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PubMed1983

RBC membrane adenosine triphosphatase activities in patients with major affective disorders.

Red blood cell Na+, K+-, Mg2+-, and Ca2+-adenosine triphosphatase (ATPase) activities were studied longitudinally in eight patients with affective disorders and 12 healthy volunteers. The patients had a higher mean Ca2+-ATPase activity than the volunteers, and the fluctuations in all three ATPase activities were greater in the patients than in the volunteers. Even though the mean Ca2+-ATPase activity was higher during manias and euthymic periods than during depressions, mood and ATPase activities did not correlate with each other in all patients. Lithium carbonate treatment did not alter the ATPase activities, and the quantity of vanadium present in the membranes could not account for the variations in the enzyme activities observed. We suggest that either the RBCs of manic-depressive patients are very sensitive to fluctuations of a lipophilic ATPase activity--regulating factor present in plasma or the patients have at times high levels of such a factor. In some patients, the level of this hypothesized regulator may fluctuate in synchrony with mood changes.

Adenosine Triphosphatases↗
PubMed1982

The mitochondrial adenosine triphosphatase of Acanthamoeba castellanii. Partial characterization and changes in activity during exponential growth.

1. The mitochondrial adenosine triphosphatase (ATPase) of Acanthamoeba castellanii is Mg2+-requiring (optimum cation: ATP ratio of 1.5) and has two pH optima of activity (at pH 6.6 and 8.1). 2. ATPase activity of submitochondrial particles is effectively inhibited by twelve different inhibitors of energy conservation suggesting similarities in inhibitor-binding sites to other previously characterized complexes. 3. Gel filtration by passage through Sephadex G-50 increases ATPase activity of submitochondrial particles between 1.5 and 3.5 fold indicating the presence of a low molecular weight inhibitor protein. 4. After removal of the inhibitor protein, sensitivity to inhibitors of energy conservation decreases by between 1.5 and 14 fold. Crude F1-inhibitor preparations from A. castellanii, Schizosaccharomyces pombe, Tetrahymena pyriformis and bovine heart also inhibit ATPase activity. 5. Large variations in ATPase activity, F1-inhibitor protein activity, and amounts of immunologically-determined ATPase protein were observed during exponential growth, and the correlation between changes in these measurements is discussed. 6. The results are also discussed highlighting the similarities between the mitochondrial ATPase of A. castellanii and other mitochondrial ATPases.

Adenosine Triphosphatases↗
PubMed1989

Possible mechanism for the inhibition of gastric (H+ + K+)-adenosine triphosphatase by the proton pump inhibitor AG-1749.

Mechanisms related to the inhibition of (H+ + K+)-adenosine triphosphatase (ATPase) by 2-[[[3-methyl-4-(2,2,2-trifluoroethoxy)-2-pyridyl]methyl] sulfinyl]-1H-benzimidazole (AG-1749) were studied using canine gastric microsomes. AG-1749 (1-100 microM) inhibited the K+-stimulated ATP hydrolysis and vesicular accumulation of H+. AG-1749 bound to the microsomes concentration-dependently and decreased the number of free SH groups; the binding correlating with the enzyme inhibition. Both the binding and inhibition were antagonized by dithiothreitol. N-ethylmaleimide inhibited the (H+ + K+)-ATPase and decreased the binding of [14C]AG-1749 to the microsomes. The inhibitory effect of AG-1749 gradually increased with incubation time, and was enhanced by lowering the pH. AG-2000 and AG-1812, acid-induced rearrangement products of AG-1749, inhibited (H+ + K+)-ATPase potently, rapidly and independently of pH; the inhibition was antagonized by dithiothreitol. We propose that AG-1749 is transformed into its active forms within the acidic compartment of the parietal cells and that the active compounds inhibit (H+ + K+)-ATPase activity by reacting with the SH groups of the enzyme.

2-Pyridinylmethylsulfinylbenzimidazoles↗
PubMed1976

The susceptibility of the glycoprotein from the purified (Na+, K+)-activated adenosine triphosphatase to tryptic and chymotryptic degradation with and without Na+ and K+.

