The identification of the site of action of NN'-dicyclohexylcarbodi-imide as a proteolipid in mitochondrial membranes

Nutrient-starved, non-replicating Mycobacterium tuberculosis requires respiration, ATP synthase and isocitrate lyase for maintenance of ATP homeostasis and viability

The ability of Mycobacterium tuberculosis to persist in its human host despite extensive chemotherapy is thought to be based on subpopulations of non-replicating phenotypically drug-resistant bacilli. To study the non-growing pathogen, culture models that generate quiescent organisms by either oxygen depletion in nutrient-rich medium (Wayne model) or nutrient deprivation in oxygen-rich medium (Loebel model) have been developed. In contrast to the energy metabolism of Wayne bacilli, little is known about Loebel bacilli. Here we analysed M. tuberculosis under nutrient-starvation conditions. Upon shifting to the non-replicating state the pathogen maintained a fivefold reduced but constant intracellular ATP level. Chemical probing of the F(0)F(1) ATP synthase demonstrated the importance of this enzyme for ATP homeostasis and viability of the nutrient-starved organism. Surprisingly, the specific ATP synthase inhibitor TMC207 did not affect viability and only moderately reduced the intracellular ATP level of nutrient-starved organisms. Depletion of oxygen killed Loebel bacilli, whereas death was prevented by nitrate, suggesting that respiration and an exogenous electron acceptor are required for maintaining viability. Nutrient-starved bacilli lacking the glyoxylate shunt enzyme isocitrate lyase failed to reduce their intracellular ATP level and died, thus establishing a link between ATP control and intermediary metabolism. We conclude that reduction of the ATP level might be an important step in the adaptation of M. tuberculosis to non-growing survival.

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.

Mitochondrial ATPase

Considerable progress has been made in recent years in our understanding of the phosphorylating apparatus in mitochondria, chloroplasts, and bacteria. It has become clear that the structure and the function of the ATP synthesizing apparatus in these widely divergent organisms is similar if not virtually identical. The subunit composition of F1, its molecular architecture, the location and function of substrate binding sites, as well as putative control sites, understanding of the component parts of the oligomycin-sensitive ATPase complex, and the role of these components in the function of the complex all are under active investigation in many laboratories. The developing information and the new insights provided have begun to permit experimental approaches, at the molecular level, to the mode of action of the ATPase in electron-transport-coupled ATP synthesis.

Voltage-gated proton channels and other proton transfer pathways

Proton channels exist in a wide variety of membrane proteins where they transport protons rapidly and efficiently. Usually the proton pathway is formed mainly by water molecules present in the protein, but its function is regulated by titratable groups on critical amino acid residues in the pathway. All proton channels conduct protons by a hydrogen-bonded chain mechanism in which the proton hops from one water or titratable group to the next. Voltage-gated proton channels represent a specific subset of proton channels that have voltage- and time-dependent gating like other ion channels. However, they differ from most ion channels in their extraordinarily high selectivity, tiny conductance, strong temperature and deuterium isotope effects on conductance and gating kinetics, and insensitivity to block by steric occlusion. Gating of H(+) channels is regulated tightly by pH and voltage, ensuring that they open only when the electrochemical gradient is outward. Thus they function to extrude acid from cells. H(+) channels are expressed in many cells. During the respiratory burst in phagocytes, H(+) current compensates for electron extrusion by NADPH oxidase. Most evidence indicates that the H(+) channel is not part of the NADPH oxidase complex, but rather is a distinct and as yet unidentified molecule.

