Ultrastructural and cytochemical analysis of Na+, K+, ATPase and H+, K+, ATPase in parietal cells of gastric mucosa in the rabbit

Rabbit gastric secretion has the physiological peculiarity of being continuous and uninfluenced by food intake. In this respect, ultrastructural analysis of rabbit parietal cells has revealed morphofunctional features situated between states of rest and very active acid secretion. Our cytochemical study shows that Mg2+ ATPase and ADPase activities vary from cell to cell and can even be totally absent. These activities concern either microcanaliculi or laterobasal folds or both, but never tubulovesicles. Application of the technique of Mayahara to K+ pNPP, associated or not with inhibitors (ouabain, vanadate, N-ethyl-maleimide, sodium fluoride), enabled us to confirm the coexistence of H+, K+, ATPase and Na+, K+, ATPase activities in the rabbit and to determine that these activities concern basolateral folds, microcanaliculi, hyaloplasm and tubulovesicles. The global activity of K+, pNPPase varied considerably in intensity. The results of using inhibitors suggest that proton transport ceases completely in certain cells. The signs of functional alternation found in this study are in agreement with physiological data relative to this animal.

Sheep and other animals with ceroid-lipofuscinoses: their relevance to Batten disease

Distinct pathological and histopathological changes distinguish the ceroid-lipofuscinoses from other storage diseases of humans and animals. These various disease entities likely reflect a variety of mutations of the same gene, or mutations of different genes associated with metabolism of the same or similar substrates. The disease in sheep most closely resembles the juvenile human disease. In it 50% of the lipopigment consists of subunit c of mitochondrial ATP synthase while the remaining constituents are considered normal for a lysosomal derived cytosome. The same subunit c has been shown to be also stored in affected English Setter, Border Collie, and Tibetan Terrier dogs, the Devon cow, and in the late infantile and juvenile human forms of disease but not in the infantile form. Thus it gives a chemical unity to at least some members of the group and allows a major conceptual change in regard to further directions of research.

cDNA cloning for and preparation of antibodies against subunit d of H(+)-ATP synthase in rat mitochondria

The cDNA for subunit d of rat mitochondrial H(+)-ATP synthase was cloned from a brain cDNA library. The protein contains internally repeat structures that have sequences similar to those of other ATP-related proteins. The antibodies raised against the protein A-subunit d fusion protein expressed in E. coli specifically recognized only the protein in the mitochondria. The Na2 CO3 fractionation followed by immunoblotting analyses suggest that at least a part of the protein is inserted into the membrane.

H+ extrusion by an apical vacuolar-type H(+)-ATPase in rat renal proximal tubules

The activity of Na+/H(+)-exchange and H(+)-ATPase was measured in the absence of CO2/HCO3 by microfluorometry at the single cell level in rat proximal tubules (superficial S1/S2 segments) loaded with BCECF [2'7'-bis(carboxyethyl)5-6-carboxyfluorescein- acetoxymethylester]. Intracellular pH (pHi) was lowered by a NH4Cl-prepulse technique. In the absence of Na+ in the superfusion solutions, pHi recovered from the acid load by a mechanism inhibited by 0.1 microM bafilomycin A1, a specific inhibitor of a vacuolar-type H(+)-ATPase. Readdition of Na+ in the presence of bafilomycin A1 produced an immediate recovery of pHi by a mechanism sensitive to the addition of 10 microM EIPA (ethylisopropylamiloride), a specific inhibitor of Na+/H+ exchange. The transport rate of the H(+)-ATPase is about 40% of Na+/H(+)-exchange activity at a similar pHi (0.218 +/- 0.028 vs. 0.507 +/- 0.056 pH unit/min. Pre-exposure of the tubules to 30 mM fructose, 0.5 mM iodoacetate and 1 mM KCN (to deplete intracellular ATP) prevented a pHi recovery in Na(+)-free media; readdition of Na+ led to an immediate pHi recovery. Tubules pre-exposed to Cl(-)-free media for 2 hr also reduced the rate of Na(+)-independent pHi recovery. In free-flow electrophoretic separations of brush border membranes and basolateral membranes, a bafilomycin A1-sensitive ATPase activity was found to be associated with the brush border membrane fraction; half maximal inhibition is at 6 x 10(-10) M bafilomycin A1.(ABSTRACT TRUNCATED AT 250 WORDS)

