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

---

Query: EC:3.6.1.3 (ATPase)
65,361 document(s) hit in 31,850,051 MEDLINE articles (0.00 seconds)

Several studies have established that intestinal glutamine (GLN) metabolism is altered during catabolic states. It remains unclear whether these alterations are due to a defect in metabolism or in transport of the amino acid. The present study examines the kinetics of GLN transport across basolateral membrane vesicles (BLMV) of enterocytes obtained from control rats and rats subjected to 20% full-thickness scald burn, 48 hr previously. BLMV were prepared from freshly isolated enterocytes using differential centrifugation with separation on a Percoll density gradient. BLMV were enriched (10- to 12-fold) with Na+-K+-ATPase while markers for brush border membranes were impoverished. Previous studies from our laboratory indicated that, in this preparation, GLN transport is into an osmotically sensitive space, dependent on GLN concentration, linear up to 30 sec, and both temperature and Na+ dependent. Our results indicate that in thermal injury, initial rates of GLN uptake were depressed (y = 3.67 + 0.435X for burned rats vs y = 18.7 + 0.907X for controls, P less than 0.01). Kinetic analysis of GLN uptake showed a marked decrease in transport Vmax (81.8 +/- 15 nmole/mg protein/15 sec for burned rats vs 185 +/- 17 nmole/mg protein/15 sec for controls, P less than 0.001). Transport Km also decreased from 0.25 +/- 0.004 mM for controls to 0.08 +/- 0.03 mM glutamine for burned rats (P less than 0.001). Kinetic studies performed at GLN levels greater than 0.6 mM showed that GLN uptake proceeded by a nonsaturable process in both the control and burned rats. No significant alteration in this nonsaturable component was observed.(ABSTRACT TRUNCATED AT 250 WORDS)
...
PMID:Burn injury alters intestinal glutamine transport. 270 26

The reabsorption of amino acids by the proximal tubule is remarkably efficient. Current evidence indicates that this process occurs by Na+-amino acid cotransport or symport. The energy for amino acid entry is derived from the chemical and voltage gradient for Na+ entry across the apical surface of the renal cell maintained by pumping Na+ out of the cell by Na+-K+-adenosine triphosphatase (ATPase) activity at the basolateral membrane. We chose the beta-amino acid taurine to study the anionic requirements as well as voltage- and pH-dependence of Na+-taurine symport into rat proximal tubule brush border membrane vesicles. Maximal uptake was found when Cl- or Br- were the anions. The addition of various ionophores (amiloride, carbonyl cyanide-n chlorophenyl-hydrazone, and valinomycin) under pH-equilibrated conditions did not change taurine entry into the vesicle. Hill equation analysis of the initial rate of taurine uptake into vesicles indicates that transport operates by means of a 2 Na+:1 Cl-:1 taurine-carrier complex. Because taurine is a zwitterion, this complex has a net positive charge. Its entry into the vesicle is favored by the imposition of an outwardly directed K+ gradient in the presence of valinomycin. The movement of a quaternary complex of this type across the apical surface of the proximal tubular cell would assure that the movement of both Cl- and the amino acid is energized by the Na+ gradient. Because most amino acids are zwitterions at physiologic pH this complex would be positively charged, favoring entry into the voltage negative renal cell interior.
...
PMID:Ionic requirements for amino acid transport. 280 2

1,25-Dihydroxyvitamin D3 (calcitriol), or vitamin D3 itself, when added to cultures of 20-day-old embryonic chick small intestine, stimulated sodium (Na+) uptake from the mucosal surface. The calcitriol-mediated increase in Na+ uptake appeared to be related to increased tight-junctional or paracellular permeability. Support for this conclusion was, first, that the uptake of other ions, potassium (K+) and rubidium (Rb+), with tight-junctional permeabilities greater than Na+, was also stimulated by calcitriol, and second, perturbation of cellular Na+ and K+ fluxes by inhibition of Na+/K+-ATPase activity did not affect calcitriol-stimulated Na+, K+, or Rb+ transport. Calcitriol stimulation of Na+ fluxes across the brush border as an alternate possibility is unlikely for the following reason: the calcium ionophore A23187, while mimicking the stimulatory action of calcitriol on calcium (Ca2+) uptake, reduced epithelial Na+ uptake. It is therefore suggested that calcitriol, by virtue of its effect on Ca2+ transport, reduces rather than stimulates cellular Na+ uptake.
...
PMID:Calcitriol-dependent, paracellular sodium transport in the embryonic chick intestine. 282 8