Phosphorylation of a peptide related to subunit c of the F0F1-ATPase/ATP synthase and relationship to permeability transition pore opening in mitochondria

A phosphorylated polypeptide (ScIRP) from the inner membrane of rat liver mitochondria with an apparent molecular mass of 3.5 kDa was found to be immunoreactive with specific antibodies against subunit c of F0F1-ATPase/ATP synthase (Azarashvily, T. S., Tyynelä, J., Baumann, M., Evtodienko, Yu. V., and Saris, N.-E. L. (2000). Biochem. Biophys. Res. Commun. 270, 741-744. In the present paper we show that the dephosphorylation of ScIRP was promoted by the Ca2+-induced mitochondrial permeability transition (MPT) and prevented by cyclosporin A. Preincubation of ScIRP isolated in its dephosphorylated form with the mitochondrial suspension decreased the membrane potential (delta psiM) and the Ca2+-uptake capacity by promoting MPT. Incorporation of ScIRP into black-lipid membranes increased the membrane conductivity by inducing channel formation that was also suppressed by antibodies to subunit c. These data indicate that the phosphorylation level of ScIRP is influenced by the MPT pore state, presumably by stimulation of calcineurin phosphatase by the Ca2+ used to induce MPT. The possibility of ScIRP being part of the MPT pore assembly is discussed in view of its capability to induced channel activity.

Ca(2+)-modulated phosphorylation of a low-molecular-mass polypeptide in rat liver mitochondria: evidence that it is identical with subunit c of F(0)F(1)-ATPase

A 3.5-kDa polypeptide associated with the inner membrane of rat liver was found to be phosphorylated by [gamma-(32)P]ATP, presumably via a cAMP-dependent kinase. The phosphorylation was modulated by [Ca(2+)] in the physiological range, with a minimum at 1 microM and rising fourfold toward lower (10 nM) and higher (10 microM) concentrations. Further characterization of the 3.5-kDa component showed that the polypeptide has the same electrophoretic mobility as subunit c of F(0)F(1)-ATPase and that it selectively binds to antibodies against subunit c.

Preparative electrophoretic method for the purification of a hydrophobic membrane protein: subunit c of the mitochondrial ATP synthase from rat liver

A method is described for the purification of subunit c of ATP synthase from rat liver mitochondria. After sample preparation and solvent extraction, the protein was purified to homogeneity by a single-step preparative electrophoretic procedure, using aqueous buffer and containing lithium dodecyl sulfate. The subunit is an extremely hydrophobic and insoluble protein and all solubilization attempts, using a variety of detergents, were unsuccessful except for lithium dodecyl sulfate. Buffer exchange and FPLC gel filtration removed the detergent from the purified sample, leaving the protein in a soluble form. The mammalian protein is composed of 75 amino acid residues, with a molecular mass of 7602 Da and is classified as a proteolipid. Subunit c accounts for 25 and 85% of the intralysosomal accumulation, within neurons, of storage material in juvenile and late-infantile forms of Batten's disease, respectively. This purification procedure allows access to a continuous supply of pure subunit c from a conventional source such as rat liver and preserves precious autopsy materials. The protein could be used as substrate in future proteolytic studies involving pepstatin-insensitive lysosomal proteases and for raising of more specific antibodies. The procedure could also be adapted/modified and used as a model for purifying other extremely insoluble proteins.

Rotational coupling in the F0F1 ATP synthase

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

Topographical structure of membrane-bound Escherichia coli F1F0 ATP synthase in aqueous buffer

Scanning force microscope images of membrane-bound Escherichia coli ATP synthase F0 complexes have been obtained in aqueous solution. The images show a consistent set of internal features: a ring structure which surrounds a central dimple and contains an asymmetric lateral mass. Images of trypsin-treated F0 complexes, which have lost part of their b subunits, show a reduced asymmetric mass, while images of c-subunit oligomers, which lack both the a and b subunits, show a ring and dimple but do not have an asymmetric mass. These results support models in which the F0 complex contains a ring of 9-12 c subunits with the b subunits located outside this ring, and show that scanning force microscopy is able to provide structural information on membrane proteins of molecular mass less than 200 000 Da.

