Isolation of ATPase I, the proton pump of chromaffin-granule membranes

Inhibition of the ecto-beta subunit of F1F0-ATPase inhibits proliferation and induces apoptosis in acute myeloid leukemia cell lines

BACKGROUND

Leukemia, a heterogeneous clonal disorder of hematopoietic progenitor cells, presents a world-wide health problem, especially in childhood. F1F0 ATPase, an inner mitochondrial enzyme, is expressed on the plasma membrane of tumor cells, and its inhibition induces both anti-angiogenic and anti-tumorigenic activity.

METHODS

Monoclonal Antibody (McAb) against ATPase was produced by polyethylene glycol-mediated fusions and screened by ELISA. Proliferation, cell cycle and apoptosis of cells were analyzed when the surface ATPase of cells was blockaded with McAb.

RESULTS

We detected cell-membrane expression of the F1F0 ATPase β subunit on 0.1% to 56% of the 11 cell lines derived from leukemia, including acute myeloid leukemia (AML). We produced a monoclonal antibody, McAb7E10, which recognizes both the native and recombinant ATPase β subunit, with a dissociation constant (KD) of 3.26E-10. We demonstrate that McAb7E10 binds to ATPase at the cell surface, where it is able to inhibit ATP synthesis. McAb7E10 significantly inhibited proliferation of AML cell lines in vitro: the relative inhibitory rates of 50 μg/mL McAb7E10 treated MV4-11and HL-60 cells were 69.6% and 81.9% respectively. Cell cycle analysis indicated that McAb7E10 significantly induced apoptosis in MV4-11 and HL-60 cells: the relative rates of apoptosis in 5, 10 and 50ug/mL McAb7E10 treated MV4-11 cells was 3.6 ± 0.83%, 8.4 ± 1.69% and 17.3 ± 2.56% compared to 1.5% ± 0.85% in mouse IgG treated cells (p < 0.01). The relative rate of apoptosis in 5, 10 and 50ug/mL McAb7E10 treated HL-60 cells was 5.5 ± 2.37%, 11.3 ± 3.62% and 19.9 ± 3.31% compared to 1.56% ± 0.97% in mouse IgG treated cells (p < 0.01). Annexin V staining demonstrated that the relative apoptotic rates in 50 μg/mL McAb7E10 treated MV4-11 and HL-60 cells were 50.5% ± 7.04% and 32.9% ± 4.52%, respectively, significantly higher than IgG control antibody treated cells were 21.9% ± 3.11% and 15.3% ± 3.95%, p < 0.01.

CONCLUSIONS

These findings indicate that ectopic expression of ATPase β subunit may be a tumor-associated antigen in hematological malignancies. The F1F0 ATPase β subunit provides a potential target for immunotherapy in AML and hematological malignancies.

Nonionic detergent phase extraction for the proteomic analysis of heart membrane proteins using label-free LC-MS

Heart diseases resulting in heart failure are among the leading causes of morbidity and mortality in the Western world and can result from either systemic disease (e.g., hypertensive heart disease, ischemic heart disease) or specific heart muscle disease (e.g., dilated cardiomyopathy/DCM). Subproteome analysis of such disease subsets affords a reduction in sample complexity, potentially revealing biomarkers of cardiac failure that would otherwise remain undiscovered in proteome wide studies. Label-free nanoscale LC-MS has been applied in this study to validate a Triton X-114-based phase enrichment method for cardiac membrane proteins. Annotation of the subcellular location combined with GRAVY score analysis indicates a clear separation between soluble and membrane-bound proteins with an enrichment of over 62% for this protein subset. LC-MS allowed confident identification and annotation of hydrophobic proteins in this control sample pilot study and demonstrates the power of the proposed technique to extract integral membrane-bound proteins. This approach should be applicable to a wider scale study of disease-associated changes in the cardiac membrane subproteome.

Impact of short- and medium-chain organic acids, acylcarnitines, and acyl-CoAs on mitochondrial energy metabolism

Accumulation of organic acids as well as their CoA and carnitine esters in tissues and body fluids is a common finding in organic acidurias, beta-oxidation defects, Reye syndrome, and Jamaican vomiting sickness. Pathomechanistic approaches for these disorders have been often focused on the effect of accumulating organic acids on mitochondrial energy metabolism, whereas little is known about the pathophysiologic role of short- and medium-chain acyl-CoAs and acylcarnitines. Therefore, we investigated the impact of short- and medium-chain organic acids, acylcarnitines, and acyl-CoAs on central components of mitochondrial energy metabolism, namely alpha-ketoglutarate dehydrogenase complex, pyruvate dehydrogenase complex, and single enzyme complexes I-V of respiratory chain. Although at varying degree, all acyl-CoAs had an inhibitory effect on pyruvate dehydrogenase complex and alpha-ketoglutarate dehydrogenase complex activity. Effect sizes were critically dependent on chain length and number of functional groups. Unexpectedly, octanoyl-CoA was shown to inhibit complex III. The inhibition was noncompetitive regarding reduced ubiquinone and uncompetitive regarding cytochrome c. In addition, octanoyl-CoA caused a blue shift in the gamma band of the absorption spectrum of reduced complex III. This effect may play a role in the pathogenesis of medium-chain and multiple acyl-CoA dehydrogenase deficiency, Reye syndrome, and Jamaican vomiting sickness which are inherited and acquired conditions of intracellular accumulation of octanoyl-CoA.