Mineralocorticoid activity of glycyrrhetinic acid (GR) was studied in vivo (electrical potential difference in rat rectum) and in vitro (brush border Mg2+-HCO3- ATPase in rat small intestine, kidney cytosol binding of GR with and without RU-28362, anti-glucocorticoid compound) in order to clarify the mechanism of mineralocorticoid-like activity of GR. Scatchard analysis of [3H]aldosterone showed that Kd of higher affinity site (type I) 6.0 X 10(-9) M, Bmax 1.0 X 10(-14) mol/mg protein, and Kd of lower affinity site (type II) 1.6 X 10(-7) M, Bmax 7.5 X 10(-14) mol/mg protein. GR competed for [3H]aldosterone binding sites in kidney cytosol at the concentration of 10(4) times as that of unlabeled aldosterone. RU-28362 displaced aldosterone binding curve, whereas GR binding kinetic was not affected by this compound. Adrenalectomy caused a significant fall in brush border Mg2+-HCO3- ATPase activity (75% reduction compared with the initial level) which was not restored by GR administration. Electrical potential differences in the adrenalecomized rats were significantly lower than those in the control rats, which did not increase after GR administration.
...
PMID:Glycyrrhizic acid and its hydrolysate as mineralocorticoid agonist. 282 10

We studied the effects of increased circulating levels of bile salts on jejunal mucosal function in dogs. In situ luminal perfusion of a 30-cm proximal jejunal segment was performed while deoxycholate, cholate, taurodeoxycholate, or taurocholate solutions were directly added to the mesenteric arterial supply, reaching the intestinal wall at successive concentrations of 5, 8, 12, and 22 mumol/L. The transport rates of water, sodium, glucose, fructose, glycine, and lysine were measured. The mucosa of the experimental loop was assayed for ATPase activity, and examined by light and electron microscopy. Deoxycholate at 8 microM in the blood supply of the perfused jejunal segment was associated with a significant (p less than 0.02) reduction in the absorption rates of water, sodium, glucose, and glycine, and inhibition of mucosal Na+, K+-ATPase. The absorption of fructose and lysine, and brush border enzyme activities, were not affected. Cholate had a similar effect at 12 microM. There were no obvious histological alterations, but electron microscopy showed swelling of mitochondria in the enterocytes. The reduction in mucosal transport, the inhibition of mucosal Na+, K+-ATPase, and the mitochondrial swelling were reversed after discontinuation of the bile salt infusion. The taurine conjugates at 22 microM depressed transport of water and sodium only, and did not inhibit Na+, K+-ATPase. Our study indicates that increased circulating concentrations of unconjugated bile salts, particularly deoxycholate, may impair Na+, K+-ATPase-related jejunal mucosal function.
...
PMID:Effect of infusion of bile salts into the mesenteric artery in situ on jejunal mucosal transport function in dogs. 284 Apr 88

The effects of several phenothiazine derivatives (PTDs) and quinidine (QD) on the jejunal microclimate-pH in rats were studied using a microelectrode. Chlorpromazine, thioridazine, chlorpromazine sulfoxide (CPZSO), trifluoperazine, prochlorperazine, and QD at concentrations of 1 mM increased this microclimate-pH by 0.15-0.3 pH units, while 1 mM diethazine and 1 mM promethazine had little effect on it. The increases in the microclimate-pH caused by PTDs and QD were concentration dependent and reversible. We studied the effects of PTDs on the fluidity of intestinal brush border membranes and on the release of proteins from the intestinal tissue to the lumen. The PTD-induced changes in microclimate-pH could not be explained by either of these nonspecific effects on the membranes. Then, the effects of PTDs on Na+,K+-ATPase activity and Mg2+-ATPase activity were studied using the jejunal homogenate. Each PTD inhibited Na+,K+-ATPase and Mg2+-ATPase activity to some extent. The inhibitory effects on Na+,K+-ATPase and Mg2+-ATPase activity were compared with the PTD-induced increases in the microclimate-pH. No good correlation was obtained between the IC50 values of PTDs for Na+,K+-ATPase activity and the concentrations required to increase the microclimate-pH by 0.1 pH unit, while IC50 values of PTDs for Mg2+-ATPase activity showed a relatively good correlation, except for that of CPZSO. These findings suggest that the effects of PTDs on the microclimate-pH were not nonspecific, although the increases in the microclimate-pH caused by PTDs cannot be fully explained by the inhibitory effects of these compounds on either Na+,K+-ATPase activity or Mg2+-ATPase activity alone.
...
PMID:Effects of phenothiazine derivatives on the microclimate-pH in the rat jejunum. 284 51