Late-infantile Batten disease: purification of the subunit c of the mitochondrial ATP synthase from storage material

The accumulation of subunit c of the mitochondrial ATP synthase in late-infantile neuronal lipofuscinosis (LINCL) and juvenile neuronal lipofuscinosis (JNCL) is well documented. The purification of the subunit from diverse sources has been reported previously, although not from the brain of Batten disease patients. This proteolipid has now been purified from late-infantile Batten disease brain. The procedures used were an original combination of the conventional solubilisation, differential centrifugation, organic solvent extractions, preparative gel electrophoresis, and FPLC. Gel filtration of the purified protein indicated molecular mass equal to or greater than 2 x 10(6) Da; however, electrophoresis of this pure protein suggested a molecular mass of approximately 3,500 Da, which is a characteristic of subunit c. The pure protein may be solubilised in aqueous buffer containing < 1% lithium dodecyl sulphate (LDS). The protein binds dicyclohexylcarbodiimide (DCCD) and shows immunoreactivity to antibodies raised against ovine storage bodies.

Relationship of subunit 8 of yeast ATP synthase and the inner mitochondrial membrane. Subunit 8 variants containing multiple lysine residues in the central hydrophobic domain retain function

A molecular genetic approach has been used to test the proposition that the central hydrophobic domain of yeast mitochondrial ATP synthase subunit 8 represents a transmembrane stem in contact with the lipid bilayer. The rationale for this approach is the general inability of membrane bilayers to accomodate unshielded charged residues of polypeptide chains. Non-polar residues at several positions within the central hydrophobic domain of subunit 8 were replaced with the positively charged amino acid lysine. This was done in an attempt to disrupt subunit 8 function, and thereby determine the boundaries of the putative transmembrane stem. Each subunit 8 variant was allotopically expressed in vivo as a mitochondrial import precursor encoded by a nuclear gene. It was found that all variants, which included proteins carrying two lysines at various positions in the hydrophobic domain, exhibited the ability to restore growth of subunit-8-deficient cells on the non-fermentable substrate ethanol. This indicated that the function of none of these subunit 8 variants was severely compromised. There was also no detectable change in the proteolipid characteristics of subunit 8, as defined by the chloroform/methanol solubility properties of variant proteins extracted from membranes following import into isolated mitochondria. These data suggest that subunit 8 is located in a hydrophobic niche in the mitochondrial ATP synthase, probably in contact with other protein subunits of the complex. We conclude that the function of subunit 8 does not necessarily require it to be integrated within the inner mitochondrial membrane, in contact with the lipid bilayer. Our findings also suggest that hydropathy plots, indicating hydrophobic domains within polypeptides, cannot reliably be interpreted as transmembrane helices in the absence of independent evidence.

Identification of F0 subunits in the rat liver mitochondrial F0F1-ATP synthase

In order to identify the subunits constituting the rat liver F0F1-ATP synthase, the complex prepared by selective extraction from the mitochondrial membranes with a detergent followed by purification on a sucrose gradient has been compared to that obtained by immunoprecipitation with an anti-F1 serum. The subunits present in both preparations that are assumed to be authentic components of the complex have been identified. The results show that the total rat liver F0F1-ATP synthase contains at least 13 different proteins, seven of which can be attributed to F0. The following F0 subunits have been identified: the subunit b (migrating as a 24 kDa band in SDS-PAGE), the oligomycin-sensitivity-conferring protein (20 kDa), and F6 (9 kDa) that have N-terminal sequences homologous to the beef-heart ones; the mtDNA encoded subunits 6 (20 kDa) and 8 (less than 7 kDa) that can be synthesized in isolated mitochondria; an additional 20 kDa protein that could be equivalent to the beef heart subunit d.