Ca(2+) and Na(+) dependence of 3-hydroxyglutarate-induced excitotoxicity in primary neuronal cultures from chick embryo telencephalons

Glutaryl-CoA dehydrogenase deficiency (also known as glutaric aciduria type I) is an autosomal, recessively inherited neurometabolic disorder with a distinct neuropathology characterized by acute encephalopathy during a vulnerable period of brain development. Neuronal damage in this disease was demonstrated to involve N-methyl-D-aspartate (NMDA) receptor-mediated neurotoxicity of the endogenously accumulating metabolite 3-hydroxyglutarate (3-OH-GA). However, it remained unclear whether NMDA receptors are directly or indirectly activated and whether 3-OH-GA disturbs the intracellular Ca(2+) homeostasis. Here we report that 3-OH-GA activated recombinant NMDA receptors (e.g. NR1/NR2A) but not recombinant alpha-amino-3-hydroxy-5-methyl-4-isoxazole propionate receptors (e.g. GluR-A/GluR-B) in HEK293 cells. Fluorescence microscopy using fura-2 as Ca(2+) indicator revealed that 3-OH-GA increased intracellular Ca(2+) concentrations in the presence of extracellular Ca(2+) in cultured chick neurons. Similar to glutamate-induced cell damage, 3-OH-GA neurotoxicity was modulated by extracellular Na(+). The large cation N-methyl-D-glucamine, which does not permeate NMDA receptor channels, enhanced 3-OH-GA-induced Ca(2+) increase and cell damage. In contrast, 3-OH-GA-induced neurotoxicity was reduced after replacement of Na(+) by Li(+), which permeates NMDA channels but does not affect the Na(+)/Ca(2+) exchanger in the plasma membrane. Spectrophotometric analysis of respiratory chain complexes I-V in submitochondrial particles from bovine heart revealed only a weak inhibition of 3-OH-GA on complex V at the highest concentration tested (10 mM). In conclusion, the present study revealed that NMDA receptor activation and subsequent disturbance of Ca(2+) homeostasis contribute to 3-OH-GA-induced cell damage.

3-Ureidopropionate contributes to the neuropathology of 3-ureidopropionase deficiency and severe propionic aciduria: a hypothesis

3-Ureidopropionate (3-UPA) is a physiologic metabolite in pyrimidine degradation. Pathological accumulation of 3-UPA in body fluids is found in 3-ureidopropionase deficiency and severe forms of propionic aciduria. Both diseases clinically present with a severe neuropathology involving gray and white matter as well as with a dystonic dyskinetic movement disorder. To date nothing is known about the toxic nature of this metabolite. The aim of the present study was to elucidate whether 3-UPA may act as endogenous neurotoxin. Exposure of cultured chick neurons to 3-UPA induced a concentration- and time-dependent neurodegeneration. Neuronal damage was reduced by the antioxidant alpha-tocopherol and the N-methyl-D-aspartate (NMDA) receptor antagonist MK-801. In contrast, the non-NMDA receptor antagonist CNQX, the metabotropic glutamate receptor antagonist L-AP3, and succinate showed no protective effect. Furthermore, 3-UPA elicited an increased production of reactive oxygen species followed by a delayed increase in intracellular calcium concentrations. Activity measurement of single respiratory chain complexes I-V revealed an inhibition of complex V activity, but not of the electron-transferring complexes I-IV by 3-UPA. In contrast, 3-UPA did not affect the mitochondrial beta-oxidation of fatty acids. In conclusion, our results provide strong evidence that 3-UPA acts as endogenous neurotoxin via inhibition of mitochondrial energy metabolism, resulting in the initiation of secondary, energy-dependent excitotoxic mechanisms.

Cytochrome b558 (p22phox) in the guinea-pig adrenal medulla

Paraganglionic cells are sensitive to hypoxia, and the involvement of a plasmalemmal cytochrome b558-like protein in oxygen sensing by these cells has been suggested, but neither the identity of the immunoreactive protein detected by immunohistochemistry nor its anticipated subcellular (i.e., plasmalemmal) localization were directly proven. Thus, we extended these studies to the largest paraganglion, i.e., the adrenal medulla, in the guinea-pig, which, due to its size and accessibility, allowed us to address both of these issues utilizing antisera raised against synthetic peptides of the small (22 kD) subunit of cytochrome b558, p22phox. Cytochrome b558 was originally identified in granulocytes and macrophages, and antisera against this phagocyte p22phox were utilized. Immunoreactivity to p22phox was observed in all adrenal medullary endocrine cells, and the identity of the immunoreactive protein to the small cytochrome b558-subunit was confirmed by Western blotting. Immuno-electron microscopy of ultrathin cryosections and of resin-embedded tissue demonstrated its subcellular localization in the dense core vesicles of endocrine A-cells but not in the plasma membrane. In conclusion, the present study documents the presence of the small subunit of cytochrome b558 in guinea-pig adrenal medullary cells, but its subcellular vesicular localization does not support the initial interpretation of cytochrome b558 serving as a plasmalemmal oxygen sensor.

Identification and characterization of a novel 9.2-kDa membrane sector-associated protein of vacuolar proton-ATPase from chromaffin granules

Vacuolar proton-translocating ATPase (holoATPase and free membrane sector) was isolated from bovine chromaffin granules by blue native polyacrylamide gel electrophoresis. A 5-fold excess of membrane sector over holoenzyme was determined in isolated chromaffin granule membranes. M9.2, a novel extremely hydrophobic 9.2-kDa protein comprising 80 amino acids, was detected in the membrane sector. It shows sequence and structural similarity to Vma21p, a yeast protein required for assembly of vacuolar ATPase. A second membrane sector-associated protein (M8-9) was identified and characterized by amino-terminal protein sequencing.

