Preparation and characterization of homogeneous coupling factor 6 from bovine heart mitochondria

Structural and functional characterization of F(o)F(1)-ATP synthase on the extracellular surface of rat hepatocytes

Extracellular ATP formation from ADP and inorganic phosphate, attributed to the activity of a cell surface ATP synthase, has so far only been reported in cultures of some proliferating and tumoral cell lines. We now provide evidence showing the presence of a functionally active ecto-F(o)F(1)-ATP synthase on the plasma membrane of normal tissue cells, i.e. isolated rat hepatocytes. Both confocal microscopy and flow cytometry analysis show the presence of subunits of F(1) (alpha/beta and gamma) and F(o) (F(o)I-PVP(b) and OSCP) moieties of ATP synthase at the surface of rat hepatocytes. This finding is confirmed by immunoblotting analysis of the hepatocyte plasma membrane fraction. The presence of the inhibitor protein IF(1) is also detected on the hepatocyte surface. Activity assays show that the ectopic-ATP synthase can work both in the direction of ATP synthesis and hydrolysis. A proton translocation assay shows that both these mechanisms are accompanied by a transient flux of H(+) and are inhibited by F(1) and F(o)-targeting inhibitors. We hypothesise that ecto-F(o)F(1)-ATP synthase may control the extracellular ADP/ATP ratio, thus contributing to intracellular pH homeostasis.

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.

Total synthesis of human and rat coupling factor-6 amide and pressor effects in the rat

Mitochondrial coupling factor-6 (CF-6) is a component of the ATP synthase complex essential for energy transduction. CF-6, which is localized to the surface of endothelial cells (ECs) and released by shear stress, has been implicated as an endogenous vasoconstrictor. Previous methods of obtaining CF-6 through purification and recombinant methods were laborious and inefficient. Here, we describe the chemical synthesis of human CF-6, (33-108)-NH(2), its C-terminal fragment (55-108)-NH(2), which is termed pCF-6; the rat CF-6, (33-108)-NH(2), its C-terminal fragment pCF-6, (55-108)-NH(2); and two N-terminal fragments of the rat pro-coupling factor-6, (24-52)-NH(2) and (33-52)-NH(2). Biological activities of each peptide were initially screened with bioassays and verified by in vivo studies. Accordingly, intravenous administration of CF-6, pCF-6, rat CF-6, and rat pCF-6 produced a modest but statistically significant increase in blood pressure and heart rate in urethane anesthetized rats, whereas the N-terminal rat pro-coupling factor-6, (24-52)-NH(2) and (33-52)-NH(2) caused no significant pressor response. Thus, the biologically active site probably resides at the C-terminal portion of CF-6 peptides.

Activity and NMR structure of synthetic peptides of the bovine ATPase inhibitor protein, IF1

The protein IF(1) is a natural inhibitor of the mitochondrial F(o)F(1)-ATPase. Many investigators have been prompted to identify the shortest segment of IF(1), retaining its native activity, for use in biomedical applications. Here, the activity of the synthetic peptides IF(1)-(42-58) and IF(1)-(22-46) is correlated to their structure and conformational plasticity determined by CD and [1H]-NMR spectroscopy. Among all the IF(1) segments tested, IF(1)-(42-58) exerts the most potent, pH and temperature dependent activity on the F(o)F(1) complex. The results suggest that, due to its flexible structure, it can fold in helical and/or beta-spiral arrangements that favor the binding to the F(o)F(1) complex, where the native IF(1) binds. IF(1)-(22-46), instead, as it adopts a rigid alpha-helical conformation, it inhibits ATP hydrolysis only in the soluble F(1) moiety.

Alteration in expression of the rat mitochondrial ATPase 6 gene during Pneumocystis carinii infection

BACKGROUND

Pneumocystis carinii causes pneumonia in immunocompromised patients with a high morbidity and mortality rate, but the interaction between this organism and the host cell is not well understood. The purpose of this research was to study the response of host cells to P. carinii infection on a molecular level.

RESULTS

The technique of mRNA differential display was used to detect genes whose expression may be affected by P. carinii infection. The nucleotide sequence of one differentially displayed DNA fragment was found to be identical to that of the rat mitochondrial ATPase 6 gene, which is a subunit of the F0F1-ATP synthase complex. A four-fold increase in expression of this gene was verified by Northern blot analysis of total RNA extracted from P. carinii-infected rat lung versus that from mock-infected rat lung. Localization of the cells containing ATPase 6 mRNA was accomplished by in situ hybridization. In sections of non-infected rat lung, these cells were found lining the distal parts of the respiratory tree and in apical areas of the alveoli. Histological location of these cells suggested that they were Clara cells and type II pneumocytes. This hypothesis was confirmed by co-localizing the mRNAs for ATPase 6 and surfactant protein B (SP-B) to the same cells by two-color fluorescent in situ hybridization.