Hexokinase-binding properties of the mitochondrial VDAC protein: inhibition by DCCD and location of putative DCCD-binding sites

The outer mitochondrial membrane receptor for hexokinase binding has been identified as the VDAC protein, also known as mitochondrial porin. The ability of the receptor to bind hexokinase is inhibited by pretreatment with dicyclohexylcarbodiimide (DCCD). At low concentrations, DCCD inhibits hexokinase binding by covalently labeling the VDAC protein, with no apparent effect on VDAC channel-forming activity. The stoichiometry of [14C]-DCCD labeling is consistent with one to two high-affinity DCCD-binding sites per VDAC monomer. A comparison between the sequence of yeast VDAC and a conserved sequence found at DCCD-binding sites of several membrane proteins showed two sites where the yeast VDAC amino acid sequence appears to be very similar to the conserved DCCD-binding sequence. Both of these sites are located near the C-terminal end of yeast VDAC (residues 257-265 and 275-283). These results are consistent with a model in which the C-terminal end of VDAC is involved in binding to the N-terminal end of hexokinase.

cDNA sequence encoding the 16-kDa proteolipid of chromaffin granules implies gene duplication in the evolution of H+-ATPases

Vacuolar H+-ATPases function in generating protonmotive force across the membranes of organelles connected with the vacuolar system of eukaryotic cells. This family of H+-ATPases is distinct from the two other families of H+-ATPases, the plasma membrane-type and the eubacterial-type. One of the subunits of the vacuolar H+-ATPase binds N,N'-dicyclohexylcarbodiimide (DCCD) and has been implicated in the proton-conducting activity of these enzymes. We have cloned and sequenced the gene encoding the DCCD-binding protein (proteolipid) of the H+-ATPase of bovine chromaffin granules. The gene encodes a highly hydrophobic protein of 15,849 Da. Hydropathy plots revealed four transmembrane segments, one of which contains a glutamic residue that is the likely candidate for the DCCD binding site. Sequence homology with the vacuolar proteolipid and with the proteolipids of eubacterial-type H+-ATPases was detected. The proteolipids from Escherichia coli, spinach chloroplasts, and yeast mitochondria matched better to the NH2-terminal part of the vacuolar protein. The proteolipids of bovine mitochondria and Neurospora mitochondria matched better to the COOH-terminal end of the vacuolar proteolipid. These findings suggest that the proteolipids of the vacuolar H+-ATPases were evolved in parallel with the eubacterial proteolipid, from a common ancestral gene that underwent gene duplication.

Reprogrammed expression of subunit 9 of the mitochondrial ATPase complex of Saccharomyces cerevisiae. Expression in vitro from a chemically synthesized gene and import into isolated mitochondria

A synthetic gene has been designed and constructed by total chemical synthesis as a first step in the functional relocation from the mitochondrion to the nucleus of a gene encoding subunit 9 of the yeast mitochondrial ATPase complex. This gene (NAP9) incorporates codons frequently used in nuclear genes of Saccharomyces cerevisiae and additionally includes a series of unique restriction enzyme cleavage sites to facilitate future systematic manipulations of the gene and its protein product. Following the expression of the NAP9 gene by transcription and translation in vitro, a radiolabelled protein was produced which displayed a gel electrophoretic mobility and solubility in chloroform/methanol characteristic of the authentic subunit 9 proteolipid encoded in vivo by the mitochondrial oli1 gene. In order to achieve import into mitochondria of yeast subunit 9, a fusion was made between the NAP9 gene and DNA encoding the cleavable presequence of the nuclearly encoded precursor to subunit 9 from Neurospora crassa. Following expression in vitro, the resultant fusion protein was imported and appropriately processed by isolated yeast mitochondria. The import of yeast subunit 9 was less efficient than that observed in parallel import experiments with yeast subunit 8 attached to the same presequence or with the naturally occurring intact N. crassa subunit 9 precursor. Yeast subunit 9 lacking a leader sequence is not imported into mitochondria but, unlike subunit 8, it does not embed itself into the outer membrane, in spite of its highly hydrophobic character.

NH2-terminal sequence of the isolated yeast ATP synthase subunit 6 reveals post-translational cleavage

The three mitochondrially translated ATP synthase subunits of Saccharomyces cerevisiae were extracted from the enzyme and from whole mitochondria using an organic solvent mixture and then purified by reverse-phase HPLC. The amino acid composition of subunit 6 is close to the one predicted from the oli2 gene. The partial amino terminal sequence of subunit 6 reveals a post-translational cleavage site between the Thr-10 and Ser-11 residues of the precursor. Thus, mature subunit 6 contains 249 amino acid residues and displays a molecular mass of 27943 Da.

