Gene/Protein Disease Symptom Drug Enzyme Compound
Pivot Concepts: Gene/Protein Disease Symptom Drug Enzyme Compound   Target Concepts: Gene/Protein Disease Symptom Drug Enzyme Compound

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Query: EC:3.6.1.3 (ATPase)
65,361 document(s) hit in 31,850,051 MEDLINE articles (0.00 seconds)

Troponin C was isolated from the skeletal muscle of bullfrog (Rana catesbeiana), and its relative molecular mass was estimated to be 18,000 by SDS/polyacrylamide gel electrophoresis. In its amino acid composition, bullfrog troponin C was similar to that of the frog (Rana esculenta) but different from that of rabbit. Its ultraviolet spectrum was consistent with its amino acid composition. The ultraviolet difference spectrum of the Ca(2+)-loaded form vs. the metal-free form indicated that the single Tyr residue and some Phe residues in the bullfrog troponin C molecule were affected by the conformational change associated with Ca2+ binding. On electrophoresis in polyacrylamide gel in 14 mM Tris and 90 mM glycine, the metal-free and Mg(2+)-loaded forms migrated slower than the Ca(2+)-loaded form. The property is shared by rabbit troponin C but not parvalbumins or calmodulin. The ATPase activity of CDTA-treated myofibrils reconstituted with bullfrog troponin C showed the same Ca(2+)- and Sr(2+)-sensitivity as that of those reconstituted with rabbit troponin C. Bullfrog troponin C is, thus, physiologically the same as rabbit troponin C, in spite of several marked differences in their physicochemical properties.
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PMID:Preparation and characterization of troponin C from bullfrog skeletal muscle. 129 89

The effect of Ca++ mobilizing agonists arginine vasopressin and phenylephrine on Na+/H+ exchange was studied in freshly isolated hepatocytes and isolated perfused rat livers. The activity of Na+/H+ exchange was determined from the rate of H+ efflux, 22Na uptake and pHi recovery. Arginine vasopressin and phenylephrine stimulated H+ efflux and 22Na uptake in isolated rat hepatocytes and increased the rate of pHi recovery from acid-loaded hepatocytes. These effects were inhibited by amiloride. Arginine vasopressin- and phenylephrine-induced increases in H+ efflux were also dependent on extracellular Na+. Arginine vasopressin- and phenylephrine-induced increases in intracellular Ca++ concentration, H+ efflux, 22Na uptake and intracellular pH recovery were decreased in hepatocytes preloaded with the Ca(++)-buffering agent [bis-(2-amino-5-methylphenoxy)-ethane-N,N,N',N'-tetraacetic acid] (MAPTA). Na+/H+ exchange-dependent intracellular pH recovery from cytosolic acidification was stimulated by thapsigargin, which increases intracellular calcium concentration by inhibiting endoplasmic reticulum Ca++ ATPase. Arginine vasopressin- and phenylephrine-induced increases in intracellular pH recovery were not dependent on extracellular Ca++ and were inhibited by calmidazolium, a calmodulin inhibitor. Arginine vasopressin and phenylephrine also increased H+ efflux in the absence but not in the presence of amiloride in perfused rat livers without affecting biliary HCO3- excretion. These results indicate that arginine vasopressin and phenylephrine activate Na+/H+ exchange in rat hepatocytes, an effect mediated in part by intracellular Ca++ and calmodulin kinase. Furthermore, sinusoidal Na+/H+ exchange does not appear to be involved in biliary HCO3- excretion.
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PMID:Intracellular calcium-mediated activation of hepatic Na+/H+ exchange by arginine vasopressin and phenylephrine. 130 63

