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)

The basolateral segment of the rat renal tubular plasma membrane possesses Ca2+-dependent ATPase activity which was independent of Mg2+. Two kinetic forms were found: one, was a high affinity (apparent Km for free Ca2+ of 172 nM) low capacity (Vmax of 144 nmol of Pi X min-1 mg-1 protein) type; the other, had low affinity (apparent Km of 25 microM) and high capacity (896 nmol of Pi X min-1 X mg-1 protein). Mg2+ inhibited both Ca2+-ATPases. The high affinity enzyme exhibited positive cooperativity with respect to ATP, with a n value of 1.6. Ca2+-ATPase activity was not affected by calmodulin and was not inhibited by vanadate. On the other hand, both high and low affinity Ca2+-ATPase activities were increased when 1,25-dihydroxycholecalciferol was given to vitamin D-deficient rats. Kinetically, the enhanced activities were due to an increase in the Vmax values; the apparent affinities for free Ca2+ were not changed. The physiological function of the vitamin D-sensitive, Mg+-independent, Ca2+-ATPase activities remains to be established.
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PMID:Ca2+-dependent ATPases in the basolateral membrane of rat kidney cortex. 241 21

The Ca2+ pump in rat duodenal epithelium is studied as ATP-dependent Ca2+ uptake in a vesicle preparation with a 9-fold purification in Na+-K+-ATPase activity and a 20-fold purification of Na+-K+-ATPase with respect to an endoplasmic reticulum marker. ATP-dependent Ca2+ uptake is reduced by 60% by digitonin treatment of the vesicles, whereas high-affinity Ca2+-ATPase is stimulated by the same treatment. Different methods to deplete membrane preparations of calmodulin have been used. In EDTA osmotically shocked vesicles, calmodulin stimulated ATP-dependent Ca2+ transport up to 100% in a Ca2+ concentration-dependent manner. The duodenal Ca2+ pump is inhibited by calmodulin antagonists only at low Ca2+ concentrations and in membranes not depleted from calmodulin. Vitamin D-dependent Ca2+-binding protein (Mr = 10,000) in concentrations up to 5 microM did not affect the rate of ATP-dependent Ca2+ transport, either in Ca2+-EGTA-buffered solutions or in EGTA-free solutions. In membrane preparations from vitamin D-deficient rats, the effects of calmodulin and of Ca2+-binding protein were identical to the vitamin D-repleted control preparations. This excludes a specific effect of Ca2+-binding protein and calmodulin in the vitamin D dependency of duodenal Ca2+-ATPase.
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PMID:Regulation of duodenal Ca2+ pump by calmodulin and vitamin D-dependent Ca2+-binding protein. 242 70

The Ca-pump in rat intestinal basolateral membranes had been studied previously as vesicular ATP-dependent Ca-uptake. In the present studies, Ca-stimulated ATP hydrolysis (Ca-ATPase activity) was measured and found to differ from the Ca-pump in having higher activity and being insensitive to vanadate. Whereas the pump was specific for ATP, hydrolytic activity was found with ATP, GTP or ADP but not with AMP or p-nitro-phenyl-phosphate. In contrast to Ca-pump activity, Ca-ATPase activities were similar for different intestinal segments, for duodenal villus/crypt cell-fractions and for vitamin D-deficient animals. Thus, as usually measured, intestinal basolateral membrane Ca-ATPase activity is not equivalent to the Ca-pump.
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PMID:Intestinal basolateral membrane Ca-ATPase activity with properties distinct from those of the Ca-pump. 243 87

