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)

To study the mechanism responsible for pancreatic NaHCO3 secretion, the inhibitor NN'-dicyclohexylcarbodiimide (DCCD) was administered to six secretin-infused, anaesthetized pigs. Pancreatic juice was collected from a catheter in the main pancreatic duct. Secretion rate was measured at several arterial pH values in each animal, both before and after DCCD. 15 (14-30) mumol kg-1 body wt DCCD, intra-arterially, reduced pancreatic NaHCO3 secretion from 296 (234-398) to 181 (134-237) mumol min-1 at arterial pH 7.43 (7.42-7.47). Similar fractional reductions of secretion occurred at lower arterial pH. Pancreatic tissue ATP concentration, 1.8 (1.4-2.0) mumol g-1 wet wt, was not changed by DCCD. DCCD, less than or equal to 10(-4) mol l-1, did not change Na,K-ATPase nor carbonic anhydrase activities in separate in vitro assay systems. It is concluded that DCCD reduced pancreatic NaHCO3 secretion by a mechanism not involving ATP depletion nor inhibition of Na,K-ATPase nor carbonic anhydrase activities in pancreatic cells. Because DCCD inhibits proton pumps, DCCD may have reduced NaHCO3 secretion through interfering with a proton pump involved in extruding H+ from HCO-3 secreting cells to interstitial fluid in the pancreas.
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PMID:NN'-dicyclohexylcarbodiimide (DCCD) reduces pancreatic NaHCO3 secretion without changing pancreatic tissue ATP levels. 302 43

To study whether a proton pump is an integral part of the mechanism responsible for secretin-dependent biliary secretion of HCO-3 ions, the proton pump inhibitor N,N'-dicyclohexylcarbodiimide (DCCD) was systemically administered to six anesthetized, secretin-infused pigs. Because biliary HCO-3 secretion varies with arterial pH, secretion rate was measured at several different arterial pH values, before and after DCCD (25 mumol/kg). At arterial pH 7.45, bile flow was 2.1 (1.6-2.9) ml/min, and HCO-3 secretion was 224 (157-311) mumol/min. DCCD reduced bile flow and HCO-3 secretion by 30% and 40%, respectively, independent of arterial pH. In contrast, bile acid secretion, 46 (41-59) mumol/min, was not changed by DCCD. The hepatic adenosine triphosphatase (ATP) level, 2.0 (1.8-2.1) mumol/g wet tissue, was not changed by DCCD. DCCD (10(-4) mol/l) affected neither Na,K-ATPase nor carbonic anhydrase activities in separate in vitro assay systems. The reduction in biliary HCO-3 secretion induced by the proton pump inhibitor DCCD may indicate that a proton pump is integrated into the mechanism responsible for secretin-dependent biliary secretion of HCO-3.
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PMID:DCCD (N,N'-dicyclohexylcarbodiimide) inhibits biliary secretion of HCO-3. 303 16

We present evidence that cysteine 269 of the small subunit of Escherichia coli carbamyl phosphate synthetase is essential for the hydrolysis of glutamine. When cysteine 269 is replaced with glycine or with serine by site-directed mutagenesis of the carA gene, the resulting enzymes are unable to catalyze carbamyl phosphate synthesis with glutamine as nitrogen donor. Even though the glycine 269, and particularly the serine 269 enzyme bind significant amounts of glutamine, neither glycine 269 nor serine 269 can hydrolyze glutamine. The mutations at cysteine 269 do not affect carbamyl phosphate synthesis with NH3 as substrate. The NH3-dependent activity of the mutant enzymes was equal to that of wild-type. Measurements of Km indicate that the enzyme uses unionized NH3 rather than ammonium ion as substrate. The apparent Km for NH3 of the wild-type enzyme is calculated to be about 5 mM, independent of pH. The substitution of cysteine 269 with glycine or with serine results in a decrease of the apparent Km value for NH3 from 5 mM with the wild-type to 3.9 mM with the glycine, and 2.9 mM with the serine enzyme. Neither the glycine nor the serine mutation at position 269 affects the ability of the enzyme to catalyze ATP synthesis from ADP and carbamyl phosphate. Allosteric properties of the large subunit are also unaffected. However, substitution of cysteine 269 with glycine or with serine causes an 8- and 18-fold stimulation of HCO-3 -dependent ATPase activity, respectively. The increase in ATPase activity and the decrease in apparent Km for NH3 provide additional evidence for an interaction of the glutamine binding domain of the small subunit with one of the two known ATP sites of the large subunit.
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PMID:Catalytic domains of carbamyl phosphate synthetase. Glutamine-hydrolyzing site of Escherichia coli carbamyl phosphate synthetase. 352 65

