Structure and function of H+-ATPase

The day/night proteome in the murine heart

Circadian rhythms are essential to cardiovascular health and disease. Temporal coordination of cardiac structure and function has focused primarily at the physiological and gene expression levels, but these analyses are invariably incomplete, not the least because proteins underlie many biological processes. The purpose of this study was to reveal the diurnal cardiac proteome and important contributions to cardiac function. The 24-h day-night murine cardiac proteome was assessed by two-dimensional difference in gel electrophoresis (2D-DIGE) and liquid chromatography-mass spectrometry. Daily variation was considerable, as ∼7.8% (90/1,147) of spots exhibited statistical changes at paired times across the 24-h light- (L) dark (D) cycle. JTK_CYCLE was used to investigate underlying diurnal rhythms in corresponding mRNA. We next revealed that disruption of the L:D cycle altered protein profiles and diurnal variation in cardiac function in Langendorff-perfused hearts, relative to the L:D cycle. To investigate the role of the circadian clock mechanism, we used cardiomyocyte clock mutant (CCM) mice. CCM myofilaments exhibited a loss of time-of-day-dependent maximal calcium-dependent ATP consumption, and altered phosphorylation rhythms. Moreover, the cardiac proteome was significantly altered in CCM hearts, especially enzymes regulating vital metabolic pathways. Lastly, we used a model of pressure overload cardiac hypertrophy to demonstrate the temporal proteome during heart disease. Our studies demonstrate that time of day plays a direct role in cardiac protein abundance and indicate a novel mechanistic contribution of circadian biology to cardiovascular structure and function.

Electrogenic proton transport by intercalated cells of tight urinary epithelia

Structure-function studies of the turtle bladder indicate that electrogenic proton secretion into the urinary compartment is accomplished by alpha-type intercalated cells which are rich in carbonic anhydrase. In the absence of electrochemical potential gradients (delta mu H = 0), the rate of H+ secretion (JH) is a function of the number of H+ pumps in position at the apical cell membrane, as judged from morphometric and freeze-fracture studies of apical membrane area characterized by a cytoplasmic coating with studs and by rod-shaped intramembrane particles (RSP). At a given pump population, JH is a sigmoid function of delta mu H, with delta pH and delta psi having equivalent effects on JH. The JH versus delta mu H relation reflects the intrinsic properties of the H+ pump and suggests a H+ pump model consisting of two components, a channel through the apical membrane across which delta mu H falls, and a catalytic unit located within the cytoplasm (outside of delta mu H). Each intramembrane RSP is associated with several cytoplasmic studs, but the precise relations between the two remain to be clarified.

Characterization of Mg2+-ATPase activity in isolated B16 murine melanoma melanosomes

B16 murine melanoma melanosomes were purified using sucrose density gradient centrifugation. ATPase activity was evaluated in presence of specific ATPase inhibitors, and compared with melanosome ATP-driven proton translocating activity in the melanosome. Mg2+ dependent ATPase activity was greatly inhibited (82%) by the specific inhibitors of vaculor proton translocating ATPase; Cis-didimethylsulfoxide dichloroplatinum (II) at approximately 90 microM and bafilomycin AI at two fold higher concentrations. Less inhibition, about 30 and 45% was obtained with N, N1-dicyclohexylcarbodiimide and N-ethylmaleimide, and the maximal effect occurred in the 50-100 microM and 0.1-1.5 mM ranges, respectively. These drugs at similar concentrations also inhibited the proton pumping activity to the same extent as observed for ATPase activity and half-maximal inhibition of each activity was found at nearly similar concentrations. Carbonylcyanide p-trifluoromethoxyphenyl hydra zone (FCCP) prevented ATP from setting up a pH gradient across the melanosomal membrane but stimulated Mg2+ ATPase activity significantly. Replacement of 5 mM Mg2+ with equimolar Ca2+ brought about a 60% inhibition in divalent cation-dependent ATPase- activity, and an 85% inactivation of ATP-linked melanosomal H+ pump activity. In the presence of optimal concentrations of Ca2+ and Mg2+ ATPase activity was similar to that seen in a Mg2+ medium. In Ca2+ medium ATPase activity was inhibited by CDDP and stimulated by FCCP, however these effects were two to three fold less than those observed in Mg2+ medium. FCCP failed to stimulate ATPase activity in CDDP- supplemented medium, thus suggesting that the same ATPase activity fraction was sensitive to both CDDP and FCCP. Mg2+-ATPase activity, like the proton-pump was anion dependent. The lowest activity was recorded in F medium, and increased in the order of F < So4(2-) < CL- = Br-. These results show that the ATPase activity may be related to the melanosomal proton pump.

When an ATPase is not an ATPase: at low temperatures the C-terminal domain of the ABC transporter CvaB is a GTPase

The ATP-binding cassette (ABC) transporters belong to a large superfamily of proteins which share a common function and a common nucleotide-binding domain. The CvaB protein from Escherichia coli is a member of the bacterial ABC exporter subfamily and is essential for the export of the peptide antibiotic colicin V. Here we report that, surprisingly, the CvaB carboxyl-terminal nucleotide-binding domain (BCTD) can be preferentially cross-linked to GTP but not to ATP at low temperatures. The cross-linking is Mg2+ and Mn2+ dependent. However, BCTD possesses similar GTPase and ATPase activities at 37 degrees C, with the same kinetic parameters and with similar responses to inhibitors. Moreover, a point mutation (D654H) in CvaB that completely abolishes colicin V secretion severely impairs both GTPase and ATPase activities in the corresponding BCTD, indicating that the two activities are from the same enzyme. Interestingly, hydrolysis activity of ATP is much more cold sensitive than that of GTP: BCTD possesses mainly GTP hydrolysis activity at 10 degrees C, consistent with the cross-linking results. These findings suggest a novel mechanism for an ABC protein-mediated transport with specificity for GTP hydrolysis.