We have previously shown that the human kidney distal convoluted tubule (DCT) contains epitopes of the human erythrocyte Ca++-Mg++ ATPase pump (J Clin Invest 80: 1225-1231, 1987). To determine whether vitamin D-dependent 28-kilodalton-calcium binding protein (28kDa-CaBP)and Ca++-Mg++ ATPase are present in the same cells of the human kidney, kidney tissue was examined for immunoreactivity with antibodies directed against these proteins. Double-label immunohistochemistry showed that a majority of the distal convoluted tubules contain epitopes to both of these proteins. portions of the distal nephron which were positive for 28kDa-CaBP did not show anti-Ca++-Mg++ ATPase antibody binding. All other portions of the nephron were negative for both proteins. Western blot analysis of kidney homogenates by 7% sodium dodecyl sulfate polyacrylamide gel electrophoresis (SDS-PAGE), showed binding of an anti-Ca++-Mg ATPase monoclonal antibody to a major band of Mr = 140,000. Western blots of kidney homogenates by 10% SDS-PAGE also showed binding of an anti-28kDa-CaBP polyclonal antibody to a protein band at Mr = 28,000. Incubation of parallel blots from the same 10% gel with 45CaCl2 demonstrated that the Mr = 28,000 band binds calcium. This work demonstrates, for the first time, that epitopes of vitamin D-inducible 28kDa-CaBp and human erythrocyte Ca++-Mg++ ATPase pump are present in the same cells of the human kidney. Previous work in our laboratory has shown that 28kDa-CaBP binds calcium in a manner analogous to calmodulin, a known regulator of the erythrocyte Ca++-Mg ATPase pump (J Biol Chem, 1987).(ABSTRACT TRUNCATED AT 250 WORDS)
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PMID:Co-localization of erythrocyte Ca++-Mg++ ATPase and vitamin D-dependent 28-kDa-calcium binding protein. 246 Jun 62

In order to further test the validity of the vesicular transport model of 1,25-dihydroxyvitamin D3 (1,25(OH)2D3)-stimulated intestinal calcium absorption, dose-response studies were undertaken. Using previously established methodology for subcellular fractionation following 45Ca absorption from in situ ligated duodenal loops, radionuclide levels were found to increase gradually in endocytic vesicles prepared from 1,25(OH)2D3-treated (+D) chicks relative to controls (-D) achieving a plateau at greater than or equal to 260 pmol seco-steroid. By comparison, lysosomal 45Ca levels increased more readily, having +D/-D ratios of 1.88 +/- 0.35, 2.21 +/- 0.05, 2.17 +/- 0.88, 2.31 +/- 0.25, and 2.15 +/- 0.47 after 0.0104, 0.052, 0.26, 1.3, or 6.5 nmol of 1,25(OH)2D3, respectively. Net intestinal calcium absorption, as judged by appearance of 45Ca in the serum for the same range of doses, rose gradually to a plateau value at greater than or equal to 260 pmol. Since lysosomal 45Ca levels were maximally increased at 1,25(OH)2D3 doses lower than those required for fully stimulated transport, it was concluded that lysosomes are still candidates for cellular calcium carriers, but that other elements of the transport pathway are required. Analyses of gradient fractions for calbindin-D28K (the vitamin D-induced calcium binding protein), and potential 1,25(OH)2D3-mediated changes in vesicular ATPase (microtubule motive power for transcellular delivery of calcium) failed to identify the missing components.
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PMID:1,25-Dihydroxyvitamin D3-mediated vesicular calcium transport in intestine: dose-response studies. 253 14

