extent in the two experiments while alpha-Glu-402 and beta-Glu-341 were not, suggests that the modification of beta-Glu-199 is responsible for inactivation of the enzyme by EEDQ.

Differential inhibition of F0F1-ATPase-catalysed reactions in bovine-heart submitochondrial particles by organotin compounds

Preincubation of coupled submitochondrial particles with low concentrations of triorganotin compounds results in complete inhibition of the oligomycin-sensitive ATPase activity without any significant effect on the rate of succinate-driven ATP synthesis. The residual ATP synthetic activity is inhibited by oligomycin and uncouplers. The differential inhibition of ATP synthesis and hydrolysis by the triorganotin compounds examined suggests that the two processes are not 'mirror images' of each other, but that they occur through different routes and that the F1F0-ATPase is at least bifunctional.

The nature of the reaction of an essential tyrosine residue of bovine heart mitochondrial ATPase with 4-chloro-7-nitrobenzofurazan and related compounds

Bovine heart mitochondrial ATPase is inhibited after covalent modification with 4-chloro-7-nitrobenzofuroxan. The kinetics of the reaction are indistinguishable from those for the reaction of an essential tyrosine residue of the ATPase with 4-chloro-7-nitrobenzofurazan that have been described previously [Ferguson et al. (1975) Eur. J. Biochem. 54, 117-126]. 4-Fluoro-7-nitrobenzofurazan inhibits the ATPase with a pseudo-first-order rate constant that is tenfold greater than that for 4-chloro-7-nitrobenzofurazan. These data indicate that the rate-limiting step for reaction of the enzyme with these reagents is formation of a Meisenheimer complex at the C-4 position and that the modified tyrosine is probably on the surface of the protein. No evidence was found for more complex patterns of reactivity of 4-chloro-7-nitrobenzofurazan and its analogues. Both ammonium 4-chloro-7-sulphobenzofurazan and ammonium 4-fluoro-7-sulphobenzofurazan fail to react with the ATPase. The utility of these reagents as alternatives to the nitro derivatives may be limited owing to their slow reaction rates. After modification on tyrosine by 4-chloro-7-nitrobenzofurazan, the nitrobenzofurazan group can be transferred by an intramolecular process to lysine [Ferguson et al. (1975) Eur. J. Biochem. 54, 127-133]. ATPase with the lysine thus modified is shown to be reactive towards 4-chloro-7-nitrobenzofurazan in a manner indistinguishable from the native enzyme. This indicates that the intramolecular transfer occurs at sufficient distance to avoid steric hindrance to the second reaction, and that the lysine does not participate in a neighbouring group effect to enhance the reactivity of the tyrosine.

Identification of the initially NBD-labeled essential tyrosine residue in bovine heart MF1-ATPase

Bovine heart MF1-ATPase was labeled with limiting amounts of [14C]NBD-C1[( 14C]4-chloro-7-nitro-2,1,3-benzoxadiazole) and the resulting radioactive label on the essential Tyr was stabilized by reduction with zinc in the presence of multidentate ligand EDTA and redox mediator 4,4'-dipyridyl. Subsequent treatment of the labeled protein with cyanogen bromide and separation of the reaction mixture by ion-exchange chromatography yielded essentially only one radioactive polypeptide. Further cleavage of this polypeptide with TPCK-trypsin, lactonization of the terminal homoserine residue and reaction with derivatized polystyrene resin gave a shorter peptide attached to the solid support which contained all the radioactivity. Edman degradation showed that the amino acid sequence of this peptide was Glu . Gly . Asn . Asp . Leu . Tyr . His . Glu . Met, which corresponds to residues 192-200 in the beta subunit of bovine heart MF1-ATPase as determined by Runswick and Walker (1983). Since this specifically labeled Tyr-197 is separated by only one amino acid residue from the essential Glu-199 which was labeled specifically with dicyclohexylcarbodiimide by Yoshida et al. (1982) it seems most likely that both Tyr-197 and Glu-199 play direct roles in the catalytic hydrolysis and synthesis of ATP.