CONCLUSIONS

The ATPase 6 gene is over expressed during P. carinii infection, and type II pneumocytes and Clara cells are the cell types responsible for this over-expression.

Functional domains of the ATPase inhibitor protein from bovine heart mitochondria

A study is presented of the activity and temperature dependence of the ATPase inhibitor protein (IF(1)) from bovine heart mitochondria and of synthetic partial IF(1) peptides. The results show that the IF(1)-(42-58) peptide is the most potent inhibitory domain of IF(1).

F1 and F0 connections in the bovine mitochondrial ATP synthase: the role of the of alpha subunit N-terminus, oligomycin-sensitivity conferring protein (OCSP) and subunit d

We have studied the functional effect of limited proteolysis by trypsin of the constituent subunits in the native and reconstituted F1F0 complex and isolated F1 of the bovine heart mitochondrial ATP synthase (EC 3.6.1.34). Chemical cross-linking of oligomycin-sensitivity conferring protein (OSCP) with other subunits of the ATP synthase and the consequent functional effects were also investigated. The results obtained show that the alpha subunit N-terminus is essential for the correct, functional connection of F1 to F0. The alpha-subunit N-terminus contacts OSCP which, in turn, contacts the F0I-PVP(b) and the F0-d subunits. The N-terminus of subunit alpha, OSCP, a segment of subunit d and the C-terminal and central region of F0I-PVP(b) subunits are peripherally located with respect to subunits gamma and delta which are completely shielded in the F1F0 complex against trypsin digestion. This qualifies the N-terminus of subunit alpha, OSCP, subunit d and F0I-PVP(b) as components of the lateral element of the stalk. These subunits, rather than being confined at one side of the complex which would leave most of the central part of the gamma subunit uncovered, surround the gamma and the delta subunits located in the central stalk.

Identification of functional domains and critical residues in the adenosinetriphosphatase inhibitor protein of mitochondrial F0F1 ATP synthase

Peptide segments of the inhibitor protein (IF1) of the F0F1 ATP synthase complex from bovine-heart mitochondria have been constructed by chemical synthesis. The IF1-(42-58)-peptide was equally effective as IF1 in inhibiting the ATPase activity of both the F0F1 complex in the mitochondrial membrane deprived of IF1 (SMP) and soluble F1. The IF1-(22-46)-peptide inhibited the ATPase activity in the soluble F1 but had no effect on either the ATPase activity or H+ conduction in SMP. Substitution of the His or Lys residues with Ala in the IF1-(42-58)-peptide decreased the inhibition of ATP hydrolysis. The inhibition exerted by the IF1-(42-58)-peptide on ATP hydrolysis in SMP exhibited a pH dependence, similar to that observed with IF1, which was lost upon replacement of His or Lys with Ala. In soluble F1, inhibition of ATP hydrolysis by IF1, the IF1-(42-58)-peptide and the IF1-(22-46)-peptide was pH dependent when F1 was first incubated with ATP. The IF1-(42-58)-peptide also caused inhibition of passive H+ conduction in SMP. This activity of the synthetic peptide was weaker, as compared to that of IF1, and practically unaffected by substitution of His or Lys with Ala. An antibody against the IF1-(42-58)-synthetic peptide stimulated ATP hydrolysis in the membrane-bound F0F1 complex with associated IF1 but was without effect on H+ conduction. An antibody against IF1 stimulated both processes.

