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)

Regulation of the intestinal absorption of calcium by vitamin D in the rat involves the synthesis or maintenance of specific membrane proteins. A particulate preparation derived from duodenal mucosal homogenates or isolated microvillus membranes contains at least three vitamin D-dependent activities: calcium binding, p-nitrophenylphosphatase, and calcium-dependent ATPase. The membrane calcium-binding activity correlates closely with calcium transport. Solubilization and biochemical purification have led to the separation of the calcium-binding from the enzymatic activities and to the isolation of the calcium-binding protein (CaBP). This membrane protein has an apparent molecular weight of approximately 200,000 in 0.1% Triton X-100 and yields a monomeric subunit of molecular weight 20,500 in sodium dodecyl sulfate. The new protein, named IMCal, is clearly distinguished from the soluble CaBP found in mucosal homogenates and has a higher affinity for calcium than does the soluble protein. The hypothesis is proposed that IMCal is involved in the facilitated entry of calcium into the enterocyte from the lumen of the intestine.
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PMID:Isolation of the protein IMCal, a vitamin D-dependent membrane component of the intestinal transport mechanism for calcium. 705 1

Some markers of the intracellular systems that regulate neuronal activity and morphology were analyzed in the cerebral ganglion of hibernating snails (Helix aspersa), in comparison with active animals. The immunocytochemical expression of a calcium-binding protein, i.e. calmodulin, and some cytoskeletal components, i.e. 200 kDa phosphorylated neurofilament protein (pNFH), microtubule associated protein 2 (MAP2) and alpha-tubulin were analyzed by the use of a panel of antibodies raised against mammal antigens. Moreover, by enzymatic reactions the Ca(2+)-ATPase and alkaline phosphatase (AIPase) activities were demonstrated. In comparison with the active phase, the hibernation induced an increase in the immunopositivity for calmodulin in all the neurons. The increase may be linked to unmasking of immunoreactive epitopes due to conformational changes of the protein, which in turn may be a consequence of a reduction or absence of binding with calcium ions or of a real increase in the amount of calmodulin in the somata of neurons. In any event, both the hypotheses indicate that neurons have decreased or suppressed the Ca(2+)-dependent mechanisms as also shown by the lower Ca(2+)-ATPase activity. Nevertheless, the AIPase activity, which was localized in the epineural sheat, was not significantly changed during hibernation and this supports that some metabolic activities are preserved in the hibernated animals. Changes in the immunopositivity for cytoskeletal components were found. There was an increase in the epitopes recognized by the mammalian pNF antibody, that concerned both the positivity of the entire cytoplasm of some clusters of metacerebral neurons and the intensity of the reaction. This would be aimed to improve the stability of the somata and primary neurites. Moreover, the decrease of alpha-tubulin and MAP2 immunopositivity, suggests that a disassembly of microtubules have occurred. The findings indicate that the transport of vesicles in the axons is slowed down during hibernation. In fact, research in progress show that the patterns of neurotransmission and neuromodulation are also deeply modified.
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PMID:The cerebral neurons of Helix aspersa during hibernation. Changes in the cytochemical detection of calmodulin, cytoskeletal components and phosphatases. 753 46

The activating mechanism of regucalcin, a calcium-binding protein isolated from rat liver cytosol, on (Ca(2+)-Mg2+)-ATPase in the plasma membranes of rat liver was investigated. (Ca(2+)-Mg2+)-ATPase activity was markedly increased by a sulfhydryl (SH) group protecting reagent dithiothreitol (DTT; 2.5 and 5 mM as a final concentration), while the enzyme activity was significantly decreased by a SH group modifying reagent N-ethylmaleimide (NEM; 0.5-5 mM). The effect of DTT (5 mM) to increase the enzyme activity was clearly blocked by NEM (5 mM). Regucalcin (0.25-1.0 microM) significantly increased (Ca(2+)-Mg2+)-ATPase activity. This increase was completely blocked by NEM (5 mM). Meanwhile, digitonin (0.04%), which can solubilize the membranous lipids, significantly decreased (Ca(2+)-Mg2+)-ATPase activity. Digitonin did not have an effect on the DTT (5 mM)-increased enzyme activity. However, the effect of regucalcin (0.25 microM) increasing (Ca(2+)-Mg2+)-ATPase activity was entirely blocked by the presence of digitonin. The present results suggest that regucalcin activates (Ca(2+)-Mg2+)-ATPase by the binding to liver plasma membrane lipids, and that the activation is involved in the SH groups which are an active site of the enzyme.
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PMID:Activating effect of regucalcin on (Ca(2+)-Mg2+)-ATPase in rat liver plasma membranes: relation to sulfhydryl group. 785 34