Purified (Na+, K+)-activated adenosine triphosphatase ((Na+, K+)-ATPase, ATP phosphohydrolase, EC 3.6.1.3) has been subjected to trypsin and chymotrypsin hydrolysis. The glycoprotein is much more resistant to proteolysis than the large chain. This differential susceptibility to proteolysis is not due to differences in the number of trypsin or chymotrypsin sensitive bonds because the two subunits are equally susceptible to proteolysis after isolation by preparative gel electrophoresis in sodium dodecyl sulfate. It is also not due to steric "shielding" of the glycoprotein by the large chain or its proteolytic products: (1) The rate of digestion of the glycoprotein is not increased after 90% of the large chain is digested. (2) The majority of the large chain peptides are released into the supernatant upon degradation. It is concluded that the greater resistance of the glycoprotein to proteolysis is due to its native conformation. In the absence of the large chain, the susceptibility of the glycoprotein to tryptic degradation by K+ and Na+. The evidence suggests that this decreased susceptibility was due to conformational changes in the glycoprotein. These specific ligand effects on proteolysis of the glycoprotein suggests that the glycoprotein may participate in Na+ and K+ binding by (Na+, K+)-ATPase.

Adenosine Triphosphatases↗
PubMed1987

Effects of industrial organic solvents on human erythrocyte membrane adenosine triphosphatase activities in vitro.

The effects of some aromatic hydrocarbons, aliphatic chlorinated hydrocarbons, and alcohols on adenosine triphosphatase (ATPase) activity in human erythrocyte ghost membrane were studied in vitro. Both aromatic and chlorinated aliphatic hydrocarbons inhibited this activity dose-dependently, the inhibition of total ATPase activity being clearer than that of magnesium-activated ATPase. Of the alcohols studied, methanol had no effect on the ATPase activity, but ethanol, propranolol, and butanol were slightly enzyme-activating at high concentrations. The enzyme-inhibiting potency of organic solvents was generally related to their lipid solubilities, but 1,1,2,2-tetrachloroethane was a potent enzyme inhibitor despite its low lipid solubility. This findings indicates that, eg, the molecular structure of solvents may modulate their enzyme inhibition. In the presence of Triton-X-100, toluene did not cause any changes in the activity of total ATPase, and the combined effect of the two compounds was slight. Triton-X-100 also caused a significant solubilization of membrane proteins although even the highest toluene concentrations did not. These results show that organic solvents may cause their membrane effects by acting directly on membrane-bound integral proteins such as ATPase. This action is not only dependent on the lipid solubility of the compounds, but also on their molecular structure.

Adenosine Triphosphatases↗
PubMed1978

The properties of adenosine triphosphatase from exponential and synchronous cultures of Alcaligenes eutrophus H16.

The properties of Alcaligenes eutrophus ATPase (adenosine triphosphatase) were investigated by using subcellular fractions prepared from cells growing in exponential and synchronous cultures. Both the soluble and membrane-bound forms of the ATPase were inhibited non-competitively (K(i) 142mum) by Nbf-Cl (4-chloro-7-nitrobenzofurazan), whereas only the membrane-bound enzyme was inhibited (non-competitive; K(i) 750mum) by NN'-dicyclohexylcarbodi-imide. Neither the activity of the ATPase nor its sensitivity to these two inhibitors varied during exponential growth. However, marked variations in ATPase activity were observed during synchronous growth, which were characterized by maxima at approx. 0.4 and 0.9 of a cell cycle and minima at approx. 0.1 and 0.6 of a cycle. Sensitivity to Nbf-Cl and NN'-dicyclohexylcarbodi-imide also varied during the cell cycle; maximum inhibition by the former occurred at approx. 0.4 and 0.9 of a cell cycle, whereas maximum inhibition by the latter was located at approx. 0.1 and 0.6 of a cell cycle. Proton conductance by whole cells was also periodic during the cell cycle, the lowest rates occurring at approx. 0.15 and 0.55 of a cycle and the highest rates at approx. 0.4 and 0.9 of a cycle, but -->H(+)/O quotients for the oxidation of endogenous substrates remained relatively constant and indicated the presence of four proton-translocating respiratory segments throughout the cell cycle. These results are discussed in terms of ATPase and respiratory-chain structure and function during the cell cycle of Alcaligenes eutrophus.