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

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

The F0 subunits of bovine mitochondrial ATP synthase complex: purification, antibody production, and interspecies cross-immunoreactivity

The known subunits of the membrane sector F0 of the bovine mitochondrial ATP synthase complex are subunits b, d, 6, F6, OSCP (oligomycin sensitivity-conferring protein), the DCCD (dicyclohexylcarbodiimide) binding proteolipid, and A6L. The first six subunits were purified from SMP or preparations of the ATP synthase complex, and monospecific antibodies were raised against each. The antisera were shown to be competent for immuno-blotting, and each antiserum recognized a single polypeptide of the expected Mr in preparations of the ATP synthase complex. Immunoblots utilizing antibodies to OSCP and subunits d and 6, which exhibit the same Mr on dodecyl sulfate-polyacrylamide gels, showed clearly that these polypeptides are immunologically distinct. Immunological cross-reactivity was demonstrated between bovine, human, rat, Saccharomyces cerevisiae, Paracoccus denitrificans, and Escherichia coli for subunit 6; between bovine, human, and rat for subunits b, d, OSCP, and F6; and between bovine and rat for the DCCD binding proteolipid. Anti-subunit 6 antiserum, before or after immunopurification against the ATP synthase complex, recognized a single polypeptide in the bovine ATP synthase complex and S. cerevisiae mitochondria, but two polypeptides of different Mr in bovine SMP, human, and rat mitochondria, and Paracoccus and E. coli membranes.

Mitochondrial F0F1 H+-ATP synthase. Characterization of F0 components involved in H+ translocation

The membrane F0 sector of mitochondrial ATP synthase complex was rapidly isolated by direct extraction with CHAPS from F1-depleted submitochondrial particles. The preparation thus obtained is stable and can be reconstituted in artificial phospholipid membranes to result in oligomycin-sensitive proton conduction, or recombined with purified F1 to give the oligomycin-sensitive F0F1-ATPase complex. The F0 preparation and constituent polypeptides were characterized by SDS-polyacrylamide gel electrophoresis and immunoblot analysis. The functional role of F0 polypeptides was examined by means of trypsin digestion and reconstitution studies. It is shown that, in addition to the 8 kDa DCCD-binding protein, the nuclear encoded protein [(1987) J. Mol. Biol. 197, 89-100], characterized as an intrinsic component of F0 (F0I, PVP protein [(1988) FEBS Lett. 237,9-14]) [corrected] is involved in H+ translocation and the sensitivity of this process to the F0 inhibitors, DCCD and oligomycin.

Topological and functional characterization of the F0I subunit of the membrane moiety of the mitochondrial H+-ATP synthase

Using isolated polypeptides of the F0 sector of bovine heart mitochondrial H+-ATPase, antisera were developed detecting specifically two components of F0. These two components were identified as F0I and oligomycin-sensitivity-conferring protein (OSCP) respectively. Both F0I and OSCP were digested by mild trypsin treatment of submitochondrial particles depleted of the catalytic part of H+-ATPase (USMP). Proteolysis was largely prevented by binding of F1 to F0. Proteolysis of F0I resulted in the formation of three immunoreactive, membrane-bound fragments of apparently 26 kDa, 25.5 kDa and 18 kDa, respectively, indicating that F0I contains trypsin-accessible Arg or Lys residues located close to the end and the middle part of the protein, respectively, which are in intimate contact with F1. Digestion of USMP with trypsin resulted in depression of passive H+ conduction through F0 which could be ascribed to proteolysis of F0I.

Isolation and structural characterization of porcine coupling factor 6 from intestinal tissues

A polypeptide purified from an extract of thermostable, porcine intestinal peptides was found to correspond to coupling factor 6, previously known as a component of the mitochondrial oxidative phosphorylation system. The intestinal presence of this peptide offers a new source for preparation of the component in large quantities, and possibly suggests further functions of the polypeptide. Amino acid sequence analysis of this porcine form reveals it to be identical to the bovine form, except for two replacements, at position 62 (Thr in the porcine, Phe/Thr in the bovine form), and position 70 (Ala/Val). The extensive conservation suggests strict structural constraints on the functional properties of the polypeptide.

Bacterial adenosine 5'-triphosphate synthase (F1F0): purification and reconstitution of F0 complexes and biochemical and functional characterization of their subunits

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Inactivation of the mitochondrial ATPase inhibitor protein by chemical modification with diethylpyrocarbonate

Modification of histidine residue(s) by diethylpyrocarbonate treatment of submitochondrial particles obtained by sonication results in inhibition of ATPase activity and stimulation of oligomycin-sensitive H+ conduction. The inhibition of the ATPase (EC 3.6.1.3) activity persisted in F1 isolated from diethylpyrocarbonate-treated submitochondrial particles, which exhibited the absorbance spectrum of modified histidine. Thus the inhibition of the ATPase activity results from histidine modification in F1 subunits. Removal of the natural inhibitor protein from submitochondrial particles resulted in stimulation of proton conduction. After removal of F1 inhibitor protein from the particles the stimulatory effect exerted by diethylpyrocarbonate treatment on proton conduction was lost. Reconstitution experiments showed that purified F1 inhibitor protein lost, after histidine modification, its capacity to inhibit the ATPase activity and proton conduction. These observations show that the stimulation of proton conduction by the ATPase complex effected by diethylpyrocarbonate treatment results from histidine modification in F1 inhibitor protein.