The vacuolar H+-ATPase: a universal proton pump of eukaryotes

The vacuolar H+-ATPase (V-ATPase) is a universal component of eukaryotic organisms. It is present in the membranes of many organelles, where its proton-pumping action creates the low intra-vacuolar pH found, for example, in lysosomes. In addition, there are a number of differentiated cell types that have V-ATPases on their surface that contribute to the physiological functions of these cells. The V-ATPase is a multi-subunit enzyme composed of a membrane sector and a cytosolic catalytic sector. It is related to the familiar FoF1 ATP synthase (F-ATPase), having the same basic architectural construction, and many of the subunits from the two display identity with one another. All the core subunits of the V-ATPase have now been identified and much is known about the assembly, regulation and pharmacology of the enzyme. Recent genetic analysis has shown the V-ATPase to be a vital component of higher eukaryotes. At least one of the subunits, i.e. subunit c (ductin), may have multifunctional roles in membrane transport, providing a possible pathway of communication between cells. The structure of the membrane sector is known in some detail, and it is possible to begin to suggest how proton pumping is coupled to ATP hydrolysis.

Analysis of nucleotide binding by a vacuolar proton-translocating adenosine triphosphatase

The vacuolar-type proton-translocatine adenosine triphosphatase from bovine adrenal secretory granules (chromaffin granules) was purified and reconstituted into proteoliposomes. The binding of nucleotides to the enzyme was studied by quantifying their effects on the rate of inactivation by N-ethylmaleimide (MalNEt) of ATP-dependent proton translocation, and by direct measurement of the binding of [3H]MgADP. The results of these experiments are consistent with a model of the enzyme that had been developed as a result of kinetic experiments, the features of which are that the enzyme exists in two states, each containing three nucleotide-binding sites on catalytic subunits, and that nucleoside diphosphates regulate the enzyme by binding with high affinity to a single site in the inactive T state of the enzyme. Under the conditions of the experiments, MalNEt inactivated the ATPase in a pseudo-first order reaction. Rate constants of inactivation were reduced in the presence of MgADP, MgIDP and free ADP; the kinetics of protection suggested that the two conformational states of the enzyme were inactivated at different rates and also confirmed the existence of two different types of binding site for MgADP. Low nucleotide concentrations afforded partial protection from MalNEt; this was ascribed to binding of nucleotide to the regulatory site causing a shift in the conformational equilibrium towards the T state, which was more slowly inactivated than the unliganded R state of the enzyme. At higher nucleotide concentrations, binding at the catalytic site afforded complete protection from MalNEt. Protection by MgADP[S] and magnesium 2'- and 3'-O-[4-benzoylbenzoyl]adenosine 5'-triphosphate showed simpler kinetics but was also consistent with previously reported kinetic results. Analysis of subunit labelling with [3H]MalNEt showed that the three 72-kDa (catalytic) subunits were alkylated by MalNEt with similar rate constants, consistent with a symmetrical arrangement of the catalytic subunits, in contrast to the situation in F-type ATPases. Analysis of the binding of [3H]MgADP also confirmed the results of kinetic experiments. MgADP was shown to bind to the enzyme with an apparent dissociation constant of about 66 nM; assuming that the nucleotide binds only to the T-state, the true dissociation constant is < 1 nM. Using Blue Native polyacrylamide gel electrophoresis to separate the holo-ATPase from the membrane sector, the stoichiometry of binding was calculated to be 0.6 mol/mol enzyme, confirming the existence of a single regulatory site for MgADP. However, binding of MgADP to the enzyme was much slower than could be accounted for by the measured dissociation constants, suggesting that it is rate limited by a step such as a protein conformational change. Treatment designed to remove endogenous nucleotide had no effect on the rate or extent of binding of MgADP.

Evidence for a K+ channel in bovine chromaffin granule membranes: single-channel properties and possible bioenergetic significance

A K+ channel was incorporated into voltage-clamped planar lipid bilayers from bovine chromaffin granules and resealed granule membranes ("ghosts"). It was not incorporated from plasma membrane-rich fractions from the adrenal medulla. The channel had a conductance of approximately 400 pS in symmetric 450 mM KCl, with the permeability sequence K+ > Rb+ > Cs+ > Na+ > Li+, and was insensitive to both Ca2+ and charybdotoxin. It exhibited complex gating kinetics, consistent with the presence of multiple open and closed states, and its gating was voltage-dependent. The channels appeared to incorporate into bilayers with the same orientation, and were blocked from one side (the side of vesicle addition) by 0.2-1 mM TEA+. The block was slightly voltage-dependent. Acidification of resealed granule membranes in response to external ATP (which activated the vacuolar-type ATPase) was significantly reduced in the presence of 1 mM intralumenal TEACl (with 9 mM KCl), and parallel measurements with the potential-sensitive dye Oxonol V showed that such vesicles tended to develop higher internal-positive membrane potentials than control vesicles containing only 10 mM KCl. 1 mM TEA+ had no effect on proton-pumping activity when applied externally, and did not directly affect either the proton-pumping or ATP hydrolytic activity of the partially-purified ATPase. These results suggest that chromaffin granule membranes contain a TEA(+)-sensitive K+ channel which may have a role in regulating the vesicle membrane potential.

The adrenal chromaffin granule: a model for large dense core vesicles of endocrine and nervous tissue

More than 25 years have elapsed since R. E. Coupland made his classic observations on the ultrastructure of chromaffin granules, on the histochemical differentiation of noradrenaline and adrenaline storage granules and on their release by exocytosis. This essay attempts to demonstrate that subsequent studies on the biochemistry of chromaffin granules have yielded analytical and functional data relevant for all large dense core vesicles of endocrine and nervous tissue.