A 45 amino acid peptide (A45) corresponding to the phospholamban (PLN) binding domain of the sarcoplasmic reticulum (SR) ATPase was synthesized. Circular dichroism experiments have shown that the peptide had a predominantly random-coil conformation but adopted a higher proportion of secondary structure in the presence of a synthetic 32 amino acid peptide corresponding to the hydrophilic portion of PLN. A similar conformational change was induced by the synthetic calmodulin binding domain of the plasma membrane Ca2+ pump (peptide C28W), which acts as an endogenous inhibitor of the pump and is homologous to PLN. Cross-linking experiments have shown that peptide C28W interacted with peptide A45. The Ca(2+)-pumping activity of cardiac SR, which contains endogenous PLN, was stimulated about 30% by peptide A45. The stimulation was maximal at submicromolar Ca2+ levels and tended to disappear at higher Ca2+ concentrations. By contrast, the Ca(2+)-pumping activity of skeletal muscle SR, which lacks endogenous PLN, was unaffected. Peptide C28W strongly inhibited the pumping activity of skeletal muscle SR, and peptide A45 reversed the inhibition. The results suggest that peptide A45 competed with the ATPase for phospholamban or for peptide C28W, removing the inhibition of the pump. Thus, the exogenous inhibitor of the SR Ca(2+)-ATPase, PLN, and the internal inhibitor of the plasma membrane Ca(2+)-ATPase, peptide C28W, are functionally analogous.
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PMID:Regulation of the calcium ion pump of sarcoplasmic reticulum: reversible inhibition by phospholamban and by the calmodulin binding domain of the plasma membrane calcium ion pump. 131 37

Cellular calcium (Ca) exchange in arterially perfused whole heart is markedly perfusion-limited. Therefore, a large fraction of exchangeable Ca recycles within the cell before exchanging with extracellular Ca. Ca enters the cell via sarcolemmal (SL) transient (T) and long-lasting (L) channels activated at more negative and less negative membrane potential, respectively. The larger L currents are controlled via phosphorylation and G protein interaction to provide Ca to induce Ca release from sarcoplasmic reticulum (SR) and for direct myofilament activation. Troponin C (TNC) binds 3 mol of Ca/mol. Only the low affinity site is responsible for activation of force and regulation of myofilament ATPase rate. This occurs through a shift in troponin I (TNI) with respect to actin induced by the TNC Ca binding. Relaxation depends on reduction of cytosolic (Ca) and occurs via 1) Ca pumping into the longitudinal SR modulated by phospholamban; 2) the recently cloned high-capacity electrogenic SL Na-Ca exchanger; and 3) the SL Ca pump under complex regulation including calmodulin control. Mitochondria transport Ca, but this transport is directed primarily to the regulation of various Ca-sensitive dehydrogenases so that oxidative metabolism can be adjusted to changes in energy demand. The regulation of Ca movements consumes about 25% of the cell's total energy output. Mitochondrial Ca exchanges with extracellular Ca most slowly (t 1/2 = 3.6 min), SR Ca quite rapidly (t 1/2's = 3 and 19 s), and an Na-Ca exchange-dependent compartment very rapidly (t 1/2 = 500 ms). After further description of Ca handling by the individual organelles, Ca movement is followed through the cell during the course of contraction, and the contribution of each organelle or compartment to overall cellular Ca exchange is defined.
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PMID:Calcium and the heart: exchange at the tissue, cell, and organelle levels. 131 Sep 47

The stimulation of the purified human erythrocyte calcium pump by acidic phospholipids was investigated using synthetic peptides corresponding to a putative phospholipid-responsive domain [Zvaritch, E., James, P., Vorherr, T., Falchetto, R., Modyanov, N. & Carafoli, E. (1990) Biochemistry 29, 8070-8076] and to the calmodulin-binding domain of the pump. The peptides interfered with the activation of the enzyme by phosphatidylserine and phosphatidic acid in competition assays. The peptide corresponding to the calmodulin-binding domain was found to be the most efficient antagonist. Direct binding measurements using fluorescent derivatives of the peptides confirmed the interaction between the acidic phospholipids and the peptides, and fluorescence titrations of dansylated calmodulin with the purified ATPase showed a direct effect of acidic phospholipids on calmodulin binding. A proteolyzed preparation of the Ca(2+)-ATPase lacking the calmodulin-binding domain confirmed that the phospholipid-induced stimulation is mediated by two sites, one located in the C-terminal portion of the previously identified 44-amino-acid phospholipid-responsive domain, the other in the calmodulin-binding domain.
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PMID:Identification of two domains which mediate the binding of activating phospholipids to the plasma-membrane Ca2+ pump. 131 84