Regulatory role of the ATPase inhibitor protein on proton conduction by mitochondrial H+-ATPase complex

This study shows that the natural inhibitor protein of mitochondrial H+-ATPase complex (IF1) inhibits, in addition to the catalytic activity, the proton conductivity of the complex. The inhibition of ATPase activity by IF1 is less effective in the purified F1 than in submitochondrial particles where F1 is bound to F0. No inhibition of H+ conductivity by F0 is observed in F1-depleted particles.

Primary structure and subunit stoichiometry of F1-ATPase from bovine mitochondria

The enzyme complex F1-ATPase has been isolated from bovine heart mitochondria by gel filtration of the enzyme released by chloroform from sub-mitochondrial particles. The five individual subunits alpha, beta, gamma, delta and epsilon that comprise the complex have been purified from it, and their amino acid sequences determined almost entirely by direct protein sequence analysis. A single overlap in the gamma-subunit was obtained by DNA sequence analysis of a complementary DNA clone isolated from a bovine cDNA library using a mixture of 32 oligonucleotides as the hybridization probe. The alpha, beta, gamma, delta and epsilon subunits contain 509, 480, 272, 146 and 50 amino acids, respectively. Two half cystine residues are present in the alpha-subunit and one in each of the gamma- and epsilon-chains; they are absent from the beta- and delta-subunits. The stoichiometry of subunits in the complex is estimated to be alpha 3 beta 3 gamma 1 delta 1 epsilon 1 and the molecular weight of the complex is 371,135. Mild trypsinolysis of the F1-ATPase complex, which has little effect on the hydrolytic activity of the enzyme, releases peptides from the N-terminal regions of the alpha- and beta-chains only; the C-terminal regions are unaffected. Sequence analysis of the released peptides demonstrates that the N terminals of the alpha- and beta-chains are ragged. In 65% of alpha-chains, the terminus is pyrrolidone carboxylic acid; in the remainder this residue is absent and the chains commence at residue 2, i.e. lysine. In the beta-subunit a minority of chains (16%) have N-terminal glutamine, or its deamidation product, glutamic acid (6%), or the cyclized derivative, pyrrolidone carboxylic acid (5%). A further 28% commence at residue 2, alanine, and 45% at residue 3, serine. The delta-chains also are heterogeneous; in 50% of chains the N-terminal alanine residue is absent. The sequences of the alpha- and beta-chains show that they are weakly homologous, as they are in bacterial F1-ATPases. The sequence of the bovine delta-subunit of F1-ATPase shows that it is the counterpart of the bacterial epsilon-subunit. The bovine epsilon-subunit is not related to any known bacterial or chloroplast H+-ATPase subunit, nor to any other known sequence. The counterpart of the bacterial delta-subunit is bovine oligomycin sensitivity conferral protein, which helps to bind F1 to the inner mitochondrial membrane.(ABSTRACT TRUNCATED AT 400 WORDS)

Cation-dependent reassembly of F0F1-ATPase in submitochondrial particles: evidence for a binding site for F1 on F0 in the absence of F6 and oligomycin sensitivity-conferring protein

Bovine heart submitochondrial particles depleted of F1, OSCP (oligomycin sensitivity-conferring protein), and F6 require the presence of cations to rebind F1. Among the cations tested, NH4+, Cs+, and Rb+ were most efficient, followed by K+, Na+, Li+, Ca2+, and Mg2+. The extent of F1 binding approached that occurring upon supplementation with F6 and/or OSCP, and was similar to the F1 content of particles prior to depletion. In the absence of cations, F6 and/or OSCP were ineffective in promoting the binding of F1 to the depleted particles. The F1 bound to the particles in the presence of cations alone was completely insensitive to oligomycin. It remained bound to the particles after removal of the cation, and could be rendered partially (approximately 50%) or maximally (less than 80%) oligomycin-sensitive upon the subsequent addition of OSCP or of F6 and OSCP, respectively. The surface potential of the particles, as determined by microelectrophoresis, was screened by all cations tested, regardless of their ability to promote the binding of F1; this was in contrast to earlier findings with particles depleted of F1 only, where the ability of cations to promote the rebinding of F1 paralleled their efficiency to neutralize the surface charge of the particle membrane. It is concluded that the effect of cations on the binding of F1 to F1-, F6-, and OSCP-depleted particles is due to a specific interaction of the cations with certain segments or components of the membrane. The results suggest the existence of a binding site for F1 on F0 in addition to the binding site(s) provided by F6 and OSCP.