Thermoreactive water-soluble polymers, nonionic surfactants, and hydrogels as reagents in biotechnology

Thermoprecipitating polymers such as poly (N-isopropylacrylamide), poly(N-vinyl caprolactam), and some ethylene oxide-containing surfactants appear to be suitable for developing new separation systems to complement traditional precipitation, chromatography, and extraction of biological molecules. The nature of thermally induced phase separation of polymers and nonionic surfactants is discussed and examples are given. Covalent coupling of an enzyme to a thermoprecipitable polymer results in a biocatalyst which combines the qualities of soluble and immobilized enzymes. Biocatalysts of this type can be separated from reaction media by precipitation after temperature increase. The use of thermoprecipitating polymer-protein conjugates in immunoassays overcomes one of the shortcomings of traditional methods with solid sorbent-linked antigen or antibody-diffusional limitations. Thermoreactive hydrogels produced by crosslinking of thermoprecipitating polymers can be successfully used for concentrating macromolecules or microbe-rich slurries. Alternate volume changes of hydrogels on heating and cooling produce a "hydraulic pump" which can enhance the productivity of an immobilized biocatalyst. Hydrogels could be used to control reaction or diffusion rates by a thermal feedback mechanism.

H(+)-ATPase and transport of DOPAC, HVA, and 5-HIAA in monoamine neurons

The effects of N-methylmaleimide (N-MtM), a vacuolar H(+)-ATPase inhibitor, were evaluated in the putamen of the cat to study the in vivo transport mechanisms of dopamine (DA), 5-hydroxytryptamine (5-HT), and their metabolites 3,4-dihydroxyphenylacetic acid (DOPAC), homovanillic acid (HVA), and 5-hydroxyindolacetic acid (5-HIAA), using the brain focal microdialysis technique combined with HPLC. The addition of N-MtM to the perfusate altered invariably the flux of the DOPAC, HVA, and 5-HIAA in a similar pattern, resulting in a decrease of the extracellular levels of such metabolites, its extent being N-MtM concentration dependent, thus indicating that the mechanism(s) of such a decrease is (are) related most likely to decreased transport from the intracellular to the extracellular space as the consequence of the inhibition of the vacuolar H(+)-ATPase of DA and 5-HT neurons by the N-MtM. Furthermore, N-MtM masked the release of DA and 5-HT produced by KCl 120 mmol/l. Indeed, N-MtM increased the extracellular levels of such transmitters to values exceeding 4 to 6 times of those produced by KCl 120 mmol/l alone, which suggests that vacuolar H(+)-ATPase is probably involved also in the retention and/or reuptake process of DA and 5-HT.

Characterization of an ATP-driven H+ pump in human placental brush-border membrane vesicles

The presence of an ATP-driven H+ pump as measured by H+ uptake upon addition of ATP was not demonstrable in human placental brush-border membrane vesicles when used in their native form, owing to their right-side-out orientation. However, the presence of the H+ pump in these membranes became evident when the membrane vesicles were transiently exposed to 1% cholate, with subsequent removal of the detergent to re-form the vesicles. Apparently, cholate pretreatment reoriented the H+ pump from an inward-facing configuration to outward-facing. Consequently, H+ uptake in response to externally added ATP was easily demonstrable in these cholate-pretreated vesicles by using the delta pH indicator Acridine Orange. In addition, bafilomycin A1-sensitive ATPase activity was measurable in cholate-pretreated vesicles, but not in native intact vesicles, indicating reorientation of the H+ pump. The reoriented H+ pump was electrogenic because H+ uptake was stimulated by an inside-negative anion-diffusion potential or when the vesicles were voltage-clamped. ATP supported H+ uptake with an apparent Km of 260 microM. ITP and GTP supported the pump activity partially, whereas CTP and UTP did not. Mg2+ and Mn2+ were the most preferred bivalent cations. Co2+ and Zn2+ showed partial activity, whereas Ca2+ and Ba2+ showed little or no activity. The pump was inhibited by nanomolar concentrations of bafilomycin A1 and micromolar concentrations of N-ethylmaleimide, p-chloromercuribenzenesulphonate, NN-dicyclohexylcarbodi-imide and 7-chloro-4-nitrobenzo-2-oxa-1,3-diazole, but was relatively insensitive to oligomycin, vanadate and NaN3. The inhibition by N-ethylmaleimide was protectable by ATP. It is concluded that human placental brush-border membranes possess an ATP-driven H+ pump and that, on the basis of its characteristics, it belongs to the class of vacuolar (V-type) H+ pumps.

Evidence for an ATP-driven H(+)-pump in the plasma membrane of the bovine corneal epithelium

In a highly enriched plasma membrane fraction isolated from the bovine corneal epithelium, MgATP dependent intravesicular acidification was identified by measuring Acridine Orange quenching. The rate of acidification was increased 2.7-fold by pre-exposure of the membranes to 1% cholate which was subsequently removed by Sephadex G-50 column chromatography. However, in a lysosomal fraction whose enrichment with respect to the homogenate was 82-fold in N-acetyl-beta-D-glucosaminidase, cholate pre-exposure had no significant effect on the rate of intralysosomal acidification. This difference is assumed to reflect reorientation by cholate of the H(+)-pump's normally inaccessible ATP-binding site in right-side-out vesicles of the plasma membrane-enriched fraction to a configuration in which this site becomes accessible to externally added ATP. In contrast, the ATP-binding site of the H(+)-pump in the lysosomal fraction is completely exposed to the exterior even in the absence of cholate treatment. The characteristics of the H(+)-pump in the plasma membrane fraction was subsequently determined using cholate-pretreated membrane vesicles. The rank order of nucleotide support of the H(+)-pump activity was: ATP >> GTP > ITP. However, UTP and CTP were totally inactive. The pump is electrogenic because the activity of the pump was enhanced in voltage-clamped membrane vesicles. Substitution of Mg2+ with Mn2+ did not change the acidification rate but Co2+ only partly activated whereas Ca2+ and Zn2+ were ineffective as activators. The H(+)-pump was relatively unaffected by oligomycin, azide or vanadate but completely inhibited by 10 microM NEM or NBD-Cl and 92% inhibited by 20 microM DCCD.(ABSTRACT TRUNCATED AT 250 WORDS)