ATP synthesis by the F0F1 ATP synthase from thermophilic Bacillus PS3 reconstituted into liposomes with bacteriorhodopsin. 1. Factors defining the optimal reconstitution of ATP synthases with bacteriorhodopsin

Optimal conditions for the reconstitution of bacteriorhodopsin and H+-transporting ATP synthase from thermophilic Bacillus PS3 (TF0F1) were determined. Phosphatidylcholine/phosphatidic acid liposomes prepared by reverse-phase evaporation were treated with various amounts of Triton X-100, octyl glucoside, octaethylene glycol n-dodecylether, sodium cholate or sodium deoxycholate and the incorporation of proteins by these detergents was studied at each step of the solubilization process. After removal of detergent by means of SM-2 Bio-Beads, the light-driven ATP synthase activities of the resulting proteoliposomes were analyzed at 40 degrees C. The nature of the detergent used for reconstitution was important for determining the mechanism of protein insertions. The most efficient reconstitutions were obtained with octyl glucoside or Triton X-100 by insertion of the proteins into detergent-saturated liposomes. The conditions for reconstitutions were further optimized with regard to functional coupling between bacteriorhodopsin and TF0F1. It was demonstrated that one of the main factors limiting the production of efficient reconstituted proteoliposomes was related to activation of the highly stable TFO-F1. Activation was accomplished by total solubilization of phospholipids and proteins in a Triton X-100/octyl glucoside mixture containing 20 mM octyl glucoside, leading to a threefold stimulation of the ATP synthase activity. Final ATP synthase activities depended greatly on the lipid/bacteriorhodopsin and the lipid/TF0F1 ratios as well as on the phospholipid used. In particular, light-driven ATP synthesis depended upon the presence of negatively charged phospholipids. Cholesterol was found to induce a fourfold increase in ATP synthase activity with a concomitant 65% decrease in the Km for ADP, suggesting that sterols can modulate catalytic events mediated by F1. Preparations obtained by this step-by-step reconstitution procedure displayed activities up to 20-fold higher (500-800 nmol ATP x min(-1) x mg TF0F1(-1) in the presence of cholesterol) than the maximal values reported in the literature for light-driven ATP synthesis TF0F1 measured under similar conditions. This study also allowed rationalization of the different parameters involved in reconstitution experiments and the present simple method is shown to be of general use for preparation of efficient proteoliposomes containing bacteriorhodopsin and choloroplast or mitochondrial F0F1-type ATP synthases.

A novel insertion sequence (IS)-like element of the thermophilic bacterium PS3 promotes expression of the alanine carrier protein-encoding gene

A novel insertion sequence (IS)-like element was found in the 5'-upstream region of the alanine carrier protein-encoding gene (acp) in the thermophilic bacterium PS3 chromosomal DNA. The sequence contained an open reading frame (ORF) encoding a polypeptide of 369 amino acids which revealed high similarity with ORFs from IS891 from the cyanobacterium Anabaena and IS1136 from Saccharopolyspora erythraea. The direction of transcription was the same as that of acp, and typical inverted and direct repeats characteristic of IS were found in both the 5' and 3' region of the ORF. Southern hybridization analysis of the chromosomal DNA revealed that multiple copies of the ORF sequence were contained in the PS3 genome. This element might well be a member of a new IS family including IS891 and IS1136, and we have designated this element IS1341. The analysis of acp expression in Escherichia coli cells indicated that IS1341 promotes the expression of acp.

ATP synthesis by the F0F1-ATPase from the thermophilic Bacillus PS3 co-reconstituted with bacteriorhodopsin into liposomes. Evidence for stimulation of ATP synthesis by ATP bound to a noncatalytic binding site

F-type ATPase from the thermophilic Bacillus PS3, TF0F1, which was essentially free of bound nucleotides after isolation and purification, was co-reconstituted into liposomes with the light-driven proton pump bacteriorhodopsin. The time course of the light-induced ATP synthesis was biphasic; an initial slow phase accelerated to a final steady-state rate two to three times faster. Adding ATP before initiating the reaction suppressed the slow phase, suggesting that the state of occupancy of specific sites by ATP regulated the synthetic activity of TF0F1. Incubating the purified TF0F1 with ADP and ATP revealed one ADP and two ATP binding sites that were stable to gel filtration. We analyzed the time courses of light-induced ATP synthesis for the enzyme with different nucleotide content, after co-reconstitution into liposomes with bacteriorhodopsin. The two ATP sites were identified to have regulatory function. A complex containing TF0F1.ADP, 1:1, was co-reconstituted with various quantities of ATP to obtain a range of molar ratios of TF0F1.ADP:ATP of between 1:0 and 1:1.7. It was found that the initial rate of ATP synthesis increased with the level of ATP bound to the enzyme. After binding one ATP, a stimulation of ATP synthesis by a factor of 2 was observed. The second ATP site also exhibited regulatory properties. It stimulated ATP synthesis but to a much smaller extent; the stimulation did not exceed 20%. Binding of the photoreactive analogues 2-azido-[alpha-32P]ADP and 2-azido-[alpha-32P]ATP to the TF0F1 and their effects on the rate of ATP synthesis are described further.(ABSTRACT TRUNCATED AT 250 WORDS)

Identification of two new genes in the Pseudomonas aeruginosa amidase operon, encoding an ATPase (AmiB) and a putative integral membrane protein (AmiS)

