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)

Ion-replacement studies were carried out in the isolated perfused rat liver to obtain insight into the role played by inorganic electrolytes in bile acid-independent canalicular bile flow (BAICF). The BAICF decreased significantly when Na+ (146 mM) was replaced by 120 mM K+, Rb+, Cs+, or choline and when Cl- (127 mM) was replaced by 120 mM acetate or isethionate; there was no reduction in BAICF when Na+ was replaced by Li+ (146 mM) and Cl- by NO-3. K+, Rb+, and Cs+, however, also caused a simultaneous decline in the perfusion rate. The BAICF decreased by 50% when HCO-3 was replaced by equimolar tricine; under this condition replacement of Cl- by NO-3, but not Na+ by Li+, decreased BAICF by 45%. Thus the hepatic transport of Cl- cannot be explained by simple diffusion only, and a special mechanism, probably Na+-coupled Cl- transport, may contribute about 30% of the BAICF. With Li+ replacing Na+ in the medium, the intracellular concentration of Li+ in isolated rat hepatocytes was less than that calculated for electrochemical equilibrium and was increased by 2 mM KCN, indicating active extrusion of this ion. Li+ was unable to activate Mg2+-ATPase of isolated rat liver plasma membranes, and 1 mM ouabain did not affect the Li+ distribution. These results suggest the potential importance of ion pumps other than Na+-K+-ATPase in BAICF.
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PMID:Role of inorganic electrolytes in bile acid-independent canalicular bile formation. 613 Jul 5

Mg2+-dependent and HCO-3-stimulated ATPase activity was highest in the brush border (microvilli) of rat duodenal mucosa compared with that of the other gastrointestinal mucosa. This ATPase may be useful to neutralize the gastric acid in the duodenal lumen. Carbonic anhydrase seems to accomplish a subsidiary role in the above reaction.
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PMID:Mg2+-HCO-3-ATPase and carbonic anhydrase in rat intestinal mucosa. 613 24

The possible role of Mg2+-HCO3-ATPase, carbonic anhydrase and several other enzymes in rat intestinal mucosa as mediators of the action of aldosterone has been examined. The small-intestinal tract was cut into seven segments, 15 cm each in length and the mucosa was scraped off, homogenized in 50 mM D-mannitol-2 mM Tris-HCl buffer (pH 7.1), differentially fractionated and a crude brush border was obtained. The mucosa from the colon and rectum was combined and used as the large-intestinal sample. Five days after the adrenalectomy, activities of brush border Mg2+-HCO3-ATPase and supernatant carbonic anhydrase from the upper small intestine decreased to about 60 and 40% of normal values, respectively. Activities of Na+-K+-ATPase, beta-glycerophosphatase and succinate dehydrogenase were all decreased. Two and 4 h after i.p. injection of aldosterone (40 micrograms/kg) to adrenalectomized rats, all enzyme activities increased except for Na+-K+-ATPase in the upper small intestine. In contrast, Mg2+-HCO-3-ATPase and carbonic anhydrase activities were unchanged 3 h after i.p. injection of dexamethasone (200 micrograms and 1 mg/kg). The activation of both Mg2+-HCO3-ATPase and carbonic anhydrase by a single injection of aldosterone was blocked by pretreatment with cycloheximide (1 mg/kg). These results suggest that aldosterone may induce the synthesis of enzyme proteins in the intestinal mucosa.
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PMID:Brush border Mg2+-HCO-3-ATPase, supernatant carbonic anhydrase and other enzyme activities isolated from rat intestinal mucosa: effect of adrenalectomy and aldosterone administration. 613 8

Cytochemical techniques were used to demonstrate, with appropriate controls, alkaline phosphatase and HCO-3-activated adenosine triphosphatase (ATPase) in rat duodenal brush border microvillus membranes. Intense activity of ecto-alkaline phosphatase activity was demonstrated with 2-glycerophosphate as substrate. Although biochemical assays suggested that L-phenylalanine inhibited both alkaline phosphatase and HCO-3-activated ATPase, cytochemical studies indicated that there was marked inhibition of alkaline phosphatase revealing a specific HCO-3-activated ATPase on the inner aspect of the microvillus membrane. While it is tempting to suggest that this HCO-3-activated ATPase is implicated in active bicarbonate secretion by the duodenum, decisive identification is not yet possible.
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PMID:Cytochemical studies on the localization of alkaline phosphatase and HCO-3-activated adenosine triphosphatase in the brush border membrane of rat duodenal enterocytes. 614 Feb 47

