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Query: UNIPROT:P20020 (adenosine triphosphatase)
 3,299 document(s) hit in 31,850,051 MEDLINE articles (0.00 seconds)

Rat liver plasma membranes contained two types of calcium-dependent adenosine triphosphatase (Ca2+-ATPase, EC 3.6.1.3) activities. One of them had a high affinity for free calcium (Ca2+) with an apparent half maximal saturation constant (K0.5) of 0.2 microM (high affinity Ca2+-ATPase), and the other exhibited a low affinity with a K0.5 of 50 microM for Ca2+ (low affinity Ca2+-ATPase). The high affinity Ca2+-ATPase showed: independence from free magnesium (Mg2+), a wide range of optimum pH (7.2-7.5), inhibition by a large amount of calmodulin, and substrate preference for ATP, GTP and ITP. On the other hand, the low affinity Ca2+-ATPase showed: stimulation by Mg2+ as well as Ca2+, an optimum pH of 8, mild stimulation by calmodulin, reversible inhibition by calmodulin-antagonists, inhibition by dicyclohexylcarbodiimide, and substrate preference for UTP and GTP. Both Ca2+-ATPases were insensitive to Na+, K+, ouabain, NaN3 and KCN. Orthovanadate, a potent inhibitor for many ATPases, had no effect on both ATPases over a wide range of concentrations (7 nM-1.7 mM). The Ca2+-ATPases could be separated by gel filtration on a Sepharose 4B column after solubilization with Triton X-100. The high affinity Ca2+-ATPase showed a Stokes radius of about 49 A and a sedimentation coefficient of about 7.0 S with a molecular weight of 1.4 X 10(5). The frictional ratio was 1.4. The results suggest that the high affinity Ca2+-ATPase may be a possible candidate for an ATPase with Ca2+ pumping activity, and that the high affinity enzyme is distinct from the low affinity Ca2+-ATPase in the rat liver plasma membranes.
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PMID:Comparison of high affinity Ca2+-ATPase and low affinity Ca2+-ATPase in rat liver plasma membranes. 622 49

The sensitivity of RBC membrane (RBCM) Ca2+-adenosine triphosphatase (Ca2+-ATPase) to calmodulin stimulation was repeatedly studied in healthy volunteers and in 12 patients with affective disorders. Whereas control response was relatively stable, the patients showed great variability. This phenomenon was not due to formation of resealed vesicles in the RBCM nor to the quantity of calmodulin remaining in the RBCM preparations present in the cells before hemolysis. Changes in calmodulin sensitivity did not correlate with changes of mood or of drug treatment. When Ca2+-ATPase was relatively unresponsive to calmodulin, considerable enzyme activity was maintained at low calcium concentrations without calmodulin. In samples showing a large response to calmodulin, virtually no enzyme activity was detected at low calcium concentrations without exogenous calmodulin. Thus, calcium dependence and calmodulin sensitivity of the Ca2+-ATPase appeared to correlate positively with each other. As a similar phenomenon has been linked to changes in the composition of membrane phospholipids responsible for the regulation of Ca2+-ATPase activity, variations in baseline activity and calmodulin-induced stimulation of this enzyme may represent a fundamental defect in systems regulating membrane phospholipid composition.
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PMID:Sensitivity of RBC membrane Ca2+-adenosine triphosphatase to calmodulin stimulation. Variations in patients with bipolar affective disorders. 623 7

Calmodulin and calcium effects on cardiac ouabain-sensitive adenosine triphosphatase (ATPase) activity were studied in young spontaneously hypertensive rats (SHR) and in their normotensive control Wistar-Kyoto rats (WKY). Cardiac sarcolemmal membranes from SHR showed significantly higher ouabain-sensitive ATPase activity than membranes from WKY rats. This activity was unaffected by calmodulin or calcium alone. However, when both calmodulin and calcium were added, ouabain-sensitive activity was significantly reduced without changes in the total ATPase activity. The calcium-dependent calmodulin effect was dose-dependent and greater in SHR than in WKY membranes. An altered interaction between the calcium-calmodulin system and sodium handling by the plasma membrane in SHR may play a role in the pathogenesis of hypertension.
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PMID:Calmodulin reduces ouabain-sensitive ATPase of cardiac sarcolemmal membranes: high reduction in spontaneously hypertensive rats. 623 30