The osteoclast as a unicellular proton-transporting epithelium

Osteoclasts dissolve bone mineral by the vectorial secretion of hydrogen ion at their osseous attachment site. To accomplish this, the osteoclast employs a vacuolar H+ ATPase that is polarized to the specialized proton-secreting plasma membrane domain, the ruffled border. Physiologically and biochemically, they resemble the specialized proton-secreting intercalated cells of the renal collecting duct, which also use a polarized vacuolar H+ ATPase to effect transepithelial hydrogen ion transport. Studies on the mechanism of hydrogen ion transport by the kidney may therefore provide insights into the control of acid secretion by the osteoclast.

Dimorphism-associated changes in plasma membrane H(+)-ATPase activity of Candida albicans

In situ plasma membrane H(+)-ATPase activity was monitored during pH-regulated dimorphism of Candida albicans using permeabilized cells. ATPase activity was found to increase in both the bud and germ tube forming populations at 135 min which coincides with the time of evagination. Upon reaching the terminal phenotype the mycelial form exhibited higher H(+)-ATPase activity as compared to the yeast form. At the time of evagination H(+)-efflux exhibited an increase. K+ depletion resulted in attenuated ATPase activity and glucose induced H(+)-efflux. The results demonstrate that ATPase may play a regulatory role in dimorphism of C. albicans and K+ acts as a modulator.

Identification of the membrane-embedded regions of the Neurospora crassa plasma membrane H(+)-ATPase

Reconstituted proteoliposomes containing functional Neurospora crassa plasma membrane H(+)-ATPase molecules oriented predominantly with their cytoplasmic surface exposed were treated with trypsin and then subjected to Sepharose CL-6B column chromatography to remove the liberated peptides. The peptides remaining associated with the liposomes were then separated from the phospholipid by Sephadex LH-60 column chromatography and analyzed by sodium dodecyl sulfate-polyacrylamide gel electrophoresis. Six H(+)-ATPase peptides with approximate molecular masses of 7, 7.5, 8, 10, 14, and 21 kDa were found to be tightly associated with the liposomal membrane. Amino acid sequencing of the 7-, 7.5-, and 21-kDa peptides in the LH-60 eluate identified them as H(+)-ATPase fragments beginning at residues 99 or 100, 272, and 660, respectively. After further purification, the approximately 10- and 14-kDa peptides were also similarly identified as beginning at residues 272 and 660. The approximately 8-kDa fragment was purified further but could not be sequenced, presumably indicating NH2-terminal blockage. To identify which of the liposome-associated peptides are embedded in the membrane, H(+)-ATPase molecules in the proteoliposomes were labeled from the hydrophobic membrane interior with 3-(trifluoromethyl)-3-(m-[125I]iodophenyl)diazirine and cleaved with trypsin, after which the membrane-associated peptides were purified and assessed for the presence of label. The results indicate that the approximately 7-, 7.5-, and 21-kDa peptides are in contact with the lipid bilayer whereas the approximately 8-kDa peptide is not. Taken together with the results of our recent analyses of the peptides released from the proteoliposomes, this information establishes the transmembrane topography of nearly all of the 919 residues in the H(+)-ATPase molecule.