Calponin inhibits actomyosin Mg2+ ATPase and is proposed to regulate smooth muscle contraction; however, the mechanism by which it exerts its effect and the regulation of its behavior is still under investigation. The proposed methods by which calponin regulation is effected include reversible phosphorylation of calponin which would allow contraction to occur and regulation by interaction with calcium-calmodulin. However, several investigators have been unable to find evidence of in vivo phosphorylation of calponin, and the affinity between calponin and calmodulin is not high enough to suggest that this interaction is biologically significant. In this paper, we present an alternative method of calponin regulation via calcium-caltropin and describe the calponin-caltropin complex for the first time. Caltropin, a calcium-binding protein isolated from smooth muscle, is a dimer under native conditions and interacts with calponin in a calcium-dependent fashion in the ratio of 2 mol of dimer: 1 mol of calponin. The formation of this complex can be monitored by following the fluorescence of an acrylodan label on cysteine 273 of calponin, which undergoes a 35-nm blue shift in wavelength peak from 505 to 470 nm when calponin becomes complexed with caltropin. This fluorescence change when titrated with calcium indicates that the concentration of calcium required for complex formation is approximately 10(-5) M, corresponding to the low-affinity calcium-binding sites of caltropin. This complex was further characterized by circular dichroism (CD).(ABSTRACT TRUNCATED AT 250 WORDS)
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PMID:Smooth muscle calponin-caltropin interaction: effect on biological activity and stability of calponin. 818 Jan 79

The effect of various metals and regucalcin, a calcium-binding protein isolated from rat liver cytosol, on (Ca(2+)-Mg2+)-ATPase activity in the plasma membranes of rat liver was investigated. Of various metals (Zn2+, Cu2+, Ni2+, Mn2+, Co2+ and Al3+; 100 microM as a final concentration), Mn2+ and Co2+ increased markedly (Ca(2+)-Mg2+)-ATPase activity, while other metals had no effect. When Ca2+ was not added into enzyme reaction mixture, Mn2+ and Co2+ (25-100 microM) did not significantly increase the enzyme activity, indicating that heavy metals act on Ca(2+)-stimulated phosphorylation of the enzyme. Meanwhile, regucalcin (0.25-1.0 microM) caused a remarkable elevation of (Ca(2+)-Mg2+)-ATPase activity. This increase was not inhibited by the presence of 100 microM vanadate, although the effects of Mn2+ and Co2+ (100 microM) were inhibited by vanadate. Also, the inhibition of the Mn2+ and Co2+ effects by vanadate was not seen in the presence of regucalcin. Moreover, regucalcin (0.5 microM) increased significantly the enzyme activity in the absence of Ca2+. This effect of regulcalcin was not altered by increasing concentrations of Ca2+ added, indicating that the regucalcin effect does not depend on Ca2+. The present results suggest that regucalcin activates directly (Ca(2+)-Mg2+)-ATPase in liver plasma membranes, and that the activation is not involved in the Ca(2+)-dependent phosphorylation of the enzyme.
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PMID:Regulatory effect of regucalcin on (Ca(2+)-Mg2+)-ATPase in rat liver plasma membranes: comparison with the activation by Mn2+ and Co2+. 823 87

It has become clear that calcium is an important mediator in the transduction of signals due to ligand binding to cell surface receptors. Cytosolic calcium is typically maintained at low levels in both muscle and non-muscle cells and intracellular sequestering of calcium appears to be important in this process. The identification of intracellular calcium pools has been the subject of much recent study, and it has been proposed that such pools would contain three components: a calcium-activated pump or Ca(2+)-ATPase, a calcium channel such as the inositol trisphosphate receptor or ryanodine receptor, and a high-capacity calcium-binding protein such as calsequestrin or calreticulin. We report here on the localization of two components, the organellar Ca(2+)-ATPase (SERCA) and calreticulin, in neuronal tissues. Using immunofluorescence and subcellular fractionation, we have found that for the most part, these two proteins do not co-localize in neuron cell bodies, dendrites, or axons; but may co-localize at the axon terminal.
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PMID:Differences in the subcellular localization of calreticulin and organellar Ca(2+)-ATPase in neurons. 838 14

The chicken eggshell supplies approximately 80% of the calcium found in the hatchling chick. The mobilization of eggshell calcium into the developing embryo involves the transepithelial transport of large amounts of calcium in a development-specific manner. The cells responsible for the transport of eggshell calcium into the embryonic circulation are the ectodermal cells of the chorioallantoic membrane. In this report, we present a method for the isolation and culture of chorioallantoic membrane ectodermal cells, which are amenable to direct experimental manipulation. Cell preparations are characterized with respect to the expression of an ectoderm-specific cell surface marker (transcalcin, a calcium-binding protein), and a specific enzymatic activity (elevated Ca(2+)-activated ATPase). Functional assessment of in vitro cellular calcium uptake by 45Ca2+ tracer kinetics indicates the persistence of a temperature-sensitive, rapid-influx pathway similar to that observed in vivo. The preparations of primary ectodermal cells present an in vitro system applicable to the experimental analysis of calcium metabolism and transport by the chick chorioallantoic membrane.
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PMID:Transepithelial calcium transport in the chick chorioallantoic membrane. I. Isolation and characterization of chorionic ectoderm cells. 840 71