Purification and characterization of a putative proenkephalin cleaving enzyme

A putative proenkephalin-cleaving enzyme (PCE) extracted from bovine adrenal chromaffin granules was purified with soybean trypsin inhibitor high-performance affinity chromatography. The 12,600-fold purified enzyme was maximally active at pH 8.0. The enzyme was completely inhibited with lima bean trypsin inhibitor (0.1 mg/ml), soybean trypsin inhibitor (0.1 mg/ml), and p-(chloromercuri)benzenesulfonic acid (1.0 mM), indicating PCE is a serine protease with cysteine residues likely to be involved in its structure or activity. It exhibited significant autoproteolysis without specific substrates present. The substrate specificity and kinetic constants with the enkephalin-containing (EC) peptides Leu-9 and proenkephalin Peptides B, E, and F as substrates were studied. The cleavage patterns were substantially different than with trypsin digestion. PCE specifically recognized the paired basic amino acid residues and predominantly cleaved the peptide bonds between Lys and Arg sites and peptide bonds after Lys-Lys and Arg-Arg sites. Different Km and Vmax values for the different Lys-Arg sites indicate sequences in addition to the paired basic residues can affect enzyme activity. Also, the lower Km and Vmax of Peptide E suggest a higher affinity for this peptide but much slower cleavage. The C-terminally located Lys-Arg site appears responsible for this high affinity. Based on these observations, we propose the following: (a) the primary structure of these peptides contains enough information to be processed correctly by PCE and (b) PCE may be regulated by pH and Peptide E to prevent extensive processing of the intermediate EC peptides which are the major opioid peptides found in the adrenal chromaffin granules.

Rapid purification and reconstitution of a plant vacuolar ATPase using Triton X-114 fractionation: subunit composition and substrate kinetics of the H(+)-ATPase from the tonoplast of Kalanchoë daigremontiana

A rapid procedure for the purification and reconstitution into proteoliposomes of the H(+)-translocating ATPase of plant vacuolar membranes is reported. It involves fractionation of the tonoplast with Triton X-114, resolubilization of the ATPase with octyl glucoside in the presence of a mixture of phosphatidylcholine, phosphatidylserine and cholesterol (27:53:20, by weight), and removal of the detergent by gel-filtration. Starting with partially purified vacuolar membranes, the procedure can be accomplished in about 2 hours. It has been applied to the H(+)-ATPase from the crassulacean plant Kalanchoë daigremontiana, from which it yields vesicles with a specific ATPase activity of about 3 mumol/min per mg protein. The purified enzyme contains polypeptides of apparent molecular mass 72, 57, 48, 42, 39, 33 and 16 kDa; these polypeptides also co-sediment on centrifugation of the solubilized ATPase through glycerol gradients. The 16-kDa subunit is labelled with [14C]dicyclohexylcarbodiimide. There is no evidence for a larger ATPase subunit in this preparation. The reconstituted ATPase proteoliposomes undergo ATP-dependent acidification, which can be measured by quenching of the fluorescence of 9-aminoacridine. The initial rate of fluorescence quenching is a measure of the rate of H+ translocation, and is directly proportional to the vesicle protein concentration, so the preparation is suitable for studying the kinetics of the tonoplast H(+)-ATPase. The dependence of the rate of fluorescence quenching on the concentration of MgATP is well fitted by the Michaelis equation, with a Km value about 30 microM. ATP can be replaced by dATP, ITP, GTP, UTP or CTP, and Mg2+ by Mn2+ or Ca2+; kinetic parameters for these substrates are reported. In contrast, hydrolysis of MgATP shows complex kinetics, suggestive either of negative cooperativity between nucleotide-binding sites, or of two non-interacting catalytic sites. Both the hydrolytic and the H(+)-translocating activities of the proteoliposomes are inhibited by nitrate, though not in parallel, the latter activity being the more sensitive. Both activities are inhibited in parallel by bafilomycin A1, which does not produce complete inhibition; the bafilomycin-insensitive component has complex ATPase kinetics similar to those of the uninhibited enzyme.

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.

Head and stalk structures of soybean vacuolar membranes

Highly purified tonoplast fractions isolated by preparative free-flow electrophoresis from hypocotyls of etiolated soybean (Glycine max L. (Merr.)) were examined by negative-staining electron microscopy, and many but not all vesicles were found to exhibit head and stalk structures resembling the 9-nm stalked F1 ATPase particles reported previously for Neurospora (Bowman et al., 1989, J. Biol. Chem. 264, 15606-15612). The structures show distinguishing characteristics similar to those for Neurospora. These include a cleft in the particle not exhibited by mitochondrial F1 ATPase and a tendency to disappear from the membrane when treated with nitrate plus Mg(-2+)-ATP-containing solutions. The position of the stalked ATPase structures, indicates that some of the tonoplast vesicles were oriented cytoplasmic side out whereas others were oriented cytoplasmic side in.

Chilling-Induced Inactivation and Its Recovery of Tonoplast H-ATPase in Mung Bean Cell Suspension Cultures

The processes involved in adaptation to cold temperature were examined by growing suspension cultured cells of mung bean (Vigna radiata [L.] Wilczek) at 2 degrees C for various periods of time and assaying the activities of various membrane-bound enzymes in vitro. The tonoplast H(+)-ATPase activity and the ATP-proton transport extracted from cells incubated at 2 degrees C declined rapidly and reached a minimum level after 10 hours. The inactivation was reversible within 24 hours of chilling. The recovery of the cold-inactivated H(+)-ATPase was found to proceed in two steps, a faster recovery of ATP hydrolysis activity and a slower recovery of the proton transport. The recovery was markedly inhibited by the presence of azide, but not affected by 0.578 millimolar cycloheximide. This suggested the involvement of an energy process that had no requirement for de novo synthesis of protein. The cold-induced inactivation of the H(+)-ATPase may be due to a structural alteration of the enzyme. The slower recovery of proton transport relative to ATP hydrolysis during warming suggests that the protogenic domains in the enzyme may be affected differently by chilling.