Expression and distribution of renal vacuolar proton-translocating adenosine triphosphatase in response to chronic acid and alkali loads in the rat

Renal hydrogen ion excretion increases with chronic acid loads and decreases with alkali loads. We examined the mechanism of adaptation by analyzing vacuolar proton-translocating adenosine triphosphatase (H+ ATPase) 31-kD subunit protein and mRNA levels, and immunocytochemical distribution in kidneys from rats subjected to acid or alkali loads for 1, 3, 5, 7, and 14 d. Acid- and alkali-loaded rats exhibited adaptive responses in acid excretion, but showed no significant changes in H+ ATPase protein or mRNA levels in either cortex or medulla. In contrast, there were profound adaptive changes in the immunocytochemical distribution of H+ ATPase in collecting duct intercalated cells. In the medulla, H+ ATPase staining in acid-loaded rats shifted from cytoplasmic vesicles to plasma membrane, whereas in alkali-loaded rats, cytoplasmic vesicle staining was enhanced, and staining of plasma membrane disappeared. In the cortical collecting tubule, acid loading increased the number of intercalated cells showing enhanced apical H+ ATPase staining and decreased the number of cells with basolateral or poorly polarized apical staining. The results indicate that both medulla and cortex participate in the adaptive response to acid and alkali loading by changing the steady-state distribution of H+ ATPase, employing mechanisms that do not necessitate postulating interconversion of intercalated cells with opposing polarities.

A potential role for guanine nucleotide-binding protein in the regulation of endosomal proton transport

The effects of guanosine 5'-triphosphate (GTP) and GTP-gamma-S, known activators of GTP binding proteins, on proton transport were investigated in endosome-enriched vesicles (endosomes). Endosomes were prepared from rabbit renal cortex following the intravenous injection of FITC-dextran. The rate of intravesicular acidification was determined by measuring changes in fluorescence of FITC-dextran. Both GTP and GTP-gamma-S stimulated significantly the initial rate of proton transport. In contrast, GDP-beta-S, which does not activate GTP binding proteins, inhibited proton transport. The rank order of stimulation was GTP-gamma-S greater than GTP greater than control greater than GDP-beta-S. GTP-gamma-S stimulation of proton transport was also observed under conditions in which chloride entry was eliminated, i.e., 0 mM external chloride concentration in the presence of potassium/valinomycin voltage clamping. GTP-gamma-S did not affect proton leak in endosomes as determined by collapse of H+ ATPase-generated pH gradients. ADP ribosylation by treatment of endosomal membranes with pertussis toxin revealed two substrates corresponding to the 39-41 kD region and comigrating with alpha i subunits. Pretreatment of the membranes with pertussis toxin had no effect on proton transport in the absence of GTP or GTP-gamma-S. However, pretreatment with pertussis toxin blocked the stimulation of proton transport by GTP. In contrast, as reported in other membranes by others previously, pertussis toxin did not prevent the stimulation of proton transport by GTP-gamma-S. These findings, taken together, indicate that GTP binding proteins are present in endosomal membranes derived from renal cortex and that activation of G protein by GTP and GTP-gamma-S stimulates proton transport in a rank order identical to that reported for other transport pathways modulated by Gi proteins. Therefore, these studies suggest that G proteins are capable of stimulating the vacuolar H ATPase of endosomes directly.

Vacuolar acidification and bafilomycin-sensitive proton translocating ATPase in human epidermal Langerhans cells

Langerhans cells (LC) are the principal antigen-presenting cells (APC) of squamous epithelia. We have previously shown that freshly isolated LC (fLC) are able to deliver endocytosed membrane MHC class II molecules into acidic environments, and that this capacity is lost when LC are placed in culture (cLC). Inasmuch as processing of antigens requires their passage through acidic compartments, we undertook the present study to examine the ability of fLC and cLC to take up acridine orange, and to identify proton-translocating ATPases in these cells. Using flow cytometry and fluorescence microscopy, acridine orange was observed to accumulate in acidic compartments in both fLC and cLC. Using a radioactive ATPase assay, crude membrane preparations from both fLC and cLC were shown to possess three types of ion-translocating ATPase, based on sensitivity to the following inhibitors: ouabain (Na+, K+ ATPase), oligomycin (mitochondrial F1F0 ATPase), and bafilomycin (vacuolar-type proton pump ATPase); the last type is responsible for acidification in vacuolar compartments. cLC displayed markedly less (less than 50%) total ATPase activity compared to fLC; however, the relative proportions of specific ATPases were similar in fLC and cLC. Combined use of the three inhibitors resulted in abrogation of only 25-40% of the total ATPase activity. Finally, treatment of LC with bafilomycin inhibited both acridine orange uptake and acidification of internalized HLA-DR molecules. These results confirm the ability of both fLC and cLC to acidify vacuolar compartments, thereby suggesting that lack of acidification of endocytosed membrane class II molecules in cultured cells is due to alternative routing to non-acidic organelles.