Transport systems involved in proximal tubule HCO-3 reabsorption were examined in disaggregated renal cortical tubules from rabbits with metabolic alkalosis. The acid-base disorder was induced by first treating the animals with furosemide, and then maintaining them on low Cl--high HCO-3 diets. On this regimen, the rabbits had increases in blood pH and total CO2 values and decreases in serum K+ concentrations. Urine Cl- concentrations were less than 15 mEq/L in all cases. Na+-H+ exchange was evaluated by incubating tubules in rotenone in an Na+-free medium to deplete them of Na+ and adenosine triphosphate. Then the tubules were resuspended in media containing 65 or 12.5 mEq/L Na+ at either pH 7.1 or pH 7.6. The rise in cell pH estimated by dimethadione distribution was taken as a measure of Na+-H+ exchanger activity. At the high incubation pH, Na+-H+ exchanger activity appeared to be the same in tubules taken from alkalotic rabbits compared with those prepared from normal rabbits. At the low incubation pH, the activity of this transport system appeared to be depressed by 40% to 50% in alkalosis, with kinetics that suggested a decreased Vmax for the exchanger. Na+-independent H+ transport, presumably reflecting activity of an H+-adenosine triphosphatase, was evaluated by preincubating tubules in a Na+-free medium in the presence of ouabain, and then sequentially exposing them to and removing them from a solution containing 20 mmol/L NH4Cl.(ABSTRACT TRUNCATED AT 250 WORDS)
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PMID:Proximal tubule hydrogen ion transport processes in diuretic-induced metabolic alkalosis. 400 20

A model for endothelial transport is updated to include recent evidence. We discuss electrolyte movements based on a Na+-K+ ATPase, a Na+-H+ exchanger, a Na+-HCO3 coupler, a Cl- -HCO-3 exchanger, a K+-Cl-coupler, and K+ and anion channels. We discuss near-isotonic transport of fluid on the basis of recent findings of high endothelial osmotic permeability.
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PMID:The mechanism of fluid and electrolyte transport across corneal endothelium: critical revision and update of a model. 401 30

To examine the possible contribution of active H+ secretion mediated by brush border enzymes to proximal tubule HCO-3 absorption, paired reperfusions of surface proximal convoluted tubules were performed with the inhibitor dicyclohexylcarbodiimide (DCCD). In control studies using a solution devoid of HCO-3 but containing 5.5 mM glucose, 1 mM DCCD had no effect on glucose or fluid (Na+) absorption, suggesting that this inhibitor did not interfere with sodium entry at the brush border or mitochondrial energy production (ATP synthesis). In experiments using a perfusion solution containing 18-25 mM HCO-3, DCCD caused a fall in absolute CO2 absorption of approximately 15% under eucapneic conditions and 30% during acute hypercapnia. One millimole per liter amiloride (an inhibitor of the passive Na+-H+ exchanger) caused a 15% inhibition of CO2 absorption during acute hypercapnia and a disproportionately large reduction in fluid (Na+) absorption. The latter was not due to cell poisoning, since 1 mM amiloride had no inhibitory effect on fluid or glucose absorption when a HCO-3-free perfusion solution was used. Addition of 1 mM DCCD to a perfusion solution containing either 10(-3) M amiloride or 10(-4) M acetazolamide caused a significant inhibition of CO2 absorption compared with amiloride or acetazolamide alone. The observations are consistent with the view that in addition to passive Na+-H+ exchange, active transport mediated by either a H+-ATPase or a redox-driven H+ pump in the brush border contributes significantly to HCO-3 absorption in the proximal tubule.
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PMID:Evidence for a DCCD-sensitive component of proximal bicarbonate reabsorption. 406 52