NN'-dicyclohexylcarbodi-imide-sensitivity of bovine heart mitochondrial NADH: ubiquinone oxidoreductase. Inhibition of activity and binding to subunits

Dicyclohexylcarbodi-imide (DCCD) inhibition of NADH: ubiquinone oxidoreductase was studied in submitochondrial particles and in the isolated form, together with the binding of the reagent to the enzyme. DCCD inhibited the isolated enzyme in a time- and concentration-dependent manner. Over the concentration range studied, a maximum inhibition of 85% was attained within 60 min. The time course for the binding of DCCD to the enzyme was similar to that of activity inhibition. The NADH:ubiquinone oxidoreductase activity of the submitochondrial particles was also sensitive to DCCD, and the locus of binding of the inhibitor was studied by subsequent resolution of the enzyme into subunit polypeptides. Only two subunits (molecular masses 13.7 and 21.5 kDa) were labelled by [14C]DCCD, whereas, when the enzyme in its isolated form was treated with [14C]DCCD, six subunits (13.7, 16.1, 21.5, 39, 43 and 53 kDa) were labelled. Comparison with the subunit labelling of F1F0-ATPase and ubiquinol:cytochrome c oxidoreductase indicated that the labelling pattern of NADH:ubiquinone oxidoreductase, and enzyme complex with a multitude of subunits, is unique and not due to contamination by other inner-membrane proteins. The correlation between the electron- and proton-transport functions and the DCCD-binding components remains to be established.

Initiation codons in mammalian mitochondria: differences in genetic code in the organelle

The bovine mitochondrial gene products ND2 and ND4, components of NADH dehydrogenase, have been purified from a chloroform/methanol extract of mitochondrial membranes, and the human mitochondrial gene products ND2 and cytochrome b have been obtained by similar procedures. They have been identified by comparison of their amino-terminal protein sequences with those predicted from DNA sequences of bovine and human mitochondrial DNA. All of the proteins have methionine as their amino-terminal residue. In bovine ND2, this residue is encoded by the "universal" isoleucine codon AUA, and the sequences of human cytochrome b and bovine ND2 demonstrate that AUA also encodes methionine in the elongation step of mitochondrial protein synthesis. In human ND2, the amino-terminal methionine is encoded by AUU, which, as in the "universal" genetic code, is also used as an isoleucine codon in elongation. Thus, AUU has a dual coding function which is dependent upon its context.

The binding of DNA to water soluble carbodiimide modified proteins

Bovine serum albumin and human serum transferrin modified by the water soluble carbodiimides N-ethyl-N'-(3-dimethyl propylamino) carbodiimide (CDI) or N-ethyl-N'-(3-trimethyl propylammonium) carbodiimide (Me+CDI) to yield N-acylurea proteins bind pBR322 DNA reversibly showing electrostatic and non-electrostatic components in the binding energies (delta G overall). It is proposed that initially an electrostatic interaction arises from ion pair formation between the DNA phosphates and the N-acylurea entities. This is consolidated, in single stranded regions, by a second event in which it is suggested that the base guanine interacts with elements of the N-acylurea moieties through hydrogen bonding or a glyoxal-type addition.