Colocalization of H(+)-ATPase and band 3 anion exchanger in rabbit collecting duct intercalated cells

Two major types of intercalated cells (IC) have been previously defined in rabbit collecting duct: alpha-cells have a basolateral band 3-like anion exchanger and secrete H+, whereas beta-cells bind peanut agglutinin (PNA) apically and are believed to secrete HCO3-. To further define IC types, we double-labeled kidney sections with anti-H(+) -ATPase antibodies and with either an anti-band 3 antibody or PNA. We found four patterns of staining: 1) IC with apical H(+)-ATPase and basal band 3, a configuration consistent with ongoing H+ secretion, which prevailed in the inner stripe of outer medulla (OMCDi); 2) diffuse H(+)-ATPase labeling across the cell and basal band 3, which was most numerous in the outer stripe of outer medulla (OMCDo); 3) IC with "bright" apical peanut lectin, diffuse H(+)-ATPase, and no band 3, which was abundant in the cortical collecting duct (CCD) and probably represents HCO3(-)-secreting cells; and 4) "hybrid" cells with various staining combinations (e.g., apical lectin binding and apical H(+)-ATPase), which although they are uncommon, were seen in the CCD. Consistent with this immunocytochemical finding of hybrid cells, cell-sorting studies on isolated CCD IC showed that 6-18% of PNA-positive cells also stained positively for band 3. We conclude that 1) band 3-positive IC in the OMCD vary axially. Most OMCDi IC are probably active proton secretors, whereas up to one-half of OMCDo IC may be latent H+ secretors. 2) The diffuse H(+)-ATPase pattern in putative beta-cells differs from comparable results in the rat and is not consistent with a "reversed" alpha-cell. HCO3- secretion by beta-cells may be driven by an H+ extrusion mechanism other than the alpha-cell pump re-sorted to the basolateral membrane. 3) The possibility of hybrid cells that might combine alpha- and beta-cell transport proteins suggests a mechanism for functional reversal of collecting duct IC polarity.

Domains of yeast plasma membrane and ATPase-associated glycoprotein

In yeast homogenates the plasma membrane H(+)-ATPase and a major surface glycoprotein of about 115 kDa are present in two membrane fractions with peak densities in sucrose gradients of 1.17 and 1.22. Immunogold electron microscopy of frozen yeast sections indicates that the ATPase is exclusively (greater than 95%) present at the surface membrane. Therefore the two ATPase-containing fractions appear to correspond to different domains of the plasma membrane. The 115 kDa glycoprotein is tightly associated with the ATPase during solubilization and purification of the enzyme. However, in a mutant lacking the glycoprotein the activity of the plasma membrane H(+)-ATPase is similar to wild type, suggesting that this association is fortuitous. The ATPase and the glycoprotein are difficult to separate by electrophoresis and therefore binding of concanavalin A to the ATPase cannot be unambiguously demonstrated in wild-type yeast. By utilizing the mutant without glycoprotein it was shown that the ATPase band of 105 kDa binds concanavalin A.