Red blood cell (RBC) calcium level had been found to be higher in women than in men. This study was designed to evaluate whether this is a general phenomenon and to elucidate a possible mechanism for a gender-related difference in RBC calcium levels. Differences in RBC calcium levels between women and men were examined in normal subjects, in patients with chronic renal failure (CRF) who were known to have elevated RBC calcium levels, and in female and male rats. RBC calcium level was higher in healthy women (6.1 +/- 0.5 mumol/L in women vs 4.4 +/- 0.3 mumol/L in men; p < 0.01), in women with CRF (45.8 +/- 11.8 mumol/L vs 15.4 +/- 1.1 mumol/L in men with CRF; p < 0.025) and women undergoing hemodialysis treatment (43.4 +/- 4.7 mumol/L vs 8.8 +/- 0.9 mumol/L in men undergoing hemodialysis p < 0.001). RBC calcium levels in female rats were also significantly higher than those in male rats. Ovariectomy reduced RBC calcium levels in female rats to those of male rats, whereas castration of male rats had no effect on RBC calcium levels. These in vivo findings suggest that the elevated RBC calcium level is associated with activity of female sex hormones. To investigate a possible mechanism, the in vitro effect of beta-estradiol on calcium 45 influx into RBCs and its effect on basal and calmodulin-stimulated Ca adenosine triphosphatase (CaATPase) activity in RBC membranes was determined. CaATPase activity was not affected by beta-estradiol at various concentrations and different incubation periods.(ABSTRACT TRUNCATED AT 250 WORDS)
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PMID:Red blood cell calcium level is elevated in women: enhanced calcium influx by estrogens. 844 97

The strong enzyme histochemical reactions for adenosine triphosphatase (ATPase) seen in ependymal tanycytes after incubation in calcium-containing media have previously been reported as calcium transport ATPase. Investigation of these reactions showed that: (1) any nucleoside triphosphate can serve as a substrate; (2) diphosphates and monophosphates cannot replace triphosphates; this includes p-nitrophenyl phosphate which is readily hydrolysed by plasma membrane transport ATPases; (3) strong localization occurs in the presence of millimolar concentrations of either calcium or magnesium ions; there is no absolute requirement for calcium ions; (4) they are not inhibited by sulphydryl inhibitors or calmodulin antagonists; (5) lead phosphate precipitates are localized almost entirely on the external face of tanycyte plasma membranes. In addition, the technique gives strong localization to vessels in the choroid plexus but not to the choroidal epithelium. Immunohistochemistry with a primary antibody raised against Ca2+, Mg2(+)-ATPase stains the choroidal epithelium but not the vessels or the ependymal tanycytes. These results are inconsistent with identification of the reaction as calcium transport ATPase but support characterization as an ecto-ATPase.
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PMID:Adenosine triphosphate-lead histochemical reactions in ependymal epithelia of murine brains do not represent calcium transport adenosine triphosphatase. 849 73

This review focuses on the physiological role of the plasma membrane Ca(2+)+ Mg(2+)-dependent adenosine triphosphatase (PM Ca(2+)-ATPase) in cellular signalling. Particular attention has been paid to the regulation of the PM Ca(2+)-ATPase (PM Ca2+ pump) by calmodulin, proteases, protein kinases, acidic phospholipids and oligomerization in intact cells. We also review recent work investigating the possible regulation of the PM Ca2+ pump by G proteins and agonists. The source of adenosine triphosphate (ATP) and Ca2+ in fueling and activating the Ca2+ pump is discussed, as well as the possible role of the PM Ca(2+)-ATPase in subplasma membrane Ca2+ regulation. The physiological implication of the localisation of the PM Ca2+ pump in caveolae is also considered.
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PMID:The plasma membrane calcium pump--a physiological perspective on its regulation. 874 45

The in vitro effect of okadaic acid on basal phorbol 12-myristate 13-acetate (PMA)-, and cyclic adenosine monophosphate (cAMP)-stimulated Mg(2+)-dependent Ca(2+)-adenosine triphosphatase (ATPase) activity in synaptosomal membranes isolated from rat brain cortex and cerebellum was investigated. The basal activity was enhanced by okadaic acid in both examined regions. This inhibitor differed in the regulation of Mg2+, Ca(2+)-ATPase activity in PMA- and cAMP-incubated membranes. Stimulation by calmodulin (CaM) of basal Mg2+, Ca(2+)-ATPase activity declined in cortex and cerebellum after treatment with okadaic acid. The presence of PMA or cAMP decreases the stimulatory effect of CaM. These results suggest that Mg2+, Ca(2+)-ATPase activity in the rat-brain synaptosomal membrane may be regulated in vitro by dephosphorylation processes.
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PMID:Okadaic acid as a probe for regulation in vitro of Mg(2+), Ca(2+)-ATPase activity in rat cortical and cerebellar synaptosomal membranes. 895 47