Interaction between the mitochondrial ATP synthetase and ATPase inhibitor protein. Active/inactive slow pH-dependent transitions of the inhibitor protein

The rate of mitochondrial ATPase inactivation by the naturally occurring inhibitor protein in the presence of saturating ATP and Mg2+ at pH 8.0 depends hyperbolically on the amount of inhibitor added; the upper limit of an apparent first-order constant for the inactivation process is 1.0(-1) at 25 degrees C. A dramatic difference in the inactivation rate is observed when the protein inhibitor is added to the same assay system from either acidic (pH 4.8) or alkaline (pH 8.2) solutions. The slow reversible transition of the inhibitor from its rapidly reacting 'acidic' form to the slow reacting 'alkaline' form occurs when the solution of the protein inhibitor is subjected to a pH-jump from 4.8 to 8.2 (t1/2 approximately 30s at 25 degrees C). The pH-profile of the inhibitor active/inactive equilibrium suggests that a group with pKa approximately 6.5 is involved in the transition. Treatment of the inhibitor protein with a histidine-specific reagent (e.g. diethyl pyrocarbonate) abolishes its inactivating effect on the ATPase activity. It is concluded that the protonation/deprotonation of the inhibitor protein followed by its slow conformational changes is the rate-limiting step in the inhibitor-ATP synthetase interaction.

Increased content of natural ATPase inhibitor in tumor mitochondria

The ATPase activity of Zajdela hepatoma and Yoshida sarcoma submitochondrial particles was several times lower than the enzyme activity in rat heart and rat liver submitochondrial particles. The content of F1-ATPase in the tumor mitochondria was found not to be very different from that in mitochondria of rat liver. Immunochemical determination of the amount of the natural ATPase inhibitor revealed that the tumor mitochondria contain 2-3-times more ATPase inhibitor than control mitochondria. It is concluded that the low ATPase activity of the tumor mitochondria results from the inhibition of the enzyme activity by the natural ATPase inhibitor.

Amino acid sequence of bovine heart coupling factor 6

The amino acid sequence of bovine heart mitochondrial coupling factor 6 (F6) has been determined by automated Edman degradation of the whole protein and derived peptides. Preparations based on heat precipitation and ethanol extraction showed allotypic variation at three positions while material further purified by HPLC yielded only one sequence that also differed by a Phe-Thr replacement at residue 62. The mature protein contains 76 amino acids with a calculated molecular weight of 9006 and a pI of approximately equal to 5, in good agreement with experimentally measured values. The charged amino acids are mainly clustered at the termini and in one section in the middle; these three polar segments are separated by two segments relatively rich in nonpolar residues. Chou-Fasman analysis suggests three stretches of alpha-helix coinciding (or within) the high-charge-density sequences with a single beta-turn at the first polar-nonpolar junction. Comparison of the F6 sequence with those of other proteins did not reveal any homologous structures.

Release of the inhibitory action of the natural ATPase inhibitor protein on the mitochondrial ATPase

The rate of ATP hydrolysis by submitochondrial particles prepared from bovine heart mitochondria in the presence of Mg2+ and ATP increases from a value of 0.4 mumol min-1 mg-1 to 6-7 mumol min-1 mg-1 upon incubation for 5-6 h at 38 degrees C. The increase in activity does not occur in particles that have been passed through a Sephadex column. The activation is prevented and partially reversed by ATP. This indicates that the increase in hydrolytic activity is due to abolition of the inhibitory action of the natural ATPase inhibitor protein of Pullman and Monroy [(1963) J. Biol. Chem. 238, 3762-3769]. At maximal activation approximately 50% of the inhibitor protein of the starting preparation remains in the particles as inferred from direct assay of inhibitor protein content and by its interaction with 125I-labeled antibodies directed against the inhibitor protein. The extent of the activation, which presumably is an index of the equilibrium between active and inactive enzymes, is strictly dependent on salts. The rate of the activation depends on the concentration of salts and is favored by alkaline pH. From results of experiments on the effect of temperature on the rate of activation of the ATPase, it was calculated that the activation energy, delta H not equal to and delta S not equal to of the process were 53.34 kJ/mol, 50.83 kJ/mol and -158.99 J mol-1 K-1, respectively. The data indicate that in its native inhibiting state, the interaction of the inhibitor protein with the enzyme involves electrostatic interactions. Also it is concluded that abolition of the inhibitory action of the protein on ATPase activity is not compulsorily linked to release of the protein into the water space.