The nucleotide sequence of the amidase operon of Pseudomonas aeruginosa has been completed and two new genes identified amiB and amiS. The complete gene order for the operon is thus amiEBCRS. The amiB gene encodes a 42-kDa protein containing an ATP binding motif that shares extensive homology with the Clp family of proteins and also to an open reading frame adjacent to the amidase gene from Rhodococcus erythropolis. Deletion of the amiB gene has no apparent effect on inducible amidase expression and it is thus unlikely to encode a regulatory protein. A maltose-binding protein-AmiB fusion has been purified and shown to have an intrinsic ATPase activity (Km = 174 +/- 15 mM; Vmax = 2.4 +/- 0.1 mM/min/mg), which is effectively inhibited by ammonium vanadate and ADP. The amiS gene encodes an 18-kDa protein with a high content of hydrophobic residues. Hydropathy analysis suggests the presence of six transmembrane helices in this protein. The AmiS sequences is homologous to an open reading frame identified adjacent to the amidase gene from Mycobacterium smegmatis and to the ureI gene from the urease operon of Helicobacter pylori. AmiS and its homologs appear to be a novel family of integral membrane proteins. Together AmiB and AmiS resemble two components of an ABC transporter system.

Detection of different adenosine triphosphatases in human placental brush border membranes

The microvillous membrane of human placental syncytiotrophoblast cells contains a high ATPase activity. The purpose of this study was to characterize this activity and to investigate the presence of vacuolar type H+ ATPase in this membrane. Intact brush border membrane vesicles strongly hydrolyzed ATP, reflecting the presence of ATPase on the external side of the membrane. The ATPase activity was entirely Mg2+ dependent and increased with pH. At pH 7.5, Vmax was 31.0 +/- 1.7 mumol/mg/20 min and Km 0.18 +/- 0.03 mM ATP. Hydrolysis of ATP was not influenced by the presence of bicarbonate or alkaline phosphatase inhibitors, but at pH 8 it decreased by half following addition of 100 microM dicyclohexylcarbodiimide (DCCD). At pH 7.5, 1 mM N-ethylmaleimide (NEM) depressed this activity by less than 5%. Opening the membrane vesicles with 0.1% desoxycholate (DOC) or Triton-X neither revealed any additional ATPase activity nor altered the low sensitivity to NEM. Treatment of these membranes with 1% cholate decreased the ATPase activity by more than 70% and did not enhance the sensitivity of ATP hydrolysis to NEM. 10(-7) M Bafilomycin, which reduced by 56 +/- 9% the ATPase activity in dog kidney brush border membranes treated with 0.1% DOC, had no effect on placental brush border membranes subjected to the same procedure. Finally, neither immunocytochemical staining using monoclonal antibody to the M(r) 31000 subunit of V-type H+ ATPase, nor electron microscopic examination detected the presence of H(+) ATPase in placental membranes. In conclusion, the placental brush border membrane is the site of a strong "ecto" ATPase activity which is partially DCCD sensitive.(ABSTRACT TRUNCATED AT 250 WORDS)

Kinetic models of coupling between H+ and Na(+)-translocation and ATP synthesis/hydrolysis by F0F1-ATPases: can a cell utilize both delta mu H+ and delta mu Na+ for ATP synthesis under in vivo conditions using the same enzyme?

Kinetic models of the F0F1-ATPase able to transport H+ or/and Na+ ions are proposed. It is assumed that (i) H+ and Na+ compete for the same binding sites, (ii) ion translocation through F0 is coupled to the rate-limiting step of the F1-catalyzed reaction. The main characteristics of the dependences of ATP synthesis and hydrolysis rates on delta psi, delta pH, and delta pNa are predicted for various versions of the coupling model. The mechanism of the switchover from delta mu H(+)-dependent synthesis to the delta mu Na(+)-dependent one is demonstrated. It is shown that even with a drastic drop in delta mu H+, ATP hydrolysis by the proton mode of catalysis can be effectively inhibited by delta psi and delta pNa. The results obtained strongly support the possibility that the same F0F1-ATPase in bacterial cells can utilize both delta muH+ and delta muNa+ for ATP synthesis under in vivo conditions.

The alpha beta complexes of ATP synthase: the alpha 3 beta 3 oligomer and alpha 1 beta 1 protomer

The basic structures of the catalytic portion (F1, alpha 3 beta 3 gamma delta epsilon) of ATP synthase are the alpha 3 beta 3 hexamer (oligomer with cooperativity) and alpha 1 beta 1 heterodimer (protomer). These were reconstituted from the alpha and beta subunits of thermophilic F1 (TF1), and the alpha 3 beta 3 hexamer was crystallized. On electrophoresis, both the dimer and hexamer showed bands with ATPase activity. Using the dimer and hexamer, we studied the nucleotide-dependent rapid molecular dynamics. The formation of the hexamer required neither nucleotide nor Mg. The hexamer was dissociated into the dimer in the presence of MgADP, while the dimer was associated into the hexamer in the presence of MgATP. The hexamer, like mitochondrial F1 and TF1, showed two kinds of ATPase activity: one was cooperative and was inhibited by only one BzADP per hexamer, and the other was inhibited by three BzADP per hexamer.