The intestinal absorption of calcium is certainly a complex process, dependent on several factors of which vitamin D, via 1,25(OH)2D3, is the major controlling hormone. The efficiency of calcium absorption is a function of calcium status and calcium need. As the body's demand for calcium increases, the process commonly termed, adaptation, is activated in which the synthesis of 1,25(OH)2D3 from precursor is increased, resulting in the stimulation of the rate of calcium absorption. The increased demand for calcium might result from the ingestion of a diet deficient in calcium, from growth, pregnancy, lactation and egg shell formation in the laying hen. Accomapanying the change in calcium absorptive efficiency are molecular modifications of the transporting enterocytes, some mentioned herein and elsewhere (Wasserman & Chandler, 1985; Wasserman, 1980; Wasserman et al., 1984). Highly correlated with the rate of calcium absorption under a wide variety of conditions is the concentration of the vitamin D-induced calcium-binding protein, calbindin-D28K (avian type) and calbindin-D9K (mammalian intestinal type). The role of calbindin-D in this transport process is not precisely known but is considered to act at the present time as a cytosolic facilitator of Ca2+ diffusion from the brush border membrane to the basolateral membrane. In addition to the induction of calbindin-D synthesis, 1,25(OH)2D3 exerts other effects on the intestinal epithelium that can have consequences on the calcium absorptive process. Some of these effects are summarized in Figure 14. Vitamin D-dependent reactions might be either direct effects of 1,25(OH)2D3 or indirect effects due to elevated intracellular Ca2+ concentrations. These include changes in the fluidity of the brush border membrane, an increase in microvillar alkaline phosphatase-low affinity Ca-activated ATPase activity, an association of calmodulin with the 105 kD brush border cytoskeletal protein and, following calbindin D synthesis, the binding of calbindin D to a 60 kD brush border protein and to microtubules. The latter has been suggested to be related to the proposed transfer of Ca2+ by an endocytotic-exocytotic mechanism. In addition, a vitamin D-dependent intestinal membrane calcium-binding protein has been identified (Kowarski & Schachter, 1980). Playing into this multi-component system is a stimulation of cyclic nucleotide synthesis by 1,25(OH)2D3 which, through activation of cyclic nucleotide-dependent protein kinases, might modify membrane Ca2+ "channels" by phosphorylation reactions.4+ Intracellular organelles, i.e., the endoplasmic reticulum, mitochondria, the Golgi apparatus, are potent sequesters of Ca2+ and could contribute to the protection of the cell from excessively high Ca2+ concentrations by transiently storing absorbed Ca2+.
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PMID:On the molecular mechanism of intestinal calcium transport. 254 94

In an effort to extend our studies on Ca2+ pumps to animal models, we developed a new monoclonal antibody (5F10) prepared against the human erythrocyte Ca2+-Mg2+-adenosinetriphosphatase (ATPase) that recognizes a protein of approximately 140 kDa in rat kidney homogenates. Enzyme-linked immunosorbent assays show that monoclonal antibody 5F10 binds purified Ca2+-Mg2+-ATPase and rat kidney membrane extracts in a concentration-dependent manner. In paraffin-embedded tissue sections, antibody 5F10 binds to an epitope in the basolateral membranes of rat kidney distal convoluted tubule principal cells. The antibody does not bind to intercalated cells. The latter cells were characterized by the presence of large amounts of carbonic anhydrase C. Polyclonal antibodies directed against chick intestinal 28-kDa vitamin D-dependent calcium binding protein (28-kDa CaBP) also bind epitopes in distal convoluted tubule cells, connecting tubules, and portions of collecting duct but not intercalated cells. Western blot and 45Ca blot analysis of renal cytosolic proteins showed that the polyclonal 28-kDa CaBP-directed antibody detects a protein which also binds calcium. Western blot analysis with monoclonal antibody 5F10 shows binding to both the authentic purified erythrocyte Ca2+ pump (approximately 138 kDa) and to tryptic fragments of this pump. Antibody JA3, previously used for staining of human kidney tubules, reacts with a different set of tryptic fragments, showing that the two antibodies are directed against different regions or conformational determinants on the pump molecule. We show that Ca2+-Mg2+-ATPase and 28-kDa CaBP are present in the principal cells of the distal convoluted tubule of the rat and are absent in intercalated cells.(ABSTRACT TRUNCATED AT 250 WORDS)
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PMID:Plasma membrane calcium pump and 28-kDa calcium binding protein in cells of rat kidney distal tubules. 255 40