Spermine binding to submitochondrial particles and activation of adenosine triphosphatase

Studies on the effects of polyamines on oligomycin-sensitive ATPase activity of ox heart submitochondrial particles showed that, of the polyamines tested, only spermine affected the enzyme activity. Spermine within the physiological concentration range increased the Vmax. of the enzyme, but the Km for ATP was virtually unaffected. Binding studies of [14C]spermine to submitochondrial particles, under the same conditions as used for the ATPase assay, showed that the spermine binds to submitochondrial particles in a co-operative way; Hill plots of the data gave a Hill coefficient of 2 and a Kd of 8 microM. When submitochondrial particles were treated with trypsin, ATPase was not stimulated by spermine and the amount of spermine bound concomitantly was drastically decreased. The ATPase activity of isolated F1-ATPase was not affected by spermine. Removal of the natural protein ATPase inhibitor did not suppress either the stimulation of the ATPase activity by spermine or the spermine binding to the particles. The results obtained suggested that the polyamine binds and acts at the level of the liaison between the coupling factor F1 and the membrane sector F0 of the ATPase complex.

Extraction of mitochondrial protein-lipid complexes into organic solvents: an approach to study the interaction between the ATPase and the mitochondrial ATPase-inhibitor protein

Protein-lipid complexes were transferred directly from mitochondria and submitochondrial particles into hexane and ether. The protein-lipid residue left after solvent removal from these extracts was used to form liposomes which display low-temperature-resistant ATPase activity. Centrifugation experiments indicate that the ATPase activity is associated to the vesicles. Most of the F1-ATPases appear to be accessible to the external water phase of the liposomes. The ATPase activity of these particles was insensitive to dicyclohexylcarbodiimide and oligomycin. Incubation of these vesicles at room temperature activated (4--10-fold) the ATPase through a process that is partially sensitive to phenylmethylsulfonyl fluoride. The results with purified ATPase-inhibitor protein and (F1--ATPase)-inhibitor complex indicate that the activation process in the liposomes is due to the abolition of the inhibitory action of the inhibitor protein bound to a large fraction of the extracted ATPases. Liposomes prepared from hexane extracts obtained from submitochondrial particles having different levels of ATPase activity displayed an activation ratio which correlated with the number of ATPases that are inhibited by the inhibitor protein in the submitochondrial particles. The extraction of mitochondrial ATPase and its incorporation into liposomes followed by activity measurements may be used to judge the number of ATPases that in a given preparation contain the inhibitor protein in its inhibiting site.

Isolation, characterization, and reconstitution of a solubilized fraction containing the hydrophobic sector of the mitochondrial proton pump

The hydrophobic sector of the mitochondrial ATPase complex was purified by sequential extraction with cholate and octylglucoside, by further differential solubilization with guanidine and cholate in the presence of phosphatidylcholine, and by fractionation with ammonium sulfate. A polypeptide with a mass of 28,000 dalton was present in the purified hydrophobic section which was cleaved by trypsin, resulting in loss of reconstitution activity. In contrast, dicyclohexylcarbodiimide-binding proteolipid remained unimpaired after exposure to trypsin. The 32Pi-ATP exchange activity of the reconstituted ATPase complex was inhibited by p-hydroxymercuribenzoate, which reacted primarily with the 28,000-dalton protein, as monitored by acrylamide gel electrophoresis with 14C-labeled inhibitor. The function of a 22,000-dalton polypeptide and of some minor components in the region of the proteolipid remains unknown. An examination of the phospholipid requirements for reconstitution of an active complex revealed an unexpected discrepancy. With an excess of phosphatidylethanolamine, optimal reconstitution of 32Pi-ATP exchange and ATP synthesis in the presence of bacteriorhodopsin and light was achieved: at a high phosphatidylcholine:phosphatidylethanolamine ratio, the rate of ATP synthesis remained high, but the rate of 32Pi-ATP exchange dropped precipitously. A new procedure is described for the reconstitution of the ATPase complex with purified phospholipids which is stable for at least 15 days.