ATPase activities in peroxisome-proliferating yeast

Preliminary studies on yeast peroxisomes have suggested that the membrane of these organelles may contain a proton-pumping ATPase. It has been reported that peroxisome-associated activity is similar to the F0-F1 mitochondrial type ATPase in its sensitivity to azide at pH 9.0, but characteristics of the plasma membrane type ATPase are also evident in peroxisomal preparations in that they exhibit pH 6.5 activity that is sensitive to vanadate. A comparative study of the prominent organellar ATPase activities was undertaken as a probe into the existence of an enzyme that is unique to the peroxisome, and biochemical properties of yeast mitochondrial, plasma membrane, together with peroxisomally-associated H(+)-ATPases are presented. Enzyme marker analysis of sucrose gradient fractions revealed a high degree of correlation between the amount of azide-sensitive pH 9.0 ATPase activity and that of the mitochondrial membrane marker, cytochrome c oxidase, in peroxisomal preparations. Purified mitochondrial and peroxisomally-associated activities were highly sensitive to the presence of sodium azide, N,N' -dicyclohexylcarbodiimide (DCCD) and venturicidin when measured at pH 9.0. Comparisons of peroxisomal activities with those of the purified plasma membrane at pH 6.0 in the presence of azide showed similar sensitivity profiles with respect to inhibitors of yeast plasma membrane ATPases such as vanadate and p-chloromercuriphenyl-sulfonic acid (CMP). Purified peroxisomal membranes, furthermore, reacted with antibody to the mitochondrial F1 subunit (as revealed by Western blot analysis), and [35S] methionine-labeled, glucose-grown cells processed with unlabeled methanol-grown cells, yielded sucrose gradient fractions that were radioactive in bands that were also recognized by F1 antibody. Isolated fractions in these experiments had similar ratios of cpm:pH 9.0 ATPase activities, suggesting that this activity is mitochondrial in origin. The data presented for the characteristics of the peroxisomally-associated activity strongly suggest that the majority of the ATPase activity found in peroxisomal preparations is derived from other organelles.

The F1-type ATPase in anaerobic Lactobacillus casei

An ATPase from anaerobic Lactobacillus casei has been isolated and 100-times purified. The 400 kDa enzyme molecule was found to have a hexagonal structure 10 nm in diameter composed of at least six protein masses. SDS-electrophoresis reveals four or, under certain conditions, five types of subunit, of apparent molecular masses 57 (alpha), 55 (beta), 40 (gamma), 22 (delta) and 14 (epsilon) kDa with stoichiometry of 3 alpha, 3 beta, gamma, delta, epsilon. The following features resembling F1-ATPases from other sources were found to be inherent in the solubilized L. casei ATPase. (i) Detachment from the membrane desensitizes ATPase to low DCCD concentrations and sensitizes it to water-soluble carbodiimide. (ii) Soluble ATPase is inhibited by Nbf chloride and azide, is resistant to SH-modifiers and is activated by sulfite and octyl glucoside, the activating effect being much stronger than in the case of the membrane-bound ATPase. Substrate specificity of the enzyme is also similar to that of other factors F1. Divalent cations strongly activate the soluble enzyme when added at a concentration equal to that of ATP. An excess of Mn2+, Mg2+ or Co2+ inhibits ATPase activity of F1, whereas that of Ca2+ induces its further activation. No other F1-like ATPases are found in L. casei. It is concluded that this anaerobic bacterium possesses a typical F1-ATPase similar to those in mitochondria, chloroplasts, aerobic and photosynthetic eubacteria.

Uncoupler-resistant mutants of bacteria

The chemiosmotic model of energy transduction offers a satisfying and widely confirmed understanding of the action of uncouplers on such processes as oxidative phosphorylation; the uncoupler, by facilitating the transmembrane movement of protons or other compensatory ions, reduces the electrochemical proton gradient that is posited as the energy intermediate for many kinds of bioenergetic work. In connection with this formulation, uncoupler-resistant mutants of bacteria that neither exclude nor inactivate these agents represent a bioenergetic puzzle. Uncoupler-resistant mutants of aerobic Bacillus species are, in fact, membrane lipid mutants with bioenergetic properties that are indeed challenging in connection with the chemiosmotic model. By contrast, uncoupler-resistant mutants of Escherichia coli probably exclude uncouplers, sometimes only under rather specific conditions. Related phenomena in eucaryotic and procaryotic systems, as well as various observations on uncouplers, decouplers, and certain other membrane-active agents, are also briefly considered.

Regulatory proteins of F1F0-ATPase: role of ATPase inhibitor

An intrinsic ATPase inhibitor inhibits the ATP-hydrolyzing activity of mitochondrial F1F0-ATPase and is released from its binding site on the enzyme upon energization of mitochondrial membranes to allow phosphorylation of ADP. The mitochondrial activity to synthesize ATP is not influenced by the absence of the inhibitor protein. The enzyme activity to hydrolyze ATP is induced by dissipation of the membrane potential in the absence of the inhibitor. Thus, the inhibitor is not responsible for oxidative phosphorylation, but acts only to inhibit ATP hydrolysis by F1F0-ATPase upon deenergization of mitochondrial membranes. The inhibitor protein forms a regulatory complex with two stabilizing factors, 9K and 15K proteins, which facilitate the binding of the inhibitor to F1F0-ATPase and stabilize the resultant inactivated enzyme. The 9K protein, having a sequence very similar to the inhibitor, binds directly to F1 in a manner similar to the inhibitor. The 15K protein binds to the F0 part and holds the inhibitor and the 9K protein on F1F0-ATPase even when one of them is detached from the F1 part.