Rats received 0.1% lead acetate in their drinking water for 3 weeks or for 6 weeks, at which time renal brush border fractions were obtained for measurement of enzyme activity. Renal brush border preparations from Pb2+-exposed rats exhibited statistically significant decreases in the activity of gamma-glutamyl transpeptidase and alanine aminopeptidase after 3 or 6 weeks of treatment. There was an increase in the activity of alkaline phosphatase which was statistically significant after 3 weeks of Pb2+ exposure. The (Na+,K+) adenosine triphosphatase activity and urokinase activity, located in the basolateral membrane fractions, were unchanged by Pb2+ exposure, as were the protein and phospholipid contents of the brush border fractions. The results are compared to those following acute exposure to Pb2+ or Cd2+.
...
PMID:Rat kidney brush border enzyme activity following subchronic oral lead exposure. 285 32

We have used two actin-binding proteins of the intestinal brush border, TW 260/240 and villin, to examine the effects of filament cross-linking and filament length on myosin-actin interactions. TW 260/240 is a nonerythroid spectrin that is a potent cross-linker of actin filaments. In the presence of this cross-linker we observed a concentration-dependent enhancement of skeletal muscle actomyosin ATPase activity (150-560% of control; maximum enhancement at a 1:70-80 TW 260/240:actin molar ratio). TW 260/240 did not cause a similar enhancement of either acto-heavy meromyosin (HMM) ATPase or acto-myosin subfragment-one (S1) ATPase. Villin, a Ca2+-dependent filament capping and severing protein of the intestinal microvillus, was used to generate populations of actin filaments of various lengths from less than 20 nm to 2.0 microns; (villin:actin ratios of 1:2 to 1:4,000). The effect of filament length on actomyosin ATPase was biphasic. At villin:actin molar ratios of 1:2-25 actin-activated myosin ATPase activity was inhibited to 20-80% of control values, with maximum inhibition observed at the highest villin:actin ratio. The ATPase activities of acto-HMM and acto-S1 were also inhibited at these short filament lengths. At intermediate filament lengths generated at villin:actin ratios of 1:40-400 (average lengths 0.26-1.1 micron) an enhancement of actomyosin ATPase was observed (130-260% of controls), with a maximum enhancement at average filament lengths of 0.5 micron. The levels of actomyosin ATPase fell off to control values at low concentrations of villin where filament length distributions were almost those of controls. Unlike intact myosin, the actin-activated ATPase of neither HMM nor S1 showed an enhancement at these intermediate actin filament lengths.
...
PMID:Effects of actin filament cross-linking and filament length on actin-myosin interaction. 293 51

ATPase activity which is stimulated by submicromolar concentrations of calcium (Ca2+) was identified in human placental microvillous brush border membranes. The high-affinity enzyme has an apparent K0.5 for free Ca2+ of 18.3 +/- 3.7 nM and a Vmax of 233.0 +/- 30.0 nmol/min/mg protein. Studies using trans-1,2-diaminocyclohexane-N,N,N1,N1-tetraacetic acid (CDTA) show that this enzyme requires submicromolar concentrations of Mg2+ for maximal activity, but that it appears to have a low basal activity in the absence of this cation. The high-affinity Ca2+-ATPase was unaffected by up to 100 microM concentrations of vanadate, but was sensitive to trifluoperazine inhibition (I50 less than 50 microM). It was not found to be stimulated by the addition of up to 10 micrograms calmodulin, but this lack of effect may be related to the endogenous calmodulin content of the membrane preparation. A low-affinity, non-specific divalent cation ATPase was also identified in this membrane preparation. In contrast to the high-affinity enzyme, it has an apparent K0.5 for calcium of 99.7 +/- 22.1 microM, and a Vmax of 1.54 +/- 0.17 mumol/min/mg protein. The characteristics of the high-affinity Ca2-ATPase are similar to those of other Ca2+- ATPases known to transport and regulate intracellular calcium concentrations in other tissues. By analogy, we suggest that the high-affinity Ca2+-ATPase described here could play an important role in cellular calcium homeostasis in the human placenta.
...
PMID:High-affinity, calcium-stimulated ATPase in brush border membranes of the human term placenta. 294 89

Bicarbonate-stimulated Mg2+ dependent ATPase activity was demonstrated both biochemically and cytochemically, in brush border membranes from rat, rabbit and guinea pig duodenum. There was no correlation between enzyme activity and basal HCO3- secretion rates in the different species. The concentration of HCO3- necessary for optimal stimulation of ATPase activity, degree of stimulation and total activity was higher in the rat than in other species. Activity was higher in rat duodenum than in the ileum. This is consistent with the proposed electrogenic HCO3- secretion in the duodenum. Distribution of activities of alkaline phosphatase and HCO3(-)-stimulated Mg2+-ATPase along the duodenal villus showed significant differences, suggesting that the two activities reflect, at least in part, distinct enzymes.
...
PMID:Biochemical and cytochemical comparison of intestinal bicarbonate-stimulated Mg2+ dependent ATPase and alkaline phosphatase activities in rat, rabbit and guinea pig. 295 98


<< Previous 1 2 3 4 5 6 7 8 9 10 Next >>

---