Electrophoretic behavior of the H+-ATPase proteolipid from bovine heart mitochondria

The proteolipid subunit of H+-ATPase was labeled by [14C]N,N'-dicyclohexylcarbodiimide in bovine heart mitochondria. The radioactive labeling was followed using various systems of sodium dodecylsulfate polyacrylamide gel electrophoresis (SDS-PAGE). When using discontinuous SDS-PAGE (Laemmli, U.K., 1970, Nature (London) 227, 680-685) a monomeric (Mr 7600 +/- 1500) and a dimeric form (Mr 17,800 +/- 1200) of the proteolipid were detected, while only the monomeric form was found on urea (8 M) containing gels (SDS-PAGE according to Laemmli; or Swank, R. T., and Munkers, K. D., 1971, Anal. Biochem. 39, 462-477). When using SDS-PAGE with Na-Pi buffer (Weber, K., and Osborn, M., 1969, J. Biol. Chem. 244, 4406-4442), only a dimeric form of the proteolipid (Mr 15,000 +/- 1000) was detected. Experimental data indicate that the different patterns of proteolipid separation are related to the presence of the two distinct proteolipid conformations in the SDS solution.

Characterization of native and reconstituted hydrogen ion pumping adenosinetriphosphatase of chromaffin granules

The ATP-dependent H+ pump from adrenal chromaffin granules is, like the platelet-dense granule H+ pump, essentially insensitive to the mitochondrial ATPase inhibitors sodium azide, efrapeptin, and oligomycin and also insensitive to vanadate and ouabain, agents that inhibit the Na+,K+-ATPase. The chromaffin granule H+ pump is, however, sensitive to low concentrations of NEM (N-ethylmaleimide) and Nbd-Cl (7-chloro-4-nitro-2,1,3-benzoxadiazole). These transport ATPases may thus belong to a new class of ATP-dependent ion pumps distinct from F1F0-and phosphoenzyme-type ATPases. Comparisons of ATP hydrolysis with ATP-dependent serotonin transport suggest that approximately 80% of the ATPase activity in purified chromaffin granule membranes is coupled to H+ pumping. Most of the remaining ATPase activity is due to contaminating mitochondrial ATPase and Na+,K+-ATPase. When extracted with cholate and octyl glucoside, the H+ pump is solubilized in a monodisperse form that retains NEM-sensitive ATPase activity. When reconstituted into proteoliposomes with crude brain phospholipid, the extracted enzyme recovers ATP-dependent H+ pumping, which shows the same inhibitor sensitivity and nucleotide dependence as the native pump. These data demonstrate that the predominant ATP hydrolase of chromaffin granule membrane is also responsible for ATP-driven amine transport and granule acidification in both native and reconstituted membranes.

Studies on polypeptide composition, hydrolytic activity and proton conduction of mitochondrial FoF1 H+ ATPase in regenerating rat liver

A study of the FoF1 ATPase complex of mitochondria isolated from regenerating rat liver following partial (70%) hepatectomy is presented. As we have previously reported, ATPase activity in submitochondrial particles prepared from regenerating rat liver 24 h following partial hepatectomy was depressed by 75% with respect to controls (submitochondrial particles from sham-operated animals). Polyacrylamide gel electrophoresis and immunodecoration using an antibody raised against isolated bovine heart F1 sector of the FoF1 ATPase indicated a substantial decrease in F1 content in the mitochondrial membrane from regenerating rat liver. Proton conduction by the FoF1 ATPase complex was studied by following the anaerobic relaxation of the transmembrane proton gradient (delta mu H+) generated by succinate-driven respiration. In control rat-liver submitochondrial particles containing the FoF1 moiety of the ATPase complex, anaerobic relaxation of delta mu H+ showed biphasic kinetics, whilst the same process in particles derived from regenerating rat liver exhibited monophasic kinetics and was significantly more rapid. Oligomycin and N,N-dicyclohexyl carbodiimide [(cHxN)2C] inhibited proton conductance by the F1-Fo ATPase complex in submitochondrial particles from both control and regenerating rat liver. Binding of [14C](cHxN)2C and immunodecoration using an antibody raised against bovine heart oligomycin-sensitivity-conferring protein (OSCP) indicated no difference in the content of either the (cHxN)2C binding protein or OSCP between control and regenerating rat-liver mitochondrial membranes. The results reported show that the structural and functional integrity of the Fo-F1 ATPase of rat liver is severely perturbed during regeneration.