4-Chloro-7-nitrobenzofurazan↗
PubMed1980

Role of the subunits of the energy-transducing adenosine triphosphatase from Micrococcus lysodeikticus membranes studied by proteolytic digestion and immunological approaches.

An energy-transducing adenosine triphosphatase (ATPase, EC 3.6.1.3) that contains an extra polypeptide (delta) as well as three intrinsic subunits (alpha, beta, gamma) was purified from Micrococcus lysodeikticus membranes. The apparent subunit stoichiometry of this soluble ATPase complex is alpha 3 beta 3 gamma delta. The functional role of the subunits was studied by correlating subunit sensitivity to trypsin and effect of antibodies raised against holo-ATPase and its alpha, beta and gamma subunits with changes in ATPase activity and ATPase rebinding to membranes. A form of the ATPase with the subunit proportions 1.67(alpha):3.00(beta:0.17(gamma) was isolated after trypsin treatment of purified ATPase. This form has more than twice the specific activity of native enzyme. Other forms with less relative proportion of alpha subunits and absence of gamma subunit are not active. Of the antisera to subunits, only anti-(beta-subunit) serum shows a slight inhibitory effect on ATPase activity, but its combination with either anti-(alpha-subunit) or anti-(gamma-subunit) serum increases the effect. The results suggest that beta subunit is required for full ATPase activity, although a minor proportion of alpha and perhaps gamma subunit(s) is also required, probably to impart an active conformation to the protein. The additional polypeptide not hitherto described in Micrococcus lysodeikticus ATPase had a molecular weight of 20 000 and was found to be involved in ATPase binding to membranes. This 20 000-dalton component can be equated with the delta subunit of other energy-transducing ATPases and its association with the (alpha, beta, gamma) M. lysodeikticus ATPase complex appears to be dependent on bivalent cations. The present results do not preclude the possibility that the gamma subunit also plays a role in ATPase binding, in which, however, the major subunits do not seem to play a role.

Adenosine Triphosphatases↗
PubMed1976

Assembly of the sarcoplasmic reticulum. Biosynthesis of the adenosine triphosphatase in rat skeletal muscle cell culture.

Temporal patterns of biosynthesis of the Ca2+ + Mg2+-dependent adenosine triphosphatase of sarcomplasmic reticulum were obtained from studies with primary cultures of rat skeletal muscle cells. Rates of synthesis at various stages of differentiation were estimated from the incorporation of tritium-labeled leucine into the ATPase. Cells were solubilized with detergent, and newly synthesized ATPase was isolated from cells by antibody precipitation in the presence of carrier ATPase. Radioactivity incorporated into the ATPase was determined after gel electrophoresis of the precipitates and counting of gel slices containing the ATPase band. In Dulbecco's modified Eagle's medium containing 10% horse serum and 0.5% chick embryo extract, mononucleated myoblast cells began to form multinucleated myotubes after about 50 hours in culture. Prior to fusion little ATPase synthesis was detectable; during fusion the ATPase was synthesized at an accelerating rate for a period of about 30 hours. The rate of synthesis levelled off after about 90 hours coincident with termination of fusion. In Dulbecco's modified Eagle's medium containing 20% fetal calf serum and 8% embryo extract, the onset of fusion was delayed for 30 to 40 hours. In this medium biosynthesis of the ATPase was also delayed so that biosynthesis of the ATPase appeared to be correlated with fusion of muscle cells. Cells cultured in Culbecco's modified Eagle's medium containgin 10% horse serum, but only 60 muM Ca2+, proliferated but did not fuse. Under these conditions, synthesis of the ATPase was measurable at 50 to 60 hours, and the rate of synthesis accelerated until 120 hours when it declined. Under all conditions degradation of the ATPase occurred with a half-life of 20 hours whereas the half-life of total protein degradation was 40 hours. Synthesis of the sarcoplasmic reticulum ATPase, like that of a number of other muscle-specific proteins, is greatly accelerated as myoblasts fuse and differentiate into myotubes. Fusion is not essential for this phenomenon, however, although it is normally concomitant with it.