Renal calcium transport is described as the result of two processes, a paracellular, gradient-dependent process that predominates in most segments of the nephron and a transcellular, energy-dependent step that characterizes calcium transport in the distal convoluted tubule (DCT). Transcellular calcium transport involves entry into the DCT cell, possibly via channels, intracellular movement which appears to be facilitated by the presence of the vitamin D-dependent, cytosolic calcium-binding protein (CaBPr, calbindin D28k, mol mass approximately 28 kDa), and extrusion via the Ca-ATPase. Although much is known about calcium channels, their presence in renal tissue has only been demonstrated by preliminary studies. Quantitative data on CaBPr content of rat DCT are also unavailable, but theoretical analysis and early experimental values of intracellular self-diffusion of calcium have confirmed the need for an intracellular calcium "ferry," i.e., a molecule like CaBPr to amplify intracellular calcium movement. Available data on the plasma membrane Ca-ATPase are consistent with the extrusion kinetics attributed to the renal Ca-ATPase, but it has not been isolated, nor has its gene been cloned. Regulation and disorders of renal calcium transport are likely to involve one of the three transcellular steps, but indirect regulation by modification of the cell walls and molecules constituting the paracellular pathway cannot be excluded.
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PMID:Renal calcium transport: mechanisms and regulation--an overview. 268 64

A cytochemical technique for the electron microscopic localization of calcium adenosine triphosphatase (Ca-ATPase) was utilized to localize this enzyme in the enterocytes of rachitic and vitamin D-replete chicks. In animals treated with cholecalciferol (CC, vitamin D3), an electron-dense reaction product was located along the basolateral membranes of the absorptive cells within 72 hr after injection. Similarly, a reaction product was identified in association with the basolateral membranes within 24 hr after injection of 1,25-dihydroxycholecalciferol, the active metabolite of vitamin D. A microvillar reaction product was not seen in either of these two groups. Electron-dense reaction products were also seen in association with mitochondria and scattered throughout the cytoplasm of these enterocytes. The Ca-ATPase reaction product was dependent upon the presence of medium calcium and substrate (ATP), was inhibited by vanadate, and was heat labile. In the rachitic animals, a reaction product indicative of Ca-ATPase activity was not seen in association with either the basolateral membranes or the mitochondria. These data appear to indicate that an energy-requiring calcium-activated membrane pump plays a role in the flux of calcium across the enterocytes of the small intestine.
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PMID:Electron microscopic cytochemical localization of a basolateral calcium adenosine triphosphatase in vitamin D replete chick enterocytes. 283 84

This study compares the effects of vitamins 1,25-dihydroxyvitamin D3 [1,25-(OH)2D3] and 24,25-(OH)2D3 on populations of chondrocytes at different developmental stages. Confluent third passage chondrocytes derived from the resting zone and adjacent growth region of rat costochondral cartilage were cultured in Dulbecco's Modified Eagle's Medium containing 10% fetal bovine serum and increasing concentrations of hormone. After determination of cell number, matrix vesicles and plasma membranes were isolated by differential centrifugation. The effects of hormone on alkaline phosphatase, 5'-nucleotidase, ouabain-sensitive Na+/K+-ATPase, and phospholipid composition were dependent on vitamin D metabolite and were cell specific. Growth cartilage chondrocytes responded primarily to 1,25-(OH)2D3, whereas resting zone cells responded primarily to 24,25-(OH)2D3. 1,25-(OH)2D3 inhibited growth cartilage cell number at pharmacological concentrations and had no effect on resting cartilage cell number. In contrast, 24,25-(OH)2D3 appeared to stimulate resting cartilage cell number at physiological concentrations and inhibit these cells at pharmacological doses, but had no effect on growth cartilage chondrocytes. These data were supported by [3H]thymidine incorporation studies. 1,25-(OH)2D3 stimulated alkaline phosphatase, 5'-nucleotidase activity, and Na+/K+-ATPase activity in the matrix vesicles of growth cartilage cells. 1,25-(OH)2D3 also stimulated Na+/K+-ATPase activity in the matrix vesicles and plasma membranes of resting zone cells. Incubation with 24,25-(OH)2D3 stimulated alkaline phosphatase, 5'-nucleotidase, and Na+/K+-ATPase in the matrix vesicles produced by resting zone cells. In addition, 24,25-(OH)2D3 stimulated Na+/K+-ATPase activity in the plasma membranes of resting zone cells as well as in both matrix vesicles and plasma membranes of growth cartilage cells.
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PMID:The effects of vitamin D metabolites on the plasma and matrix vesicle membranes of growth and resting cartilage cells in vitro. 283 76


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