Cytoplasmic pH in pulmonary macrophages: recovery from acid load is Na+ independent and NEM sensitive

The pulmonary macrophage plays a primary role in the immunological defense of the lung. Although many studies have been devoted to elucidation of its phagocytic and secretory functions, little is known of its membrane transport properties or of how it regulates intracellular pH (pHi). The purpose of this study, therefore, was to determine base-line pHi and the mechanism(s) by which the cell recovers pHi when challenged with an intracellular acid load. Through the use of the pH-sensitive fluorescent dye, 2,7-biscarboxyethyl-5(6)-carboxy-fluorescein (BCECF), base-line pHi was estimated to be 7.24 +/- 0.03. Cells were acidified by two methods, nigericin and weak acids, while recovery (dpHi/dt) was monitored. The rate of recovery was found to be independent of external Na+ and K+ and was insensitive to amiloride. Pretreatment with 4,4'-diiso-thiocyanatostilbene-2,2'-disulfonic acid, an inhibitor of Cl- -HCO3- exchange, was also without effect on recovery from an intracellular acid load in these cells, under nominally HCO3- -free conditions. In contrast, N-ethylmaleimide (NEM) and N,N'-dicyclohexylcarbodiimide, nonspecific inhibitors of proton adenosinetriphosphatases (ATPases), virtually abolished pHi recovery. Efflux of H+ equivalents by pulmonary macrophages was measured by techniques involving both pH stat titration and the effect on fluorescence of extracellular BCECF. Basal H+ extrusion was approximately 2.75 +/- 0.64 nmol H+.min-1.10(6) cells-1 and was enhanced to approximately 26.0 +/- 6.95 nmol H+.min-1.10(6) cells-1 in acid-loaded cell suspensions. The basal rate of H+ extrusion was reduced to approximately 0.84 +/- 0.31 nmol H+.min-1.10(6) cells-1 in the presence of 1 mM NEM. These results suggest that recovery of cytoplasmic pH from an intracellular acid load, as well as regulation of pHi, under the conditions examined, is not mediated by a Na+-H+ exchanger in these cells. Rather, the data are consistent with the presence of an H+-ATPase in the plasma membrane of pulmonary macrophages.

Resolution of ion translocating proteolipid subclasses active in bacterial calcification

Formation of calcium hydroxyapatite occurs on membrane surfaces via interaction of calcium, inorganic phosphate, phospholipids, calcifiable proteolipids, and ion flux to and from the nucleating site. Recently, this laboratory reported that proteolipids from the calcifying bacterium, Bacterionema matruchotti, act as an ionophore when reconstituted into bacteriorhodopsin-proteoliposomes. This ionophoric activity is blocked by [14C]dicyclohexylcarbodiimide ([14C]DCCD). SDS-PAGE shows that [14C]DCCD binds to a single band of Mr 8500. To determine whether proteins other than the [14C]DCCD-binding protein are involved, we examined the function of proteolipid species extracted by solvents of differing polarity. Proteolipids were isolated independently from chloroform:methanol (2:1) and chloroform:methanol:HCl (200:100:1) extracts of the bacteria by Sephadex LH-20 chromatography and were electrophoresed on 12.5% acrylamide gels. The chloroform:methanol extract contained a major hand at Mr 10,000 that was not present in gels of proteolipid isolated by acidified solvent. Proteolipids extracted in chloroform:methanol:HCl included a broad band at Mr 8500, which co-migrated with the [14C] DCCD-binding protein. The rate and extent of proton translocation were not altered when either proteolipid extract was added individually to bacteriorhodopsin proteoliposomes. However, when proteolipids isolated from the chloroform:methanol and chloroform:methanol:HCl extracts were combined, the rate and extent of translocation were increased. These data demonstrate that at least two proteolipid proteins are necessary for ionophoric activity, the Mr 10,000 protein isolated by chloroform:methanol 2:1 and the [14C]DCCD-binding protein requiring acidified solvent for extraction.

ATP synthases--structure of the F1-moiety and its relationship to function and mechanism

A great deal of progress has been made in understanding both the structure and the mechanism of F1-ATPase. The primary structure is now fully known for at least five species. Sequence comparison between chloroplast, photobacteria, aerobic bacteria, and mitochondrial representatives allow us to infer more general functional relationships and evolutionary trends. Although the F1 moiety is the most studied segment of the H+-ATPase complex, there is not a full understanding of the mechanism and regulation of its hydrolytic activity. The beta subunit is now known to contain one and probably two nucleotide binding domains, one of which is believed to be a catalytic site. Recently, two similar models have been proposed to attempt to describe the "active" part of the beta subunits. These models are mainly an attempt to use the structure of adenylate kinase to represent a more general working model for nucleotide binding phosphotransferases. Labelling experiments seem to indicate that several critical residues outside the region described by the "adenylate kinase" part of this model are also actively involved in the ATPase activity. New models will have to be introduced to include these regions. Finally, it seems that a consensus has been reached with regard to a broad acceptance of the asymmetric structure of the F1-moiety. In addition, recent experimental evidence points toward the presence of nonequivalent subunits to describe the functional activity of the F1-ATPase. A summary diagram of the conformational and binding states of the enzyme including the nonequivalent beta subunit is presented. Additional research is essential to establish the role of the minor subunits--and of the asymmetry they introduce in F1--on the physiological function of the enzyme.