Localization of the plasma membrane and mitochondrial H(+)-ATPases in Leishmania donovani promastigotes

Immunochemical methods were used to characterize the proton-translocating ATPases (H(+)-ATPases) of the plasma membrane and mitochrondrion of Leishmania donovani promastigotes. Antisera directed against the plasma membrane H(+)-ATPase of Saccharomyces cerevisiae reacted with a 66 kDa membrane protein of L. donovani promastigotes. By immunocytochemistry, the antiserum was shown to label the cell and flagellar surface of promastigotes as well as the Golgi apparatus and the membrane of intracellular organelles. The target antigen was shown to possess ATPase activity resembling the leishmanial H(+)-ATPase activity. Antisera raised against the beta-subunit of the F0F1-ATPase of Escherichia coli reacted with a 56 kDa protein in L. donovani promastigotes. Ultrastructurally, the anti-beta-subunit antibody was exclusively associated with the mitochondrion in these cells. This antiserum immunoprecipitates ATP hydrolytic activity typical of the F1 beta-subunit activity of the mitochondria of higher eukaryotes.

Distribution and structure of the vacuolar H+ ATPase in endosomes and lysosomes from LLC-PK1 cells

Vacuolar proton pumps acidify several intracellular membrane compartments in the endocytic pathway. We have examined the distribution of the vacuolar H+ ATPase in LLC-PK1 cells and the structure of the biosynthetically labeled enzyme in membrane fractions enriched for endosomes or lysosomes. LLC-PK1 cells were allowed to internalize cytochrome c-coated colloidal gold as a marker for endocytic compartments. Proton pumps were identified in these cells by staining the cells with a monoclonal antibody against the vacuolar pump detected with either immunogold or immunoperoxidase techniques. H+ ATPase labeling was seen on structures resembling endosomes and lysosomes, but not on Golgi or plasma membrane. To examine the structure of the H+ ATPase in these compartments, we labeled LLC-PK1 cells for 24 h with [35S]methionine and used a Percoll gradient to obtain fractions enriched for endosomes or lysosomes. H+ ATPase immunoprecipitated from both fractions with monoclonal anti-H+ ATPase antibodies had labeled polypeptides of 70, 56, and 31 kDa. On two-dimensional gels, a comparison of the H+ ATPase from the endosomal and lysosomal fractions revealed that the 70-, 56-, and 31-kDa subunits were similar in both fractions. The results show that the vacuolar H+ ATPase in these cells is distributed primarily in endosomes and lysosomes and that the structure of the enzyme is similar in both compartments.

Sequential expression of phenotype markers for osteoclasts during differentiation of precursors for multinucleated cells formed in long-term human marrow cultures

Long-term human marrow cultures form multi-nucleated cells (MNC) which express the osteoclast phenotype. Mononuclear precursors for these MNC can be identified and highly enriched. We tested early (bipotent) and late (unipotent) precursors of these MNC for expression of several osteoclast differentiation markers: 1) the osteoclast vitronectin receptor, identified by the 23c6 monoclonal antibody, 2) the vacuolar-type proton pump, identified by the E11 monoclonal antibody, and 3) the calcitonin (CT) receptor, by autoradiography with 125I-labeled salmon calcitonin. We wished to determine if the proton pump was expressed in cells in long term marrow cultures and if its expression correlated with expression of the CT receptor and the vitronectin receptor. About 30% of early precursor cells reacted with the 23c6 monoclonal antibody, but none expressed CT receptors or showed amplified proton pump expression. The CT receptor and amplified proton pump expression were detected first on the late precursor, a stage in which every cell reacted strongly with the 23c6 monoclonal antibody. Over 80% of MNC formed from these late precursors expressed abundant CT receptors, and all MNC expressed the vitronectin receptor and showed amplified proton pump expression. In contrast, macrophage polykaryons and mononuclear macrophages formed in vitro failed to express the osteoclast vitronectin and CT receptors and expressed the proton pump at levels indistinguishable from those of surrounding cells.

Immunological detection of the mitochondrial F1-ATPase alpha subunit in the matrix of rat liver peroxisomes. A protein involved in organelle biogenesis?