Purification and Characterization of the Soluble F(1)-ATPase of Oat Root Mitochondria

The properties of the soluble moiety (F(1)) of the mitochondrial H(+)-ATPase from oat roots were examined and compared to those of the native mitochondrial membrane-bound enzyme. The chloroform soluble preparation was purified by Sephadex G-200 and DEAE-cellulose chromatography. The purified F(1) preparation contained major polypeptides corresponding to alpha, beta, gamma, delta, and epsilon of apparent molecular mass 58, 55, 35, 22, and 14 kilodaltons, respectively. The purified F(1)-ATPase, like the native enzyme, was inhibited by azide (I(50) = 10 micromolar), nitrate (I(50) = 7-10 millimolar), 4,4'-diisothiocyano-2,2'-stilbene disulfonic acid (I(50) = 1-3 micromolar), and 7-chloro-4-nitrobenzo-2-oxa-1,3-diazole (I(50) = 3 micromolar). F(1)-ATPase activity was stimulated by bicarbonate but not by chloride. In both the native and the F(1)-form of the ATPase, ATP was hydrolyzed in preference to GTP. The results indicate that these properties of the native membrane-bound mitochondrial ATPase have been conserved in the purified F(1). In contrast to the membrane-bound enzyme, the F(1)-ATPase was not inhibited by oligomycin or by N,N'-dicyclohexylcarbodiimide. The mitochondrial F(1)-ATPase from oat roots is analogous to other known F(1)F(0)-ATPases.

Inhibition of (Na+,K+)-ATPase by dicyclohexylcarbodiimide. Evidence for two carboxyl groups that are essential for enzymatic activity

N,N'-Dicyclohexylcarbodiimide (DCCD), a reagent that reacts with carboxyl groups under mild conditions, irreversibly inhibits (Na+,K+)-ATPase activity (measured by using 1 mM ATP) with a pseudo-first-order rate constant of 0.084 min-1 (0.25 mM DCCD and 37 degrees C). The partial activities of the enzyme, including (Na+,K+)-ATPase at 1 microM ATP, Na+-ATPase, and the formation of enzyme-acyl phosphate (E-P), decayed at about one-third the rate at which (Na+,K+)-ATPase at 1 mM ATP was lost. The formation of E-P from inorganic phosphate was unaffected by DCCD while K+-phosphatase activity decayed at the same rate as (Na+,K+)-ATPase measured at 1 mM ATP. The enzyme's substrates (i.e., sodium, potassium, magnesium, and ATP) all decreased the rate of DCCD inactivation of (Na+,K+)-ATPase activity measured at either 1 mM or 1 microM ATP. The concentration dependence of the protection afforded by each substrate is consistent with its binding at a catalytically relevant site. DCCD also causes cross-linking of the enzyme into species of very high molecular weight. This process occurs at about one-tenth the rate at which (Na+,K+)-ATPase activity measured at 1 mM ATP is lost, too slowly to be related to the loss of enzymatic activity. Labeling of the enzyme with [14C]DCCD shows the incorporation of approximately 1 mol of DCCD per mole of large subunit; however, the incorporation is independent of the loss of enzymatic activity. The results presented here suggest that (Na+,K+)-ATPase contains two carboxyl groups that are essential for catalytic activity, in addition to the previously known aspartate residue which is involved in formation of E-P.(ABSTRACT TRUNCATED AT 250 WORDS)

The 35 kDa DCCD-binding protein from pig heart mitochondria is the mitochondrial porin

The protein which can be labelled by low concentrations of dicyclohexylcarbodiimide in the Mr region of 30 000-35 000 has been purified from pig heart mitochondria with a high yield and as a single band of apparent Mr 35 000 in dodecyl sulphate-containing gels. The protein is not identical with the phosphate carrier as suggested before, since the two proteins behave differently during isolation. Incorporation of the isolated 35 kDa dicyclohexylcarbodiimide-binding protein into lipid bilayer membranes causes an increase of the membrane conductance in definite steps, due to the formation of pores. The specific pore-forming activity increases during the purification procedure. The single pore conductance is about 4.0 nS, suggesting a diameter of 1.7 nm of the open pore. The pore conductance is dependent on the voltage across the membrane. Anion permeability of the pore is higher than cation permeability. These properties are similar to those described for isolated mitochondrial and bacterial porins. It is concluded that the 35 kDa dicyclohexylcarbodiimide-binding protein from pig heart mitochondria is identical with porin from outer mitochondrial membrane.