Proton pump-linked Mg2+-ATPase activity in isolated rat liver lysosomes

ATPase activity in highly purified rat liver lysosome preparations was evaluated in the presence of other membrane cellular ATPase inhibitors, and compared with lysosome ATP-driven proton translocating activity. Replacement of 5 mM Mg2+ with equimolar Ca2+ brought about a 50% inhibition in divalent cation-dependent ATPase activity, and an 80% inactivation of ATP-linked lysosomal H+ pump activity. In the presence of optimal concentrations of Ca2+ and Mg2+, ATPase activity was similar to that seen in an Mg2+ medium. Mg2+-dependent ATPase activity was greatly inhibited (from 70 to 80%) by the platinum complexes; cis-didimethylsulfoxide dichloroplatinum(II) (CDDP) at approximately 90 microM and cis-diaminedichloroplatinum(II) at twofold higher concentrations. Less inhibition, about 30 and 45%, was obtained with N,N'-dicyclohexylcarbodiimide and N-ethylmaleimide, and the maximal effect occurred in the 50-100 microM and 0.1-1.5 mM ranges, respectively. The concentration dependence of inhibition by the above drugs was determined for both proton pumping and ATPase activities, and half-maximal inhibition concentration of each activity was found at nearly similar values. A micromolar concentration of carbonylcyanide p-trifluoromethoxyphenylhydrazone (FCCP) prevented ATP from setting up a pH gradient across the lysosomal membranes, but stimulated Mg2+-ATPase activity significantly. ATPase activity in Ca2+ medium was also inhibited by CDDP and stimulated by FCCP, but both effects were two- to threefold less than those observed in Mg2+ medium. FCCP failed to stimulate ATPase activity in a CDDP-supplemented medium, thus suggesting that the same ATPase activity fraction was sensitive to both CDDP and FCCP. Mg2+-ATPase activity, like the proton pump, was anion dependent. The lowest activity was recorded in a F-medium, and increased in the order of F- less than SO2-4 less than Cl- approximately equal to Br-. The CDDP-sensitive ATPase activity observed, supported by Mg2+ and less so by Ca2+, may be related to lysosome proton pump activity.

The definition of mitochondrial H+ ATPase assembly defects in mit- mutants of Saccharomyces cerevisiae with a monoclonal antibody to the enzyme complex as an assembly probe

mit- mutants with genetically defined mutations in the mitochondrial structural genes of the H+-ATPase membrane subunits 6, 8 and 9 were analysed to determine the H+-ATPase assembly defects that resulted as a consequence of the mutations. These include mutants which do not synthesize one of the membrane subunits and mutants which can synthesize these subunits, but in an altered form. Protein subunits which can still be assembled to the defective H+-ATPase in these mutants were determined by immunoprecipitation using a monoclonal antibody to the beta-subunit of the enzyme complex. The results suggest that the assembly pathway of the mitochondrially synthesized H+-ATPase subunits involves the sequential addition of subunits 9, 8 and 6 to a membrane-bound F1-sector. In addition to subunits of the F0- and F1-sectors, two other polypeptides (Mr = 18,000 and Mr = 25,000) are associated with the yeast H+-ATPase. These polypeptides were not observed in the immunoprecipitates obtained from mutants in which the F0-sector is not properly assembled.

Ion-translocating properties of calcifiable proteolipids

De novo formation of calcium hydroxyapatite in biological systems occurs on membrane surfaces through specific interactions of Ca, Pi, phospholipids, calcifiable proteolipids, and ion flux to and from the nucleating site. This paper reports an in vitro model demonstrating an ion transport function for calcifiable proteolipid. Bacterionema matruchotii proteolipid was incubated with a radiolabeled H+-channel inhibitor, 14C-dicyclohexyl-carbodiimide, and binding characterized by displacement studies with DCCD or ethyldimethylaminopropylcarbodiimide. A carboxyl binding site was suggested by displacement of DCCD by the nucleophile, glycine ethyl ester. The displacement studies indicated that proteolipid bound DCCD via carboxyl group interaction in a hydrophobic region of the protein. SDS-polyacrylamide gel electrophoresis showed that all label was associated with a single band of 8500 Mr. No non-specific binding of 14C-DCCD to phospholipids occurred, since all bound label was associated with protein following Sephadex LH-20 chromatography of crude proteolipid. Phospholipid liposomes were prepared containing bacteriorhodopsin and proteolipid or proteolipid-14C-DCCD, via cholate dialysis. Transmembrane pH changes established by the bacteriorhodopsin H+ pump were measured in the presence and absence of added proteolipid. Proteolipid had an effect similar to those of uncouplers such as tetraphenylboron. Both the rate and extent of proton translocation increased following addition of proteolipid to BR-liposomes. 14C-DCCD abolished the proteolipid-augmented ion transport. When tetraphenylboron was used to abolish the transmembrane electrical potential, calcifiable proteolipid did not augment proton transport.(ABSTRACT TRUNCATED AT 250 WORDS)

The insensitivity to uncouplers of testis mitochondrial ATPase

Albumin-free testis mitochondrial ATPase activity failed to be stimulated by either 2,4-dinitrophenol (DNP) or carbonyl cyanide rho-trifluoromethoxyphenylhydrazone (FCCP). DNP scarcely enhanced the state 4 respiration and mitochondria proved to be poorly coupled. When 1% bovine serum albumin was added to the isolation medium, DNP or FCCP stimulated ATPase nearly twofold and the dose-response curves for the uncouplers on the QO2 reached a plateau at five- to sixfold. The DNP coupling index (q) also showed a 30-40% improvement. A dose-response curve for oligomycin on the rate of [gamma-32P]ATP synthesis showed a stimulation of ATP synthase activity by 10-100 ng inhibitor/mg protein, suggesting a possible blockade of "open" F0 channels. In the albumin preparation oligomycin inhibited ATP synthesis in the range 10-100 ng/mg protein. Since testis ATPase is known to be loosely bound to the membrane, an effect of albumin, improving tightness in the interaction of the F1 and the F0 sectors of the ATPase, is suggested.