Partial purification and characterization of the vacuolar H(+)-ATPase of mammalian synaptic vesicles

Several major proteins of synaptic vesicles from rat or cow brain sediment as a large complex on sucrose density gradients when solubilized in nonionic detergents. A vacuolar H(+)-ATPase identified by sensitivity to bafilomycin A1 appears to be associated with this oligomeric protein complex. Two subunits of this complex, synaptic vesicle proteins S and U, correspond to the 57-kDa (B) and 39-kDa accessory (Ac39) subunits, respectively, of bovine chromaffin granule vacuolar H(+)-ATPase as shown by Western immunoblot analysis. The five subunits of the oligomeric complex constitute approximately 20% of the total protein of rat brain synaptic vesicles. Taken together, these results strongly suggest that the abundant, multisubunit complex partially purified from brain synaptic vesicles by density gradient centrifugation is a vacuolar H(+)-ATPase. Bafilomycin A1 completely blocks proton pumping in rat brain synaptic vesicles as measured by [14C]methylamine uptake and also blocks catecholamine accumulation measured by [3H]dopamine uptake. Moreover, ATPase activity, [14C]methylamine uptake, and [3H]dopamine uptake are inhibited by bafilomycin A1 at similar I50 values of approximately 1.7 nmol/mg of protein. These findings indicate that the vacuolar H(+)-ATPase is essential for proton pumping as well as catecholamine uptake by mammalian synaptic vesicles.

A two-dimensional electrophoretic analysis of the proteins and glycoproteins of liver plasma membrane domains and endosomes. Implications for endocytosis and transcytosis

1. Polypeptides of liver plasma membrane fractions enriched in three surface domains of hepatocytes, blood-sinusoidal, lateral and bile canalicular, were analysed by isoelectric focusing (IEF) and non-equilibrium pH gel electrophoresis (NEPHGE) across a wide pH range, followed by SDS/PAGE. The overall Coomassie Blue-stained polypeptide patterns in the fractions were different. lateral plasma membrane fractions contained a characteristically higher number of polypeptides focusing at the basic pH range, whereas few basic polypeptides were present in sinusoidal plasma membrane fractions. The glycoproteins in these plasma membrane fractions stained by a lectin overlay technique with radio-iodinated concanavalin A, wheat-germ agglutinin and a slug lectin, were also different. 2. The polypeptides and glycoproteins of 'early' and 'late' endosome fractions were also compared by two-dimensional electrophoresis. Their composition was shown by Coomassie Blue staining, lectin overlay staining and in membranes metabolically labelled with [35S]methionine to be generally similar. The glycoproteins of sinusoidal plasma membranes and early and late endosomes were generally similar, but major differences in polypeptides of molecular mass 20-50 kDa, pI 7.5-8.5, in plasma membranes and endosomes were demonstrated, with a specific population of basic (pI 8-9) low-molecular-mass polypeptides being present at highest levels in 'late' endosomal fractions (shown by Coomassie Blue staining). 3. Analysis of the distribution of three specific membrane glycoproteins identified by using immunoblotting techniques showed that the asialoglycoprotein and the divalent-cation-sensitive mannose 6-phosphate receptors were present in sinusoidal plasma membrane and in early and late endocytic fractions: they were not detected in canalicular plasma membrane fractions. In contrast, 5'-nucleotidase was detected in all fractions examined. The role of the endocytic compartment in regulating trafficking pathways between the plasma membrane domains of the hepatocyte is discussed.

Vacuolar H(+)-ATPase of adrenal secretory granules. Rapid partial purification and reconstitution into proteoliposomes

A procedure has been developed for the rapid purification and reconstitution into phospholipid vesicles of the proton-translocating ATPase of bovine adrenal chromaffin-granule membranes. It involves fractionation of the membranes with Triton X-114, resolubilization of the ATPase with n-octyl glucoside, addition of purified lipids and removal of detergent by gel filtration. The entire process can be completed within 2 h. H+ translocation was detected by the ATP-dependent quenching of the fluorescence of a permeant weak base. The effect of varying the lipid composition of the vesicles on ATP hydrolysis and H+ translocation by the reconstituted enzyme was examined. ATPase activity was maximally increased about 4-fold by added lipid, but was relatively insensitive to its composition, whereas vesicle acidification was absolutely dependent on the addition of phospholipids and cholesterol.

Purification and kinetic properties of a membrane-bound phosphatidylinositol kinase of the bovine adrenal medulla