Activation of guinea-pig and bovine neutrophil NADPH oxidase by N,N'-dicyclohexylcarbodiimide

Dicyclohexylcarbodiimide (DCCD) is a potent stimulant of superoxide generation in guinea-pig peritoneal and bovine blood neutrophils. The dependence of DCCD-elicited respiratory burst on the composition of the medium was investigated. At 37 degrees C, the superoxide generation was short-lived and a rapid losses of enzymatic activity was observed; at 0 degree C, the activity could be preserved for hours. Superoxide generation by whole cells was accompanied by exocytic degranulation. Prolonged incubation with DCCD at 37 degrees C resulted also in a progressive loss of cellular integrity evidenced by the release of a fraction of lactate dehydrogenase. Km values of the particulate NADPH oxidase isolated from DCCD-triggered guinea-pig and bovine cells were 31.7 and 50.0 microM, respectively. Cells pre-equilibrated with the potential sensitive dye Di-S-C3-(5) exhibited changes in the transmembrane potential upon stimulation. Stimulation with DCCD resulted also in the release of membrane-associated calcium, indicated by quenching of the fluorescence of chlortetracycline-loaded neutrophils. Both effects were observed also in human neutrophils which did not generate superoxide upon exposure to DCCD. The mechanism of DCCD-induced responses is discussed.

Structure of the membrane-embedded F0 part of F1F0 ATP synthase from Escherichia coli as inferred from labeling with 3-(Trifluoromethyl)-3-(m-[125I]iodophenyl)diazirine

3-(Trifluoromethyl)-3-(m-[125I]iodophenyl)diazirine [( 125I]TID) is a photoactivatable carbene precursor designed to label selectively the hydrophobic core of membranes. We have used this reagent to obtain information on the topological organization of the membrane-embedded subunits of F1F0 ATP synthase from Escherichia coli. The study included [125I]TID labeling of F0 subunits in different structural (conformational) states and Edman degradations of the labeled polypeptides in order to assign the covalently bound radioactivity to individual amino acid residues. Released phenylthiohydantoin amino acids were analyzed by thin-layer chromatography, and the radioactive derivatives were visualized by autoradiography. The data suggest that labeling patterns can be correlated in a meaningful manner with reagent accessibility and hence with protein-lipid contact. Subunit b appears to be anchored to the membrane by a short N-terminal segment. As almost all of the amino acids of this part are accessible to the reagent, it is inferred that this segment has little interaction with the other subunits. In contrast, in the two segments of subunit c that were labeled with [125I]TID, only certain amino acids reacted with the label. The pattern of these labeled residues is compatible with that of tightly packed alpha-helices.

Discrimination between the binding sites of modulators of the H+-translocating ATPase activity in rat liver mitochondrial membranes

The properties of the components of the mitochondrial ATPase which interact with modulators of energy transduction have been examined. The chromatographic behavior and the size of the components which bind trialkyl tins, carbodiimides and uncouplers, have been shown to be different. However, they all appear to be proteolipids with apparent molecular weights around 10,000. On this basis it is proposed that these inhibitors act at different sites in the membrane sector of the ATP synthase of rat liver mitochondria.

Inhibition by dicyclohexylcarbodiimide of ATP synthesis in isolated rat hepatocytes

Dicyclohexylcarbodiimide (DCCD) inhibits, by 50%, ATP synthesis in isolated hepatocytes. This inhibition is associated with DCCD-binding to a proteolipid fraction present in submitochondrial particles.