Activity of a HCO-3 stimulated Mg2+ dependent ATPase is demonstrated in mitochondrial fractions of the avian duodenum. Suppression of eggshell calcification resulted in a slight reduction in Mg2+, Ca2+ and Mg2+HCO-3 ATPase activities. Duodenal carbonic anhydrase activity was lower in birds laying soft-shelled eggs than in birds laying normal eggs. Alkaline phosphatase and calcium binding protein levels both decreased along the length of the small intestine, but the effect was more pronounced for alkaline phosphatase. Suppression of eggshell calcification and treatment of shell-less laying hens with 1,25(OH)2D3 influenced alkaline phosphatase activity only in the duodenal mucosa. Suppression of eggshell calcification reduced CaBP levels in all sections of the intestine. Treatment with 1,25(OH)2D3 restored CaBP levels. Regulation of intestinal CaBP levels by 1,25(OH)2D3 would therefore, seem to be controlled more directly by calcium requirements associated with eggshell calcification than by gonadal hormones.
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PMID:Effects of suppression of eggshell calcification and of 1,25(OH)2D3 on Mg2+, Ca2+ and Mg2+HCO-3 ATPase, alkaline phosphatase, carbonic anhydrase and CaBP levels--II. The laying hen intestine. 614 59

Mucosal homogenates from rat jejunum were tested for both HCO-3-stimulated ATPase and anion-stimulated, SCN-inhibited ATPase in assay mixtures ungassed, gassed with pure oxygen or gassed with the appropriate gaseous phase. Experiments were performed at four different initial pHs (7.15; 7.45; 8.10; 8.55) with or without the presence of Triton X-100. Assay mixtures were tested for both pH and % CO2. Only at pH 7.15 and 7.45 anion-sensitive ATPase activities in ungassed conditions are different from those in mixtures gassed with the proper gaseous phase. Moreover, at cited pHs in ungassed mixtures the final pH is higher and % CO2 is lower than initial values. Therefore it seems possible to obtain the exact determination of anion-sensitive ATPases at all pH values only from mixtures gassed with the proper gaseous phase. Bicarbonate-stimulated ATPase activity is absent both at pH 7.15 and 7.45; this fact seems to exclude, at these pHs, an active transport of bicarbonate directly depending on this enzyme activity.
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PMID:ph-dependent, HCO-3-stimulated ATPase of rat jejunum. 618 53

The outward-facing (OFM) and inward-facing (IFM) membranes of the surface epithelial syncytium of Schistosoma mansoni were separated by sequential exposure to saponin solutions. The OFM, containing both inner and outer bilayers, contained ATPase activity that was stimulated by Mg2+ and Ma+, but not K+ or HCO-3, and was inhibited by Ca2+ and ethacrynic acid. The OFM enzyme was unaffected by ouabain, oligomycin, SCN- and azide and had a pH optimum of 7.5. The OFM ATPase therefore has properties similar to ATPases characterized from the apical membrane of a variety of epithelial cells where it is thought to augment the regulatory cell volume decreasing function of (Na++K+)Mg2+- ATPase. The IFM contained ATPase activity that was stimulated by Mg2+, Na+ and K+, and was inhibited by ouabain indicating the IFM enzyme was the Na+-pump ATPase. The results are discussed in terms of the transepithelial transport function of the surface epithelial syncytium and a Ca2+-ATPase reported previously from the OFM of S. mansoni.
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PMID:Enrichment and partial enzyme characterization of ATPase activity associated with the outward-facing membrane complex and inward-facing membrane of the surface epithelial syncytium of Schistosoma mansoni. 621 5