Rat liver peroxisomes contain in their matrix the alpha-subunit of the mitochondrial F1-ATPase complex. The identification of this protein in liver peroxisomes has been achieved by immunoelectron microscopy and subcellular fractionation. No beta-subunit of the mitochondrial F1-ATPase complex was detected in the peroxisomal fractions obtained in sucrose gradients or in Nycodenz pelletted peroxisomes. The consensus peroxisomal targeting sequence (Ala-Lys-Leu) is found at the carboxy terminus of the mature alpha-subunit from bovine heart and rat liver mitochondria. Due to the dual subcellular localization of the alpha-subunit and to the structural homologies that exist between this protein and molecular chaperones [(1990) Biol. Chem. 265, 7713-7716] it is suggested that the protein should perform another functional role(s) in both organelles, plus to its characteristic involvement in the regulation of mitochondrial ATPase activity.

Evidence for the presence of a proton pump of the vacuolar H(+)-ATPase type in the ruffled borders of osteoclasts

Microsomal membrane vesicles prepared either from chicken medullary bone or isolated osteoclasts were shown to have ATP-dependent H(+)-transport activity. This activity was N-ethylmaleimide-sensitive but resistant to oligomycin and orthovanadate, suggesting a vacuolar-type ATPase. Furthermore, immunological cross-reactivity of 60- and 70-kD osteoclast membrane antigens with Neurospora crassa vacuolar ATPase was observed when analyzed by immunoblotting. Same antibodies labeled only osteoclasts in chicken and rat bone in immunohistochemistry. Immunoelectronmicroscopy localized these antigens in apical membranes of rat osteoclasts and kidney intercalated cells of inner stripe of outer medulla. Pretreatment of animals with parathyroid hormone enhanced the immunoreaction in the apical membranes of osteoclasts. No immunoreaction was seen in osteoclasts when antibodies against gastric H+,K(+)-ATPase were used. These results suggest that osteoclast resorbs bone by secreting protons through vacuolar H(+)-ATPase.

Endocytic vesicles from renal papilla which retrieve the vasopressin-sensitive water channel do not contain a functional H+ ATPase

The water permeability of the kidney collecting duct epithelium is regulated by vasopressin (VP)-induced recycling of water channels between an intracellular vesicular compartment and the plasma membrane of principal cells. To test whether the water channels pass through an acidic endosomal compartment during the endocytic portion of this pathway, we measured ATP-dependent acidification of FITC-dextran-labeled endosomes in isolated microsomal fractions from different regions of Brattleboro rat kidneys. Both VP-deficient controls and rat treated with exogenous VP were examined. ATP-dependent acidification was not detectable in endosomes containing water channels from distal papilla (osmotic water permeability Pf = 0.038 +/- 0.004 cm/s). In contrast, the addition of ATP resulted in a strong acidification of renal cortical endosomes (pHmin = 5.8, initial rate = 0.18-0.25 pH U/s). Acidification of cortical endosomes was reversed with nigericin and strongly inhibited by N-ethyl-maleimide. Passive proton permeability was similar and low in both cortical and papillary endosomes from rats treated or not treated with VP. The fraction of labeled endosomes present in microsomal preparations was determined by fluorescence imaging microscopy of microsomes nonspecifically bound to poly-l-lysine-coated coverslips and was 25% in cortical preparations compared to 14% (+VP) and 9% (-VP) in papillary preparations. The fraction of cortical endosomes was enriched 1.5-fold by immunoabsorption to coverslips coated with mAbs against the bovine vacuolar proton pump. In contrast, the fraction of papillary endosomes was depleted more than twofold by immunoabsorption to identical coverslips. Finally, sections of distal papilla stained with antibodies against the lysosomal glycoprotein LGP120 showed that most of the entrapped FITC-dextran did not colocalize with this lysosomal protein. These results demonstrate that vesicles which internalize water channels in kidney collecting duct principal cells lack functional proton pumps, and do not deliver the bulk of their FITC-dextran content to lysosomes. The data suggest that the principal cell contains a specialized nonacidic apical endocytic compartment which functions primarily to recycle membrane components, including water channels, to the plasma membrane.