The stoichiometry of proton translocation through H+-ATPase of rat-liver mitochondria

The ratio of the number of protons transported directly by H+-ATPase of intact mitochondria and that of the hydrolyzed ATP (the proton translocation quotient) is determined. A special kinetic method which makes possible determination of ATPase and H+-translocase activities in the same experiment has been used to estimate the proton translocation quotient for mitochondrial H+-ATPase. The quotient is found to be, on average, equal to 3.31 mol/mol. It is shown that the protonophore 3,5-di-tert-butyl-4-hydroxybenzylidenemalononitrile can greatly decrease the proton translocation quotient. This supports our assumption concerning a labile coupling between H+-translocase and ATPase in mitochondria [I. A. Gorskaya, K. F. Sholtz, S. A. Moreva, A. V. Kotelnikova (1979) Biochemistry (Engl. Transl. Biokhimiya) 44, 765-770]. A decrease in the translocation quotient in the presence of the protonophore is likely to be due to the ability of this uncoupler to take back the translocated protons into the mitochondrial matrix before their release into the medium. An electrostatic model of the molecular mechanism of H+-translocase and ATPase coupling in the H+-ATPase complex is discussed. The model is in agreement with the results obtained: transport of more than two protons per each hydrolyzed ATP molecule, and variable efficiency of the process.

Effect of pyridine homologues on proton flux through the CF0 . CF1 complex and photophosphorylation in chloroplasts

At concentrations below 1 mM, hydrophobic pyridine homologues decrease the rate of photophosphorylation and light-stimulated hydrolysis of ATP and light-activated exchange of the tightly bound nucleotides in chloroplasts, but increase the rate of the Hill reaction. Unlike uncoupling agents, the presence of the organic base at such low concentrations decreases the rate of light-dependent leakage and has no effect on the efficiency of two-stage photophosphorylation in broken chloroplasts. By assuming that the organic base is bound to independent equivalent sites in the thylakoid membrane, a simple expression can be derived which relates the observed rates of photophosphorylation and light-stimulated hydrolysis of ATP quantitatively to the concentration of the organic base in solution and gives dissociation equilibrium constants which are on the order of the relative hydrophobicities of the pyridine homologues. A possible mechanistic model for the CF0 . CF1 complex is proposed which could serve as the basis for a unified interpretation of the kinetics of proton translocation in illuminated chloroplasts, the steady-state rate of photophosphorylation, the light-stimulated ATPase activity, and the light-activated exchange of tightly bound adenine nucleotides.

Functional groups at the catalytic site of BF1 adenosinetriphosphatase from Escherichia coli

The rates of inactivation of BF1 adenosinetriphosphatase (BF1-ATPase) from Escherichia coli by 7-chloro-4-nitro-2,1,3-benzoxadiazole, 1-fluoro-2,4-dinitrobenzene, 2,4,6-trinitrobenzenesulfonate, phenylglyoxal, and N,N'-dicyclohexylcarbodiimide have been measured in the presence and absence of various concentrations of inorganic phosphate, ADP, ATP, or magnesium ion. Dissociation equilibrium constants and rate constants for the labeling reactions have been deduced from a quantitative treatment of the kinetic data. The results suggest that the essential Tyr, Lys, Arg, and Glu or Asp residues are probably located at the catalytic site of BF1-ATPase and that in addition to steric interference, the effect of charge interaction should also be considered in interpreting the kinetic data on the protection of BF1-ATPase by substrate molecules against inactivation by the above labeling reagents. Examination of the relative values of the rate constants for the labeling reactions in the presence and absence of inorganic phosphate, ADP, ATP, or magnesium ion, respectively, and the effect of NBD label on the rates of labeling of the essential guanidinium, amino, and carboxyl groups suggest that the arrangement of these four functional groups at the catalytic site of BF1 may be similar to that previously proposed for MF1-ATPase from bovine heart; namely, the essential amino group and the unusually reactive phenol group are probably located near the bound inorganic phosphate or the gamma-phosphate group of the bound ATP, the essential guanidinium group is probably located nearer to the alpha- or beta-phosphate group than to the gamma-phosphate group of the bound ATP or the bound inorganic phosphate, and the essential carboxylate group is probably complexed with a magnesium ion which it shares with the bound inorganic phosphate.