Current ideas about the parietal cell are presented in the model shown in Figure 6; the cell is illustrated both in resting and stimulated states. The basal-lateral surface contains three major receptor classes mediated by either cyclic AMP responses or Ca2+ changes, Ca2+ channels and a Ca2+ pump, and a variety of ion transport pathways such as Na+:H+ and Cl-:HCO-3 exchange, a K+ conductance, a postulated NaKCl2 cotransport and the (Na+ + K+)ATPase. At rest, the tubulovesicles contain the (H+ + K+)ATPase. In the stimulated state, the apical (secretory canalicular) membrane contains a K+ and Cl- conductance as well as the (H+ + K+)ATPase. There is also a change in cytoskeletal arrangement associated with stimulation.
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PMID:Cellular mechanisms of acid secretion. 608 85

1. The effect of the diuretic drug furosemide was studied in detail on ouabain-insensitive, SCN- and OCN- -sensitive C1-/HCO-3-ATPase in homogenates from larval dragonfly rectum (Aeshna cyanea), frog (Rana temporaria) and mouse (Mus musculus) kidney. 2. The in vitro inhibition by the drug studied on the HCO-3-activated enzyme is non-competitive with an inhibitor constant of Ki=4.3 mM furosemide in the case of insect rectum and Ki=0.9 mM furosemide in the case of frog and mouse kidney. 3. Furosemide even at 10 mM concentration which completely inhibits the anion-dependent ATPase has only a little inhibitory effect on the Na+/K+-ATPase of the 3 tissues. 4. The data suggest that furosemide may affect an active chloride transport system involving a C1-/HCO-3-ATPase.
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PMID:The loop diuretic furosemide as non-competitive inhibitor of C1-/HCO3-ATPases of vertebrate kidneys and insect rectum. 612 70

The effects of thyrotrophin, hypophysectomy, and chronic treatment with thyroxine and methimazole on radioiodide uptake (thyroid/plasma (T/P) 125I-ratio), protein and DNA contents and activities of Na+, K+-ATPase, HCO-3 ATPase, and carbonic anhydrase (CA) of rat thyroid gland were evaluated. Thyrotrophin given to intact rats slightly increased thyroid iodide uptake, did not affect protein or DNA content, and slightly inhibited CA activity (units/g cell water). Hypophysectomy markedly decreased T/P 125I-ratio, increased protein content, decreased activity of Na+, K+ -ATPase, and slightly increased HCO-3 -ATPase(nmol/mg DNA per min) and CA (units/g cell water) activities. Thyrotrophin given to hypophysectomized rats (as compared with untreated hypophysectomized control animals) markedly increased T/P 125I-ratio, slightly decreased protein content and decreased Na+, K+-ATPase and CA activities. Chronic treatment with methimazole increased T/P 125I-ratio, decreased protein content, markedly increased NA+, K+-ATPase and HCO-3-ATPase activities, and decreased CA activity. Chronic treatment with thyroxine, in contrast, decreased T/P 125I-ratio, decreased Na+, K+-ATPase activity, and increased CA activity. There was a significant inverse correlation between T/P 125I-ratio and CA activity in follicular cells for the various induced functional states of the thyroid.
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PMID:Correlation of iodide transport with Na + ,K+ ATPase, HCO3-ATPase and carbonic anhydrase activities in different functional states of the rat thyroid gland. 612 35

The authors studied the effect of high-fat and high-protein diets on the activity of some enzymes of rat gastric mucosa parietal cells. It was found that the high-protein diet (40% of protein in terms of caloricity) causes an increase in the activity of both the mitochondrial enzymes of Mg2+-ATPase and HCO-3-ATPase and enzymes of the plasma membrane (K+-ATPase and cytoplasm (carboanhydrase). The high-fat diet (60%) of fat in terms of caloricity) produces different effects on the above-indicated enzymes: the activity of Mg2+-ATPase decreases, while that of HCO-3-ATPase rises; at the same time the activity of K+-ATPase and carboanhydrase diminishes. It was shown that the enzymatic systems responsible for hydrochloric acid secretion in the stomach show a delicate response to a qualitatively different nutrition.
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PMID:[Effect of high-fat and high-protein diets on the enzyme activity participating in hydrochloric acid secretion]. 612 5


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