Catalytic and regulatory sites of yeast plasma membrane H(+)-ATPase studied by directed mutagenesis

More than 35 site-directed mutants of the plasma membrane H(+)-ATPase of the yeast Saccharomyces cerevisiae have been constructed and expressed to investigate the function of N- and C-termini and of conserved amino acids. Conserved motif TGES seems to form part of both the catalytic machinery for the hydrolysis of the phosphorylated intermediate and the vanadate binding site. In addition, it is involved in the coupling of ATP hydrolysis to H+ transport. The phosphorylated intermediate is also essential for this coupling, but not for ATP hydrolysis. The aspartate residues of conserved motifs DPPR, TGD and TGDGVND (the last one) seem to form part of the ATP binding site. The positive charge of the conserved motif KGAP is important for the kinase or phosphorylating activity. A conserved proline and a conserved aspartate predicted to have a transmembrane location are essential for activity. The N-terminus contains a conserved acidic region which may be involved in assembly into the plasma membrane. All the hydrophobic stretches at the C-terminus are also required for assembly. The last 11 amino acids constitute a non-essential inhibitory domain involved in regulation of the enzyme by glucose metabolism.

The effect of prenylamine and organic nitrates on the bioenergetics of bovine catecholamine storage vesicles

We have compared the cardioprotective agents prenylamine and glyceryl trinitrate (GTN) with respect to their effects on the bioenergetics of catecholamine storage vesicles. Chromaffin granule ghosts, which have a well preserved ability to actively transport and store catecholamines, were used as a model for adrenergic synaptic vesicles due to their functional similarity. Prenylamine, which partially and reversibly deplete the endogenous stores of noradrenaline in adrenergic nerves and ganglia, was found to inhibit the generation of the transmembrane proton electrochemical gradient driven by a H(+)-ATPase, mainly by acting as an uncoupler of this ATPase. The inhibition of the energy dependent dopamine uptake (and noradrenaline biosynthesis) by prenylamine could be accounted for by its effect on the bioenergetics of the storage vesicles. The organic nitrates glyceryl trinitrate and isosorbide dinitrate also partly inhibited the catecholamine uptake in parallel with their effects on the proton electrochemical gradient. It is concluded that GTN is a weak catecholamine depletor. Experiments with 3-morpholinosydnonimin-hydrochloride, a source of nitric oxide (NO), opens up the possibility that the mechanism of inhibition of the bioenergetics of chromaffin granule ghosts by GTN is mediated by NO.

cDNA cloning and sequencing for the import precursor of subunit B in H(+)-ATP synthase from rat mitochondria

The nucleotide sequence of the import precursor of subunit b of rat liver H(+)-ATP synthase has been determined from a recombinant cDNA clone isolated by screening a rat liver cDNA library with a probe DNA. The sequence was composed of 1,124 nucleotides including a coding region for the import precursor of subunit b and noncoding regions of both the 5'- and 3'-sides. The import precursor of subunit b and its mature polypeptide deduced from the open reading frame consisted of 256 and 214 amino acid residues with a molecular weight of 28,867 and 24,628, respectively. The presequence of 42 amino acids could be the import signal peptide which serves to direct the protein into the mitochondrial matrix.

The H(+)-ATPase of the plasma membrane from yeast. Kinetics of ATP hydrolysis in native membranes, isolated and reconstituted enzymes

The H(+)-ATPase of the plasma membrane from Saccharomyces cerevisiae has been isolated, purified and reconstituted into asolectin liposomes. The kinetics of ATP hydrolysis have been compared for the H(+)-ATPase in the plasma membrane, in a protein/lipid/detergent micelle (isolated enzyme) and in asolectin proteoliposomes (reconstituted enzyme). In all three cases the kinetics of ATP hydrolysis can be described by Michaelis-Menten kinetics with Km = 0.2 mM MgATP (plasma membranes), Km = 2.4 mM MgATP (isolated enzyme) and Km = 0.2 mM MgATP (reconstituted enzyme). However, the maximal turnover decreases only by a factor of two during isolation of the enzyme and does not change during reconstitution; the activation of the H(+)-ATPase by free Mg2+ is also only slightly influenced by the detergent. The dissociation constant of the enzyme-Mg2+ complex Ka, does not alter during isolation and the dissociation constant of the enzyme-substrate complex, Ks, increases from Ks = 30 microM (plasma membranes) to Ks = 90 microM (isolated enzyme). ATP binding to the H(+)-ATPase ('single turnover' conditions) for the isolated and the reconstituted enzyme resulted in both cases in a second-order rate constant k1 = 2.6 x 10(4) M-1.s-1. From these observations it is concluded that the detergent used (Zwittergent TM 3-14) interacts reversibly with the H(+)-ATPase and that practically all H(+)-ATPase molecules are reconstituted into the liposomes with the ATP-binding site being directed to the outside of the vesicle.