Adenosine Triphosphatases↗
PubMed1997

Modifications induced by insulin-dependent diabetes mellitus on human placental Na+/K+-adenosine triphosphatase.

The causes of the reduced activity of Na+/K+-adenosine triphosphatase (ATPase) in human diabetes are still the object of controversy. The aim of this work was to investigate the mechanisms of inhibition by means of the study of the Na+/K+-ATPase purified from human placenta. We purified Na+/K+-ATPase from term placentas of six healthy women and six age-matched women with insulin-dependent diabetes mellitus (IDDM) in good metabolic control. The enzymatic activity was reduced in both the microsomal fraction and the purified Na+/K+-ATPase obtained from diabetic women, whereas no difference was found in the number of active molecules determined by anthroyl ouabain binding. The Na+/K+-ATPase purified from women with IDDM did not show any modification in the ouabain affinity or changes in the physicochemical structure of the ouabain binding site investigated by dynamic fluorescence or alterations in lateral diffusion. The activation energy of the enzyme was increased, whereas the tryptophan accessibility of the enzyme was lower in women with IDDM. The fluidity of the lipid anulus of the enzyme was higher in women with IDDM than in control women, as suggested by fluorescence polarization of 1-(4-trimethylaminophenyl)-6-phenyl-1,3,5-hexatriene. The adenosine triphosphate-binding site, investigated by anisotropy decay studies of the fluorescent probe pyrene isothiocyanate, was modified in women with IDDM. It appears that the Na+/K+-ATPase of human placenta is altered in its disposition in IDDM.

Acrylamide↗
PubMed1984

High affinity, calcium-stimulated adenosine triphosphatase activity in the particulate fraction of rat pancreatic acini.

Adenosine triphosphatase activity which is Mg2+-dependent and stimulated by submicromolar concentrations of Ca2+ (as Ca . ATP) was identified in the total particulate fraction of rat pancreatic acini. Half-maximal activity (V0.5) is obtained at 100.1 +/- 6 nM Ca . ATP with a Hill coefficient of 2.2 +/- 0.1 (mean +/- S.E.; n = 4). Maximal activity was 75 +/- 19 pmol of Pi released from ATP minute-1 microgram of membrane protein-1 (mean +/- S.E.; n = 7). High affinity Ca2+-ATPase activity was unaffected by ouabain, Na+, K+, La3+, and added calmodulin. Activity was slightly reduced by ruthenium red (0.1 mM) and by oligomycin (80 micrograms/ml) but was reduced almost 50% by the phenothiazine derivative fluphenazine in a dose-related and Ca2+-dependent manner. Hydrolysis of p-nitrophenyl phosphate was 9% of the rate of ATP hydrolysis and was independent of Ca2+ concentration. However, ADP, GTP, UTP, and ITP were hydrolyzed at 76-93% the rate that ATP was hydrolyzed with V0.5 values and Hill coefficients similar to those of Ca . ATP. We conclude that rat pancreatic acini contain an enzyme for active Ca2+ translocation: ATPase activity that is Mg2+-dependent and stimulated by submicromolar concentrations of Ca . ATP. Substrate hydrolysis appears to involve positive cooperative interactions of multiple ligand-binding sites and may be regulated in part by calmodulin.

Adenosine Triphosphate↗
PubMed1983

Na+- and K+-dependent adenosine triphosphatase changes in multiple sclerosis plaques.

Na+- and K+-dependent adenosine triphosphatase [(Na+ + K+)-ATPase] was studied in microdissected samples from sections of histologically active and inactive plaques of multiple sclerosis. In active plaques the enzyme was found to be markedly reduced in activity, whereas in old, chronic plaques ATPase activities were higher than those of unaffected white matter. White matter from control patients and normal-appearing white matter from MS patients did not differ with regard to ATPase activities. The results suggest that reversible changes in the sodium pump mechanism may be involved in the pathophysiology of multiple sclerosis.

Brain↗
PubMed1993

Calcium modulates the influence of length changes on the myofibrillar adenosine triphosphatase activity in rat skinned cardiac trabeculae.