Rat liver carbamoyl-phosphate synthetase I is shown to have synthetase and ATPase activity in the absence of acetylglutamate. Km values for ATP, Mg2+ and K+ are greatly increased, the Km for HCO-3 is not changed much, and the Km for NH+4 is markedly reduced. Vmax for the synthetase reaction is less than 20% of that of the acetylglutamate-activated enzyme whereas Vmax for the ATPase activity is greater than 40% of that with acetylglutamate. Pulse-chase experiments with H14CO-3 show formation of less "active CO2" (the central intermediate) than with acetylglutamate; ATPase activity is reduced in proportion, but the synthetase activity is much smaller. Binding of one ATP molecule with high affinity (Kd = 20-30 microM) is shown in the absence of acetylglutamate. This appears to be the molecule of ATPB (ATPB provides the phosphoryl group of carbamoyl phosphate). In contrast, the affinity for ATPA (ATPA yields Pi) is much reduced. Initial velocity measurements without acetylglutamate show a time lag before reaching a constant velocity. At 50 microM acetylglutamate the lag is much longer, but at 10 mM acetylglutamate it is shorter. Activation by acetylglutamate requires ATP at concentrations sufficient to occupy the ATPA and the ATPB binding sites. Preincubation with 10 mM acetylglutamate alone shortens the activation time. From these findings we propose an allosteric model for activation of carbamoyl-phosphate synthetase in which there are two active states, R and R . AcGlu. Binding of ATPA is associated with the conversion of T to R. R . AcGlu differs from R in that transfer to carbamate of the gamma-phosphoryl group of ATPB appears to be facilitated.
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PMID:Mitochondrial carbamoyl phosphate synthetase activity in the absence of N-acetyl-L-glutamate. Mechanism of activation by this cofactor. 622 15

Double-barreled liquid ion-exchanger microelectrodes were used to measure basolateral membrane potential (VBL) and intracellular potassium activity (aiK) in superficial proximal straight tubules (sPST) of the rabbit perfused in vitro. The mean +/- SE (number of cells in parentheses) value of VBL was -37.8 +/- 2.49 (20) vM and aiK was 48.6 +/- 2.27 (20) mM. The calculated Nernst equilibrium potential (EK) across the basolateral membrane was -68 mV. Lowering both potassium concentration to 0.1 mM reversibly decreased both VBL and aiK to -12.2 +/- 1.21 (19) mV and 11.3 +/- 1.29 (19) mM, respectively. Bath ouabain (10(-5) resulted in similar changes. These results demonstrate that intracellular potassium is actively accumulated in sPST perfused in vitro and that accumulation results primarily from Na-K-ATPase activity in the basolateral membrane. During recovery from low K bath, the temporal relationship between VBL and aiK and the effects of ouabain and high K bath on recovery are used to demonstrate directly electrogenic pumping. Lowering bath pH to 6.7 (HCO-3 = 5 mM) and the presence of 0.5 mM BaCl2 in the bath resulted in a large and rapid depolarization of VBL with little or no change in aiK. These results suggest that the response of VBL to both maneuvers is caused by a decrease in potassium permeability of the basolateral membrane.
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PMID:Intracellular potassium activity in the rabbit proximal straight tubule. 627 17

Perfusion of rat jejunal segments in vivo with an isotonic, HCO3-free SO4-Ringer solution resulted in low rates of net sodium (JNanet) and water absorption. When the perfusion fluid was changed to one containing 25 mM Na2SO3, JNanet increased from 4.7 +/- 1.2 to 11.6 +/- 1.5 (SE) mumol X cm-1 X h-1 (P less than 0.001). This increased absorption was accompanied by comparable increases in chloride and water absorption, occurred without a detectable change in potential difference across the perfused segment, and was readily reversed on reinstitution of perfusion with SO4-Ringer. Perfusion with SO3-Ringer had no effect on electrolyte absorption from terminal segments of rat ileum. Addition of L-phenylalanine stimulated absorption from SO4-Ringer perfusate but not from SO3-Ringer perfusate. Addition of 25 mM NaHCO3 to SO4-Ringer perfusate caused parallel increases in JNanet and JHCO3net; when 25 mM NaHCO3 was added to SO4-Ringer perfusate that also contained 25 mM NaSCN, the same increase in JHCO3net occurred but was not associated with any increase in JNanet. These results indicate a potent effect of SO2-3 and HCO-3 to stimulate JNanet from rat jejunum but not from ileum. These anion effects on intestinal transport in vivo resemble their effects on ATPase activity of brush-border fractions from small intestine in vitro and raise the possibility that these effects on ion transport could be mediated through the changes in brush-border ATPase activity, which are brought about by exposure to these anions, although other explanations are also possible.
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PMID:Anion effects on fluid absorption from rat jejunum perfused in vivo. 629 85


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