Purified porcine erythrocyte membrane Ca(2+)-ATPase and 3':5'-cyclic nucleotide phosphodiesterase were stimulated in a dose-dependent, saturable manner with the vitamin D-dependent calcium binding protein from rat kidney, calbindin-D28k (CaBP-D28k). The concentration of CaBP-D28k required for half-maximal activation (K0.5 act.) of the Ca(2+)-ATPase was 28 nM compared to 2.2 nM for calmodulin (CaM), with maximal activation equivalent upon addition of either excess CaM or CaBP-D28k. 3':5'-Cyclic nucleotide phosphodiesterase (PDE) also showed equivalent maximum saturable activation by calbindin (K0.5 act. = 90 nM) or calmodulin (K0.5 act. = 1.2 nM). CaBP-D28k was shown to effectively compete with CaM-Sepharose for PDE binding. Immunoprecipitation with CaBP-D28k antiserum completely inhibited calbindin-mediated activation of PDE but had no effect on calmodulin's ability to activate PDE. While the physiological significance of these results remains to be established, they do suggest that CaBP-D28k can activate enzymes and may be a regulator of yet to be identified target enzymes in certain tissues.
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PMID:In vitro enzyme activation with calbindin-D28k, the vitamin D-dependent 28 kDa calcium binding protein. 131 45

Proteins in human red cell hemolysate were purified to determine which of them increase inhibition of the Na,K-ATPase in the presence of 2 microM free Ca. Samples purified 600,000-fold inhibited the Na,K-ATPase of human red cells in a Ca-dependent manner and stimulated the (Ca+Mg)-ATPase. These samples contained two proteins as analyzed by sodium dodecyl sulfate-polyacrylamide gel electrophoresis (SDS-PAGE): calmodulin (18,000 Mr), which comprised most (greater than 90%) of the total protein, and an unidentified protein of approximately 13,000 Mr. Both proteins were a distinctive light yellow when stained with silver. Calmodulin from bovine testes also inhibited the Na,K-ATPase and stimulated the (Ca+Mg)-ATPase. This preparation also contained two proteins as analyzed by SDS-PAGE: calmodulin (95 to 99% of the total protein) and another protein of approximately 13,000 Mr (1 to 5% of the total protein). Both were light yellow when stained with silver. Since the amount of red cell protein was limited, the remainder of the study was carried out with the bovine testes preparation. Heating the testes preparation decreased, but did not abolish, inhibition of the Na,K-ATPase and reduced stimulation of the (Ca+Mg)-ATPase. When corrected for denatured calmodulin, both heated and unheated proteins increased inhibition of the Na,K-ATPase to the same extent. The Na,K-ATPase was inhibited at 2 microM free Ca in a dose-dependent manner over a range of 15 to 100 nM calmodulin. To establish if the inhibition was due to the calmodulin or the 13,000 Mr protein, both were electroeluted after SDS-PAGE. Electroeluted calmodulin stimulated the (Ca+Mg)-ATPase and increased Ca inhibition of the Na,K-ATPase. Electroeluted amounts of the smaller Mr protein slightly stimulated the (Ca+Mg)-ATPase, but had no effect on the Na,K-ATPase. This protein was digested with cyanogen bromide, partially sequenced, and thereby identified as a fragment of calmodulin. We conclude that intact calmodulin increases inhibition of the Na,K-ATPase at 2 microM free Ca. We suggest that calmodulin is part of a mechanism mediating the effects of physiological free Ca on the Na,K-ATPase.
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PMID:Calmodulin increases Ca-dependent inhibition of the Na,K-ATPase in human red blood cells. 131 6

We studied the effect of muscle acylphosphatase on the Ca2+ pumping ATPase of heart sarcolemma. Acylphosphatase addition to calmodulin-depleted sarcolemmal vesicles produced a significant increase in the rate of Ca(2+)-dependent ATP hydrolysis, even higher than obtained with exogenously added calmodulin. Maximal stimulation (about four fold over basal value) was obtained with 550 units/mg vesicle protein, a concentration that fall within the physiological range. Conversely, similar amounts of acylphosphatase decreased the rate of ATP-dependent Ca2+ transport into the sarcolemmal vesicles. The maximal statistically significant inhibition of Ca2+ uptake was observed with the same acylphosphatase concentration that gave the maximal stimulation of Ca(2+)-ATPase activity. From these findings acylphosphatase appears to reduce the efficiency of heart sarcolemmal Ca2+ pump with an impairment of the coupling between ATP hydrolysis and Ca2+ transport. A possible mechanism of this effect is discussed.
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PMID:Alterations induced by acylphosphatase in the activity of heart sarcolemma calcium pump. 131 52