The relationship between adenosine triphosphate (ATP) turnover and muscle performance was investigated in skinned cardiac trabeculae of the rat at different [Ca2+] and two different sarcomere lengths (1.8 microns and 2.2 microns) at 20 degrees C. ATP turnover was measured photometrically by enzymatic coupling of the regeneration of ATP to the oxidation of reduced nicotinamide adenine dinucleotide. The trabeculae were studied under isometric conditions and when the length was altered repetitively at a frequency of 23 Hz, with a square wave, by 5% of the initial length. The isometric ATPase activity amounted to 0.48 mM/s. Isometric ATP turnover and force were proportional at different [Ca2+]. During length changes at maximal activation (pCa 4.27) and 2.2 microns sarcomere length, ATPase activity increased to up to 162% whereas at low [Ca2+], ATPase activity decreased with respect to the isometric value at that pCa. At pCa 5.5, ATPase activity was reduced to 33%. These results indicate that during the length changes the apparent cross-bridge detachment rate is increased and the apparent attachment rate is decreased. The findings suggest that the Fenn effect, i.e. the increase in energy turnover above the isometric value during shortening, is present in cardiac trabeculae at high levels of activation, but is absent or reversed at lower levels of activity.

Adenosine Triphosphatases↗
PubMed1993

Identification of proton-translocating adenosine triphosphatases in rat cerebral microvessels.

To determine if proton translocating adenosine triphosphatases (ATPases) can be localized at the blood-brain barrier, isolated rat cerebral microvessels and cerebral synaptosomal preparations were assayed for ATPase activity in the presence of various inhibitors. N-ethylmaleimide-sensitivity could be consistently found in both cerebral microvessel and synaptosomal preparations. There was no vanadate sensitive component in the presence of ouabain, oligomycin and EGTA. Immunoblotting of cerebral microvessels and synaptosomes with a monoclonal antibody (E11) against the 31 kDa subunit of the vacuolar type H-ATPase pump identified a discrete 31 kDa band. Diffuse immunocytochemical staining of cerebral cortical tissue, predominantly in choroid plexus, could be found with E11 but not with HK alpha N2, an H,K-ATPase specific antibody, nor with a non-specific mouse monoclonal antibody (MOPC-21). Immunoblotting with HK alpha N2 showed an immunoreactive 76 kDa band, not present with the preimmune serum or the antibody preabsorbed with the immunizing synthetic peptide. It is concluded that the vascular type H-ATPase and not the gastric H,K-ATPase is present in cerebral tissue including cerebral microvessels and choroid plexus. Non-specific immunoreactivity may account for the 76 kDa band observed in the immunoblots using the HK alpha N2 antibody although presence of a degradation product of H,K-ATPase can not be ruled out. The functional role of the vacuolar H-ATPase in the blood-brain barrier remains to be determined.

Animals↗
PubMedDate not supplied

Differences in renal tubular Na-K-adenosine triphosphatase in spontaneously hypertensive and normotensive rats.

Na-K-adenosine triphosphatase (ATPase) activity in seven specific renal tubular segments of 8-week-old spontaneously hypertensive rats (SHR) was compared with age-matched normotensive Wistar-Kyoto rats (WKY). Systolic blood pressure in 8-week-old SHR were significantly higher than in age-matched WKY. Na-K-ATPase activity in proximal convoluted tubule and outer and inner medullary collecting ducts was significantly higher in SHR than in WKY. On the other hand, medullary thick ascending limbs had reduced Na-K-ATPase activity in SHR. The possible role of the abnormal pattern of renal tubular Na-K-ATPase in the development of hypertension in SHR remains to be determined.

Animals↗
PubMed1989

Active proton secretion and potassium absorption in the rabbit outer medullary collecting duct. Functional evidence for proton-potassium-activated adenosine triphosphatase.