Stoichiometry of chargerin II (A6L) in the H(+)-ATP synthase of rat liver mitochondria

Previous studies suggested that the hydrophobic protein chargerin II, which is encoded in the A6L of mitochondrial DNA, may have a key role in the energy transduction by mitochondrial H(+)-ATP synthase because an antibody against chargerin II inhibited ATP synthesis and ATP-Pi exchange, in an energy-dependent fashion. In the present work, the contents of chargerin II in the H(+)-ATP synthase purified from rat liver mitochondria and in submitochondrial particles were determined by radioimmunoassay. Results showed that the H(+)-ATP synthase contained chargerin II in a molar ratio of one to one. This is the first report on the stoichiometry of the A6L-product in mitochondrial H(+)-ATP synthase.

Rotational dynamics of chloroplast ATP synthase in phospholipid vesicles

The rotational dynamics of the purified dicyclohexylcarbodiimide-sensitive H(+)-ATPase (DSA) reconstituted into phospholipid vesicles and of the DSA coreconstituted with the proton pump bacterio-rhodopsin were examined by using the technique of time-resolved phosphorescence emission anisotrophy. The phosphorescent probe erythrosin isothiocyanate was used to covalently label the gamma-polypeptide of DSA before reconstitution. Rotational correlation times were measured under a variety of conditions. The rotational correlation time was independent of the viscosity of the external medium but increased significantly as the microviscosity of the membrane increased. This indicates the rotational correlation times are a measure of the enzyme motion within the membrane. The activation energy associated with the rotational correlation time is 8-10 kcal/mol. At 4 degrees C, the correlation time, typically approximately 100-180 microseconds, was unaffected by the addition of substrates and the presence of a membrane pH gradient. Therefore, molecular rotation of the DSA does not appear to play an important role in enzyme catalysis or ion pumping.

Cytochemical demonstration of NPPase activity for detecting proton-translocating ATPase of Golgi complex in rat pancreatic acinar cells

An attempt at cytochemical demonstration of acidification proton-translocating ATPase (H(+)-ATPase) of Golgi complex in rat pancreatic acinar cells has been made by using p-nitrophenylphosphatase (NPPase) cytochemistry which is used for detecting of Na(+)-K(+)-ATPase (Mayahara et al. 1980) and gastric H(+)-K(+)-ATPase (Fujimoto et al. 1986). K(+)-independent NPPase activity was observed on the membrane of the trans cisternae of Golgi complex, but not inside of cisternae. The localization of NPPase activity is different from that of acid phosphatase activity where reaction products were seen on the inside of the trans Golgi cisternae. Since this activity was insensitive to vanadate, ouabain and independent of potassium ions, it was distinct from plasma membranous ATPases such as Na(+)-K(+)-ATPase and Ca2(+)-ATPase. The K(+)-independent NPPase activity was diminished by the inhibitors of H(+)-ATPase such as N-ethylmaleimide (NEM) and 4,4'-diisothiocyanostilbene-2,2'-disulfonic acid (DIDS). The NPPase reaction products were also seen on the membranes of other acidic organelles, i.e., lysosomes, endosomes, autophagosomes and coated vesicles. These results suggest that NPPase activity on the membrane of the Golgi complex and other acidic organelles corresponds with H(+)-ATPase which plays a role in acidification.