Phosphatidylinositol (PI) kinase (EC 2.7.1.67), an integral membrane protein of chromaffin granule ghosts of the bovine adrenal medulla, was found to phosphorylate PI in the 4-position of the inositol ring. The PI kinase was purified about 200-fold from a membrane fraction containing chromaffin granules and microsomes by extraction with Triton X-114, followed by phase partition (clouding) and heparin Sepharose chromatography. The PI kinase preparation (specific activity of 5.1 nmol PIP/mg protein per min) was free from other enzymatic activities that metabolize polyphosphoinositides. Km values of 55 microM and 40 microM for ATP and PI, respectively, were estimated for the purified enzyme. Concentrations of Triton X-100 above the critical micellar concentration (0.01%, w/v) were necessary to support significant enzyme activity, which was optimal at about 0.1% (w/v). Its dependence of pH was similar to that of the membrane-bound enzyme, with a broad optimum around pH 7. Mes in the millimolar concentration range was found to strongly inhibit the activity of the purified PI kinase (I50 at about 4 mM). The enzyme was almost totally inhibited by low micromolar concentrations of free calcium, and stimulated by hydrophilic cations, e.g., Mg2+ and poly(L-lysine), with the same potencies as for the membrane-bound enzyme. The amphiphilic cation trifluoperazine, however, stimulated the activity of purified PI kinase less effectively than the membrane-bound enzyme (Husebye, E.S. and Flatmark, T. (1988) Biochem. Pharmacol. 37, 449-456), whereas the inhibitory effect of near millimolar concentrations of trifluoperazine was the same for the two forms of the enzyme. It is concluded that the membrane-bound PI kinase of this tissue is of type II according to the classification of Cantley and co-workers (Whitman et al. (1987) Biochem. J. 247, 165-174).

Subunit composition of vacuolar membrane H(+)-ATPase from mung bean

The vacuolar H(+)-ATPase from mung bean hypocotyls was solubilized from the membrane with lysophosphatidycholine and purified by QAE-Toyopearl column chromatography. The purified ATPase was active only in the presence of exogenous phospholipid and was inhibited by nitrate, dicyclohexyl carbodiimide and Triton X-100, but not by vanadate or azide. Dodecyl sulfate/polyacrylamide gel electrophoresis of the purified ATPase yielded ten polypeptides of molecular masses of 68 kDa, 57 kDa, 44 kDa, 43 kDa, 38 kDa, 37 kDa 32 kDa, 16 kDa, 13 kDa and 12 kDa. All polypeptides remained in the peak activity fraction after glycerol density gradient centrifugation. Nine of them, excluding the 43-kDa polypeptide, comigrated in a polyacrylamide gradient gel in the presence of 0.1% Triton X-100. The 16-kDa polypeptide could be labeled with [14C]dicyclohexylcarbodiimide. The amino-terminal amino acid sequence of the isolated 68-kDa polypeptide generally agreed with that deduced from the cDNA for the carrot 69-kDa subunit [Zimniak, L., Dittrich, P., Gogarten, J. P., Kibak, H. & Taiz, L. (1988) J. Biol. Chem. 263, 9102-9112]. Thus, mung bean vacuolar H(+)-ATPase seems to consist of nine distinct subunits.

Purification and subunit composition of a cholinergic synaptic vesicle glycoprotein, phosphointermediate-forming ATPase

A glycoprotein ATPase in cholinergic synaptic vesicles of Torpedo electric organ was solubilized with octa-ethylene glycol dodecyl ether detergent. Study of potential stabilizing factors identified crude brain phosphatidylserine, glycerol, dithiothreitol, and protease inhibitors as of value in maintaining activity. The ATPase was purified from the solubilized, stabilized material by glycerol density gradient band sedimentation velocity ultracentrifugation, and hydroxylapatite, wheat germ lectin affinity, and size exclusion chromatographies. The pure ATPase had a specific activity of about 37 mumol ATP hydrolyzed/min/mg protein. After sodium dodecyl sulfate-polyacrylamide gel electrophoresis, the purified material typically exhibited three polypeptides of molecular masses 110, 104, and 98 kilodaltons (kDa) and a fourth diffuse polypeptide of 60 kDa. This composition suggests that the ATPase is a member of the P-type, or phosphointermediate-forming, family, but it was shown to be distinct from the ouabain-sensitive Na+,K+- and CA2+-stimulated Mg2+-ATPases. The purified vesicle enzyme was rapidly phosphorylated by [gamma-32P]ATP on about 14% of the subunits with molecular weights of 98,000-110,000. About 16% of the ATPase was phosphorylated in whole-vesicle ghosts in a manner consistent with formation of a phosphointermediate, thus confirming the P-type nature of this enzyme.

Topography of a vacuolar-type H+-translocating ATPase: chromaffin-granule membrane ATPase I

Proteins exposed on the cytoplasmic face of isolated chromaffin granules were labelled by lactoperoxidase-catalysed radioiodination and by non-enzymic biotinylation. Granule membranes were then prepared, and the H+-translocating ATPase isolated by fractionation with Triton X-114. The labelling of individual ATPase subunits was assessed by polyacrylamide-gel electrophoresis, followed by autoradiography or by blotting and decoration with 125I-labelled streptavidin. Subunits of 72, 57 and kDa were strongly labelled, and could be removed from the membrane at pH 11: they are therefore extrinsic proteins. The 120 kDa subunit was also labelled, but it was not solubilized at pH 11. Photolabelling with a hydrophobic probe indicated that this subunit penetrates the bilayer, and enzymic degradation studies showed the presence of N-linked oligosaccharides; this subunit therefore spans the chromaffin-granule membrane. Labelling of the 17 kDa subunit occurred predominantly on the extracytoplasmic (matrix) face of the granule membrane. These results are consistent with this V-type ATPase having a structure that is generally similar to that of mitochondrial (F-type) ATPases, although the attachment of the 120 kDa subunit may be asymmetrical.

Human endomembrane H+ pump strongly resembles the ATP-synthetase of Archaebacteria

Preparations of mammalian H+ pumps that acidify intracellular vesicles contain eight or nine polypeptides, ranging in size from 116 to 17 kDa. Biochemical analysis indicates that the 70- and 58-kDa polypeptides are subunits critical for ATP hydrolysis. The amino acid sequences of the major catalytic subunits (58 and 70 kDa) of the endomembrane H+ pump are unknown from animal cells. We report here the complete sequence of the 58-kDa subunit derived from a human kidney cDNA clone and partial sequences of the 70- and 58-kDa subunits purified from clathrin-coated vesicles of bovine brain. The amino acid sequences of both proteins strongly resemble the sequences of the corresponding subunits of the vacuolar H+ pumps of Archaebacteria, plants, and fungi. The archaebacterial enzyme is believed to use a H+ gradient to synthesize ATP. Thus, a common ancestral protein has given rise to a H+ pump that synthesizes ATP in one organism and hydrolyzes it in another and is highly conserved from prokaryotes to humans. The same pump appears to mediate the acidification of intracellular organelles, including coated vesicles, lysosomes, and secretory granules, as well as extracellular fluids such as urine.