1. Calcium concentration and Ca(2+)-ATPase activity under basal conditions and after maximal stimulation with calmodulin were measured in erythrocytes from 32 patients with end-stage renal failure on haemodialysis and from 27 healthy subjects. 2. In patients with renal failure the Ca2+ concentration in erythrocytes was elevated compared with healthy subjects (4.27 +/- 1.02 versus 2.86 +/- 0.57 mumol/l, P less than 0.05). 3. Basal Ca(2+)-ATPase activity was lower in the patients with renal failure than in healthy subjects (4.62 +/- 1.34 versus 5.43 +/- 1.23 pmol of phosphate min-1 10(-6) erythrocytes). After maximal stimulation, Ca(2+)-ATPase activity reached 6.93 +/- 2.81 pmol of phosphate min-1 10(-6) erythrocytes in the patients with renal failure, whereas in healthy subjects stimulation yielded a Ca(2+)-ATPase activity of 32.54 +/- 8.48 pmol of phosphate min-1 10(-6) erythrocytes. 4. Incubation of erythrocytes from healthy subjects with plasma from uraemic patients caused inhibition of Ca(2+)-ATPase. Likewise, the ultrafiltrate from plasma obtained by haemofiltration treatment inhibited Ca(2+)-ATPase. 5. Gel chromatography of the ultrafiltrate and laser desorption/ionization mass spectroscopy revealed that a fraction containing substances with a molecular mass of about 300 Da inhibited Ca(2+)-ATPase. 6. It is concluded that, in uraemia, a Ca(2+)-ATPase inhibitor accumulates in the plasma, and this could contribute to the toxicity of uraemia by inhibiting cellular Ca2+ transport in erythrocytes and possibly other tissues.
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PMID:Isolation of an ultrafilterable Ca(2+)-ATPase inhibitor from the plasma of uraemic patients. 132 May 46

1. The effect of (Na+ + K+)-ATPase inhibitor ouabain (10(-5)-3 x 10(-4) M), and the (Ca2+ + Mg2+)-ATPase inhibitors vanadate (6 x 10(-6)-6 x 10(-4) M), oxytocin (2 x 10(-9)-4 x 10(-8) M, and prostaglandin F2 alpha (PGF2 alpha, 10(-7)-6 x 10(-6) M) were assayed on rat uterus incubated in Ca-free medium. 2. Vanadate, oxytocin and PGF2 alpha, but not ouabain, induced contractions in a dose-dependent way (ED50: 7.5 +/- 0.03 x 10(-5) M; 6.5 +/- 0.064 x 10(-9) M and 3.8 +/- 0.085 x 10(-7) M). 3. Vanadate (3 x 10(-4) M) and oxytocin (OT, 10 mU/ml = 2 x 10(-8) M)-induced tonic contraction were not modified by nifedipine (10(-10)-10(-6) M), monensin (10(-5)-3 x 10(-4) M) or amiloride (10(-5)-10(-3) M). 4. The intracellular calcium release inhibitors TMB-8 (10(-6)-10(-4) M) and dantrolene (3 x 10(-6)-10(-4) M), and the prostaglandin release inhibitor indomethacin (3 x 10(-8)-6 x 10(-5) M) relaxed the vanadate and OT-induced tonic contractions. 5. The calmodulin inhibitors trifluoperazine (3 x 10(-5)-3 x 10(-4) M), bepridil (10(-8)-3 x 10(-4) M), calmidazolium (10(-7)-10(-4) M) and W-7 (10(-7)-10(-5) M) also relaxed the vanadate and OT-induced tonic contractions. 6. Our results suggest that oxytocin and vanadate-induced contractions on rat uterus in Ca-free medium could be produced by release of prostaglandins and intracellular calcium, and mediated by calmodulin.
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PMID:Mediators involved in the rat uterus contraction in calcium-free solution. 132 41


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