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

Images

Structure of the novel membrane-coating material in proton-secreting epithelial cells and identification as an H+ATPase

Specialized proton-secreting cells known collectively as mitochondria-rich cells are found in a variety of transporting epithelia, including the kidney collecting duct (intercalated cells) and toad and turtle urinary bladders. These cells contain a population of characteristic tubulovesicles that are believed to be involved in the shuttling of proton pumps (H+ATPase) to and from the plasma membrane. These transporting vesicles have a dense, studlike material coating the cytoplasmic face of their limiting membranes and similar studs are also found beneath parts of the plasma membrane. We have recently shown that this membrane coat does not contain clathrin. The present study was performed to determine the structure of this coat in rapidly frozen and freeze-dried tissue, and to determine whether the coat contains a major membrane protein transported by these vesicles, a proton pumping H+ATPase. The structure of the coat was examined in proton-secreting, mitochondria-rich cells from toad urinary bladder epithelium by rapidly freezing portions of apical membrane and associated cytoplasm that were sheared away from the remainder of the cell using polylysine-coated coverslips. Regions of the underside of these apical membranes as large as 0.2 micron2 were decorated by studlike projections that were arranged into regular hexagonal arrays. Individual studs had a diameter of 9.5 nm and appeared to be composed of multiple subunits arranged around a central depression, possibly representing a channel. The studs had a density of approximately 16,800 per micron2 of membrane. Similar arrays of studs were also found on vesicles trapped in the residual band of cytoplasm that remained attached to the underside of the plasma membrane, but none were seen in adjacent granular cells. To determine whether these arrays of studs contained H+ATPase molecules, we examined a preparation of affinity-purified bovine medullary H+ATPase, using the same technique, after incorporation of the protein eluted from a monoclonal antibody affinity column into phospholipid liposomes. The affinity-purified protein was shown to be capable of ATP-dependent acidification. In such preparations, large paracrystalline arrays of studs identical in appearance to those seen in situ were found. The dimensions of the studs as well as the number per square micrometer of membrane were identical to those of toad bladder mitochondria-rich cells: 9.5 nm in diameter, 16,770 per micron2 of membrane.(ABSTRACT TRUNCATED AT 400 WORDS)

Electron-microscopic studies on location of SH-groups in mitochondrial F1-ATPase using a ferritin label

A new approach has been suggested for electron-microscopic study of the structure of mitochondrial F1-ATPase based on ferritin labeling. By means of sequential treatment with 2-iminothiolane and Nbs2 we obtained a modified ferritin (NbsSPrCNH-Ft) able to react with SH-groups of proteins and to form conjugates in which the protein and ferritin are bound by disulfide bonds. An electron-microscopic investigation of the negatively stained preparations of mitochondrial F1-ATPase, preincubated with modified ferritin, revealed such enzyme-ferritin conjugates. In case of modified ferritin, containing 360 mol SH-groups per mol protein, and F1-ATPase, pretreated with N-ethylmaleimide and then with dithiothreitol, conjugates were obtained in which ferritin molecules are bound to several (as many as four) of the six protein masses, comprising a bilayer molecule of the enzyme. Taking into consideration the biochemical data on the location of accessible SH-groups (only in alpha, gamma or epsilon subunits), it is inferred from the results obtained that one of the protein masses is a complex between beta subunit and at least one of the minor subunits located partially on the molecule's external side. This indicates the nonequivalence of different copies of the major subunits. Averaged images of the particles of the F1-F0 complex from bovine heart mitochondria and bacteria Micrococcus lysodeicticus were obtained. It was found that F0 component is bound to two adjacent protein masses of the F1-ATPase molecule. It is suggested that this binding may be due the nonequivalency of single-type major subunits.

The tonoplast proton-translocating ATPase of higher plants as a third class of proton-pumps

Taken together, all the data reported recently in the literature suggest that tonoplast ATPase belongs to a new class of proton pumps. To date, the most studied system is the proton-pumping ATPase from the tonoplast of Hevea latex. Its main characteristics are presented. It resembles the mitochondrial ATPase in its specificity, its substrate affinity, and its sensitivity to different inhibitors. However, for some aspects, it resembles the plasma membrane system in its response to other inhibitors tested (quercetin for example). It differs from both ATPases in its sensitivity to nitrate as well as by its molecular structure, i.e. a complex exhibiting a least 4 or 5 polypeptides. These results favor the existence of a third class of proton pumps, intermediate between the F1F0-class and the E1E2-class.

An Escherichia coli mutant exhibiting temperature-sensitive ATP synthesis

A mutant strain SM434 (ttr-3) of Escherichia coli that exhibits a temperature-sensitive Unc(succinate-nonutilizing) phenotype was characterized. The mutant allele ttr-3 was not linked to the ilvA gene, but was complemented by Fill carrying 81 min-91 min of the E. coli chromosome. The mutant strain SM434 exhibited resistance to N,N'-dicyclohexylcarbodiimide (DCCD) and a temperature-sensitive phenotype at the level of ATP synthesis, compatible with that of cell growth. These findings indicate that the mutant strain SM434 could carry a mutation (ttr-3) in an unknown gene responsible for the energy-transduction system.