Organelles in the axoplasm from the squid giant axon move along exogenous actin filaments toward their barbed ends. An approximately 235-kDa protein, the only band recognized by a pan-myosin antibody in Western blots of isolated axoplasmic organelles, has been previously proposed to be a motor for these movements. Here, we purify this approximately 235-kDa protein (p235) from axoplasm and demonstrate that it is a myosin, because it is recognized by a pan-myosin antibody and has an actin-activated Mg-ATPase activity per mg of protein 40-fold higher than that of axoplasm. By low-angle rotary shadowing, p235 differs from myosin II and it does not form bipolar filaments in low salt. The amino acid sequence of a 17-kDa protein that copurifies with p235 shows that it is a squid optic lobe calcium-binding protein, which is more similar by amino acid sequence to calmodulin (69% identity) than to the light chains of myosin II (33% identity). A polyclonal antibody to this light chain was raised by using a synthetic peptide representing the calcium binding domain least similar to calmodulin. We then cloned this light chain by reverse transcriptase-PCR and showed that this antibody recognizes the bacterially expressed protein but not brain calmodulin. In Western blots of sucrose gradient fractions, the 17-kDa protein is found in the organelle fraction, suggesting that it is a light chain of the p235 myosin that is also associated with organelles.
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PMID:An axoplasmic myosin with a calmodulin-like light chain. 865 Feb 20

The effect of regucalcin, a calcium-binding protein isolated from rat liver cytoplasm, on ATP-dependent calcium transport in the plasma membrane vesicles of rat liver was investigated. (Ca(2+)- Mg2+)-ATPase activity in the liver plasma membranes was significantly increased by the presence of regucalcin (0.1-0.5 microM) in the enzyme reaction mixture. This increase was completely inhibited by the presence of sulfhydryl group modifying reagent Nethylmaleimide (5.0 mM NEM) or digitonin (0.04%), which can solubilize the membranous lipids. When ATP-dependent calcium uptake by liver plasma membrane vesicles was measured by using 45CaCl2, the presence of regucalcin (0.1-0.5 microM) in the reaction mixture caused a significant increase in the 45Ca2+ uptake. This increase was about 2-fold with 0.5 microM regucalcin addition. An appreciable increase was seen by 5 min incubation with regucalcin addition. The regucalcin-enhanced ATP-dependent 45Ca2+ uptake by the plasma membrane vesicles was completely inhibited by the presence of NEM (5.0 mM) or digitonin (0.04%). These results demonstrate that regucalcin activates (Ca(2+)-Mg2+)-ATPase in the liver plasma membranes and that it can stimulate ATP-dependent calcium transport across the plasma membranes.
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PMID:Stimulatory effect of regucalcin on ATP-dependent calcium transport in rat liver plasma membranes. 906 4

The effect of regucalcin, a calcium-binding protein, on ATP-dependent Ca2+ transport in the basolateral membranes isolated from rat kidney cortex was investigated. The prepared membranes were in inside-out oriented and membrane vesicles. Ca(2+)-ATPase activity in the basolateral membranes was progressively elevated by increasing concentrations of regucalcin (10(-8) to 10(-6) M) in the reaction mixture. This increase was dependent on Ca2+ addition. The activatory effect of regucalcin on the enzyme is inhibited by the presence of digitonin (5 x 10(-3)%) which can solubilize the membranous lipids. Moreover, the regucalcin effect was clearly abolished by the presence of vanadate (0.1 mM) or N-ethylmaleimide (5.0 mM). However, the effect of calmodulin (6 x 10(-7) M) to increase Ca(2+)-ATPase activity was not significantly inhibited by vanadate or N-ethylmaleimide, indicating that the action mode of regucalcin differs from that of calmodulin. Also, the activatory effect of regucalcin on Ca(2+)-ATPase was appreciably inhibited by addition of dibutyryl cAMP (10(-5) and 10(-3) M), while inositol 1,4,5-trisphosphate (10(-7) and 10(-5) M) had no effect. Dibutyryl cAMP itself did not have an effect on the enzyme activity. Furthermore, the 45Ca2+ uptake by the basolateral membranes was clearly increased by the presence of regucalcin (10(-7) and 10(-6) M). This increase was completely blocked by the presence of vanadate (0.1 mM), N-ethylmaleimide (5.0 mM) or dibutyryl cAMP (10(-4) and 10(-3) M) in the reaction mixture. These results clearly demonstrate that regucalcin, which is expressed in rat kidney cortex, can increase Ca(2+)-ATPase activity and Ca2+ uptake in the basolateral membranes. Regucalcin may play a cell physiologic role as an activator in the ATP-dependent Ca2+ pumps in the basolateral membranes from rat kidney cortex.
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PMID:Activatory effect of calcium-binding protein regucalcin on ATP-dependent calcium transport in the basolateral membranes of rat kidney cortex. 908 42


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