The regulatory myosin light chain (MLC) is phosphorylated in cardiac muscle by Ca2+/calmodulin-dependent MLC kinase (MLCK) and is considered to play a modulatory role in the activation of myofibrillar adenosine triphosphatase (ATPase) and the process of force generation. Since the depression in cardiac contractile function in chronic diabetes is associated with a decrease in myofibrillar ATPase activity, we investigated changes in MLC phosphorylation in diabetic heart. Rats were made diabetic by injecting streptozotocin (65 mg/kg intravenously), and the hearts were removed 8 weeks later; some 6-week diabetic animals were injected with insulin (3 U/d) for 2 weeks. Changes in the relative MLC and MLCK protein contents were measured by electrophoresis and immunoblot assay, whereas phosphorylated and unphosphorylated MLCs were separated on 10% acrylamide/urea gel and identified by Western blot. MLC and MLCK contents were decreased markedly (40% to 45%) and MLC phosphorylation was decreased significantly (30% to 45%) in the diabetic rat heart homogenate in comparison to control values. The changes in MLC and MLCK content in diabetic heart were partially reversible, whereas changes in MLC phosphorylation were normalized upon treatment with insulin. These results suggest that decreased protein contents of MLC and MLCK and phosphorylation of MLC may contribute to the depression of cardiac myofibriliar ATPase activity and heart dysfunction in diabetic cardiomyopathy.
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PMID:Myosin light-chain phosphorylation in diabetic cardiomyopathy in rats. 900 73

The present study was performed to investigate the effects of propiverine hydrochloride (1-methyl-4-piperidyl diphenylpropoxyacetate hydrochloride, P-4), a novel anti-pollakiuric agent, on the contractile proteins of smooth muscle. P-4 (30-300 microM) inhibited the activity of native actomyosin adenosine triphosphatase (ATPase) that had been freshly purified from canine urinary bladder, and calmodulin at 10 microM overcame this inhibition. P-4 also inhibited myosin light chain kinase from smooth muscle in a dose-dependent manner. However, at 300 microM, P-4 was unable to inhibit by 50% the activity of trypsin-treated myosin light chain kinase, which was independent of Ca2+/calmodulin. 1 mol of calmodulin bound 4 to 5 mol of [14C]P-4 in a Ca2+-dependent manner with a K(d) of 77.4 microM. These results indicate that calmodulin is one of the intracellular target molecules for P-4 and that inhibition of the action of calmodulin by P-4 might cause the inhibition of actomyosin ATPase activity, with subsequent relaxation of the smooth muscle of the urinary bladder.
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PMID:Propiverine hydrochloride, an anti-pollakiuric agent, inhibits the activity of actomyosin ATPase from the urinary bladder. 931 66

TRPC1 is a membrane protein that is highly conserved in mammals, amphibians and birds. It is widely expressed in cells throughout the body including in the heart and nervous system. Amino acid sequence analysis and over-expression studies indicate it is an ion channel that allows the transmembrane flux of small cations including sodium and calcium. In some cell types it is apparent that at least a fraction of TRPC1 exists in the plasma membrane. Inhibition of TRPC1 expression or block by TRPC1-specific antibody leads to attenuation of the plasma membrane calcium influx that occurs in response to depletion of calcium levels in sarcoplasmic or endoplasmic reticulum. TRPC1 would, therefore, seem to be a key subunit of store-operated channels (SOCs). TRPC1 is, nevertheless, unlikely to act alone. There is good evidence that it can heteromultimerise with the related proteins TRPC4, TRPC5 and polycystin-2; a tetrameric arrangement is envisaged, but not demonstrated. Like its relative in Drosophila, TRPC1 looks likely to function in a signalplex, a protein complex including inositol 1,4,5-triphosphate (IP(3)) receptor, plasma membrane calcium-ATPase, caveolin-1 and calmodulin. Its localisation in membranes is punctate and associated with functionally discrete calcium signals. TRPC1's function may not only be linked to SOCs but also to other cellular events including the nuclear translocation of the NFAT transcription factor. There is still much to be learned about this fundamental protein.
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PMID:TRPC1 store-operated cationic channel subunit. 1276 88


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