We examined the hypothesis that proton-potassium-activated adenosine triphosphatase (H-K-ATPase) mediates K absorption and acidification in the inner stripe of the outer medullary collecting duct (OMCDi). Rabbits were fed a low-K diet (0.55% K) for 7-14 d because we have demonstrated previously that this low-K diet stimulates K-absorptive flux by the OMCDi. Proton secretion was measured as net total CO2 flux (JTCO2) by microcalorimetry. After basal collections, either vehicle or an inhibitor of gastric H-K-ATPase, omeprazole (0.1 mM), was added to the perfusate during the second period. Addition of vehicle to the perfusate changed neither the transepithelial voltage (VT, in millivolts) nor the JTCO2. In contrast, the addition of omeprazole (0.1 mM) to the perfusate abolished JTCO2 (from 14.5 +/- 5.6 to -0.1 +/- 3.1 pmol.mm-1.min-1) without significantly affecting VT. In additional experiments, in 16 tubules there was significant net K absorption (JK) of 5.0 +/- 1.0 pmol.mm-1.min-1 during the basal period, which exceeded the rate of K absorption that could be attributed to a paracellular voltage-mediated pathway (JKP = 1.0 +/- 0.4 pmol.mm-1.min-1, P less than 0.01). Administration of vehicle did not significantly affect either VT or JK. However, omeprazole abolished JK (from 5.1 +/- 1.0 to 0.1 +/- 2.5 pmol.mm-1.min-1) without affecting VT or JNa. The present results demonstrate that the OMCDi possesses an active, omeprazole-sensitive acidification and K-absorptive mechanism. These findings are consistent with the presence of H-K-ATPase activity in this nephron segment.

Absorption↗
PubMed1984

Immunocytochemical localization of Na+,K+ adenosine triphosphatase in the rat retina.

Immunocytochemical localization of Na+,K+-adenosine triphosphatase (ATPase) in fixed sections of rat retina was carried out using polyclonal antibodies to the highly purified enzyme and peroxidase-antiperoxidase and immunofluorescence techniques. In the photoreceptor layer of the rat retina, Na+,K+-ATPase immunoreactive sites were associated primarily with inner segments and only background activity was associated with the outer segments. This localization supports the proposed distribution of Na+,K+-ATPase in photoreceptor cells suggested by physiological studies. The Na+,K+-ATPase immunoreactive sites were also localized in the inner and outer plexiform layers, which are rich in synaptic contacts. The reticular pattern of immunostaining in those regions suggests that Na+,K+-ATPase immunoreactivity is associated with neuronal processes in those layers.

Animals↗
PubMed1999

Linkage and association of the sodium potassium-adenosine triphosphatase alpha2 and beta1 genes with respiratory quotient and resting metabolic rate in the Québec Family Study.

The purpose of this study was to examine the relationship between the alpha2 (exon 1 and exon 21-22 with BglII) and beta1 (MspI and PvuII) genes of the sodium potassium adenosine triphosphatase and resting metabolic rate (RMR) and respiratory quotient (RQ). The sample included 582 participants from 171 families of the Québec Family Study. RMR and RQ were adjusted for age, sex, fat mass, and fat free mass. Sib-pair analyses indicated a significant linkage between RQ and the alpha2 exon 1 marker (P = 0.03) and the alpha2 exon 21-22 marker (P = 0.02). No linkage was detected between the beta1 markers and either RMR or RQ, whereas RMR was not linked with the alpha2 makers. There was a significant interaction (P < 0.0003) between alpha2 exon 1 carrier status and age group [younger (< 45 yr) vs. older (> or = 45 yr) adults] for RQ. The association between carrier status and RQ was significant in younger adults (RQ = 0.76 in carriers vs. 0.80 in noncarriers, P < 0.0001) but was not in older adults (RQ = 0.81 in carriers vs. 0.80 in noncarriers). The alpha2 exon 1 gene accounted for approximately 9.1% and 0.3% of the variance in RQ in younger and older adults, respectively. The results suggest that the sodium potassium adenosine triphosphatase alpha2 gene may play a role in fuel oxidation, particularly in younger individuals.

Adolescent↗
PubMed1993

Aquastatin A, an inhibitor of mammalian adenosine triphosphatases from Fusarium aquaeductuum. Taxonomy, fermentation, isolation, structure determination and biological properties.

A new inhibitor of mammalian adenosine triphosphatases, designated aquastatin A, has been isolated from a fungus identified as Fusarium aquaeductuum. The structure of this compound has been determined by MS and NMR analyses. It inhibits Na+/K(+)-ATPase with an IC50 value of 7.1 microM, and H+/K(+)-ATPase with an apparent IC50 value of 6.2 microM.

Adenosine Triphosphatases↗