A chemically explicit model for the molecular mechanism of the F1F0 H+-ATPase/ATP synthases

A general hypothesis for the molecular mechanism of membrane transport based on current knowledge of protein structure and the nature of ligand-induced protein conformational changes has recently been proposed [Scarborough, G. A. (1985) Microbiol. Rev. 49, 214-231]. According to this hypothesis, the essential reaction undergone by all proteinaceous transport catalysts is a ligand-induced hinge-bending-type conformational change that results in the transposition of binding-site residues from access on one side of the membrane to access on the other side. Subsequent release and/or alteration of the ligand or ligands that induce the conformational change facilitates the converse conformational change, which returns the binding-site residues to their original position. With this simple cyclic ligand-dependent gating process as a central feature, biochemically orthodox mechanisms for virtually all known transporters are readily conceived. In this article, a chemically explicit model for the molecular mechanism of the F1F0 H+-ATPase/ATP synthases of mitochondria, bacteria, and chloroplasts, formulated within the guidelines of this general transport paradigm, is presented. At least three points of potential interest arise from this exercise. First, with the aid of the model, it is possible to visualize how energy transduction catalyzed by these enzymes might proceed, with no major events left unspecified. Second, explicit possibilities as to the molecular nature of electric field effects on the transport process are raised. And finally, it is shown that enzyme conformational changes, energy-dependent binding-affinity changes, and several other related phenomena as well, need not be taken as evidence of "action at a distance" or indirect energy coupling mechanisms, as is sometimes assumed, because such events are also integral features of the mechanism presented, even though all of the key reactions proposed for both ATP-driven proton translocation and proton translocation-driven ATP synthesis occur at the enzyme active site.

Current-voltage relationships for proton flow through the F0 sector of the ATP-synthase, carbonylcyanide-p-trifluoromethoxyphenylhydrazone or leak pathways in submitochondrial particles

Respiring submitochondrial particles from which the F1 sector of ATP-synthase was displaced generated a membrane potential in the range of 115-140 mV. Addition of oligomycin raised the membrane potential by approximately 40 mV. The lower membrane potential in particles with F1 displaced is attributed to partial dissipation of the proton electrochemical gradient as a consequence of proton flow through the open proton channels provided by the F0 sectors of the ATP-synthase. The characteristics of proton flow through the open F0 channels were studied by varying the rate of electron transport-driven proton translocation which permitted the establishment of a range of steady-state membrane potentials. Open F0 channels appeared to have a gated response to the membrane potential such that they were inoperative when the potential fell below approximately 110 mV. The membrane potential was measured as a function of respiratory rate in intact Mg-ATP submitochondrial particles that had been treated with low concentrations of the protonophore carbonylcyanide-p-trifluoromethoxyphenylhydrazone. In general a linear dependence of membrane potential upon respiratory rate was observed except at the lowest concentrations of protonophore and highest respiratory rates, presumably because the effect of the protonophore was then offset by an increased rate of proton translocation driven by the respiratory chain. The effect of increasing concentrations of carbonylcyanide-p-trifluoromethoxyphenylhydrazone on the membrane potential of respiring submitochondrial particles was studied. It was found that equal amounts of the protonophore lowered the membrane potential to a lesser extent at lower values of the membrane potential. Treatment of Mg-ATP submitochondrial particles with oligomycin slightly increased (by approximately 10 mV) the size of the respiration-dependent membrane potential, but did not alter the profile of membrane potential as a function of succinate oxidation rate. The latter was controlled by titration with malonate. This result indicates that the F0 sector of the ATP-synthase does not significantly contribute to leak pathways in intact submitochondrial particles.

Dicyclohexylcarbodiimide-sensitive ATPase in Halobacterium saccharovorum

Membranes from Halobacterium saccharovorum contained a cryptic ATPase which required Mg2+ or Mn2+ and was activated by Triton X-100. The optimal pH for ATP hydrolysis was 9-10. ATP or GTP were hydrolyzed at the same rate while ITP, CTP, and UTP were hydrolyzed at about half that rate. The products of ATP hydrolysis were ADP and phosphate. The ATPase required high concentrations (3.5 M) of NaCl for maximum activity. ADP was a competitive inhibitor of the activity, with an apparent Ki of 50 microM. Dicyclohexylcarbodiimide (DCCD) inhibited ATP hydrolysis. The inhibition was marginal at the optimum pH of the enzyme. When the ATPase was preincubated with DCCD at varying pH values, but assayed at the optimal pH for activity, DCCD inhibition was observed to increase with increasing acidity of the preincubation medium. DCCD inhibition was also dependent on time of preincubation, and protein and DCCD concentrations. When preincubated at pH 6.0 for 4 h at a protein:DCCD ratio of 40 (w/w), ATPase activity was inhibited 90%.

Photosynthetic ATPases: purification, properties, subunit isolation and function

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

Biogenesis of mitochondria: defective yeast H+-ATPase assembled in the absence of mitochondrial protein synthesis is membrane associated

We have investigated the extent to which the assembly of the cytoplasmically synthesized subunits of the H+-ATPase can proceed in a mtDNA-less (rho degree) strain of yeast, which is not capable of mitochondrial protein synthesis. Three of the membrane sector proteins of the yeast H+-ATPase are synthesized in the mitochondria, and it is important to determine whether the presence of these subunits is essential for the assembly of the imported subunits to the inner mitochondrial membrane. A monoclonal antibody against the cytoplasmically synthesized beta-subunit of the H+-ATPase was used to immunoprecipitate the assembled subunits of the enzyme complex. Our results indicate that the imported subunits of the H+-ATPase can be assembled in this mutant, into a defective complex which could be shown to be associated with the mitochondrial membrane by the analysis of the Arrhenius kinetics of the mutant mitochondrial ATPase activity.

Monoclonal antibodies against subunits of yeast mitochondrial H+-ATPase

Fourteen stable lines of myeloma-spleen cell hybrids producing antibodies against the mitochondrial H+-ATPase have been isolated. One reacted with the alpha-subunit of the enzyme complex (Mr 56000), nine with the beta-subunit (Mr 54000), and four with a 25 kDa subunit which has not been previously characterized. These antibodies are inhibitory or stimulatory or have no effect upon the enzyme activity. Two of the monoclonal anti-beta-subunit antibodies were found to be particularly effective in immunoprecipitating intact H+-ATPase complex.