ATP-dependent H+ transport by the turtle bladder: NBD-C1 preferentially inhibits the vanadate-insensitive component in isolated membranes

We investigated the inhibitory effects of 7-chloro-4-nitrobenzo-2-oxa-1,3-diazole (NBD-Cl) on ATP-dependent H+ accumulation by membrane vesicles prepared from the turtle urinary bladder epithelium. NBD-Cl at 30 microM was found to completely inhibit the vanadate-insensitive component of H+ transport, with half-maximal inhibition occurring at 4.2 to 5.4 microM. In contrast, the vanadate-inhibitable component was unaffected by 30 microM NBD-Cl. At high concentrations (300 microM), both components were fully inhibited. The results confirm the presence of two distinct H+ transport processes in turtle bladder membranes and identify selective inhibitors, NBD-Cl and vanadate, for each process.

A sodium/proton antiporter in chromaffin-granule membranes

Chromaffin granules, the secretory vesicles of the adrenal medulla, have a Na+/H+ exchange activity in their membranes which brings their proton gradient into equilibrium with a Na+ gradient. This explains why Na+ is mildly inhibitory to amine transport (which is driven by the H+ gradient) The activity can be demonstrated by using accumulation of 22Na+ in response to a pH gradient that is either imposed by diluting membrane 'ghosts' into alkaline media, or generated by ATP hydrolysis. It can also be monitored indirectly by fluorescence measurements in which the pH inside 'ghost' is monitored by quenching of a fluorescent weak base. This method has been used to monitor Na+ entry into acid-loaded 'ghosts' of H+ entry into methylamine accumulation. The exchanger appears to be reversible and non-electrogenic, with a stoichiometry of 1:1. Using an indirect assay we measured an apparent Km for Na+ of 4.7 mM, and a Ki for amiloride, a competitive inhibitor, of 0.26 mM. Direct assays using 22Na+ suggested a higher Km. Ethylisopropylamiloride was not inhibitory.

An immunoreactive 8-azido ATP-labeled protein common to the lysosomal and chromaffin granule membrane

The H+-ATPases of eukaryotic cell organelles, including the rat liver lysosomal (tritosomal) H+-ATPase and the bovine chromaffin granule ATPase, exhibit similarities in function, substrate requirements, and inhibitor responses. We have explored the possibility that these pumps also exhibit immunological similarities, and that common determinants may be present on polypeptides important to function, such as ATP binding. Toward this end, antibodies were produced in rabbits against a highly purified, detergent-solubilized and fractionated chromaffin granule proton pump preparation. This antibody reacted with a 70-80 kDa protein of the lysosomal membrane on Western blots. We have previously shown that photolysis with 8-azido-ATP inhibits lysosomal N-ethylmaleimide-sensitive, vanadate-, ouabain- and oligomycin-insensitive ATP hydrolysis and H+ transport, with concomitant labeling of a 70-80 kDa membrane protein, amongst others. Here, we report that the photolysis with 8-azido-ATP also leads to inhibition of chromaffin granule H+ pump function and pump-related ATP hydrolysis, with concomitant N-ethylmaleimide-sensitive, ATP-protectable, 8-azido-[alpha-32P]ATP labeling. The anti-chromaffin granule antibody reacts with an approx. 70 kDa protein of the chromaffin granule and the lysosome. This raises the possibility that the 70 kDa 8-azido-ATP-reactive, immunologically similar proteins may play a similar role in pump function such as ATP binding and/or hydrolysis in these organelles.

Purification and reconstitution of the proton-translocating ATPase of Golgi-enriched membranes

Kidney cortex microsomes enriched in Golgi markers and probably also containing endosomes were isolated by cell fractionation and found to contain a proton-translocating ATPase that was inhibited by N-ethylmaleimide (NEM). This NEM-sensitive ATPase was solubilized with n-octyl glucoside and purified using anion-exchange sievorptive chromatography on sequential DEAE-Sephadex and QAE-Sephadex columns followed by a final hydroxyapatite HPLC column. The purified enzyme, with a specific activity of 4.4 mumol.mg-1.min-1 was completely inhibited by NEM. Addition of asolectin and removal of the detergent by dialysis resulted in reconstitution of NEM-sensitive electrogenic proton transport. This vacuolar ATPase is composed of five polypeptides with apparent molecular masses of 68, 58, 40, 37, and 16 kDa.

Bafilomycins: a class of inhibitors of membrane ATPases from microorganisms, animal cells, and plant cells

Various membrane ATPases have been tested for their sensitivity to bafilomycin A1, a macrolide antibiotic. F1F0 ATPases from bacteria and mitochondria are not affected by this antibiotic. In contrast, E1E2 ATPases--e.g., the K+-dependent (Kdp) ATPase from Escherichia coli, the Na+,K+-ATPase from ox brain, and the Ca2+-ATPase from sarcoplasmic reticulum--are moderately sensitive to this inhibitor. Finally, membrane ATPases from Neurospora vacuoles, chromaffin granules, and plant vacuoles are extremely sensitive. From this we conclude that bafilomycin A1 is a valuable tool for distinguishing among the three different types of ATPases and represents the first relatively specific potent inhibitor of vacuolar ATPases.