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Query: EC:3.6.3.1 (Mg2+-ATPase)
 1,484 document(s) hit in 31,850,051 MEDLINE articles (0.00 seconds)

A plasma membrane-enriched fraction was prepared from homogenized rat pancreatic islets by a one-step sucrose gradient centrifugation. Using 125I-wheat germ agglutinin as a plasma membrane probe, a fraction was obtained at a sucrose density of about 1.10 that was enriched in 5'-nucleotidase, Mg2+-ATPase and alkaline phosphatase. The fraction contained little, if any, monoamino oxidase activity, insulin or DNA. Hydrolysis of 3-0-methyl-fluoresceinphosphate was stimulated by K+ (10mM) at a pH optimum of pH 8.2. Hydrolysis of ATP-gamma-32P in the presence of MgCl2 was of high specific activity and was optimum at pH 7.0 and 8.2. K+ did not affect ATP-hydrolysis. At pH 8.2, a small fraction of the total Mg2+-ATPase activity was inhibited by ouabain in the presence of Na+ and K+. Since K+-stimulated phosphatase activity does not correlate with Mg2+-ATPase, the two assay systems define separate enzymatic processes.
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PMID:Cation-dependent phosphatase activites in a rat pancreatic islet plasma membrane fraction prepared by one-step gradient centrifugation. 3 53

Spontaneously hypertensive rats (SHR) and two strains of normotensive rats were compared with respect to enzymatic activities and calcium accumulation of plasma membrane and endoplasmic reticulum enriched fractions from their mesenteric arteries. Increased specific activities of alkaline phosphatase, 5'-nucleotidase and Mg2+-ATPase, and increased ATP-dependent calcium accumulation were found in 5- to 6-month-old SHR as compared to both strains fo age-matched normotensive rats. Alkaline phosphatase was increased in 33-day-old "early hypertensive" and 3- to 4-month-old SHR, but 5'-nucleotidase, Mg2+-ATPase, and calcium accumulation were not. Hydralazine treatment of young SHR partially prevented the increase of both alkaline phosphatase activity and blood pressure that develops with age. The relationship between alkaline phosphatase activity and the alterations in vascular reactivity associated with hypertension remains to be determined.
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PMID:Relationship between blood pressure of spontaneously hypertensive rats and alterations in membrane properties of mesenteric arteries. 13 88

To determine whether choleretic infusions of bile acids modified the function or structure of the membrane of the bile canaliculus, sodium taurocholate (NaTc) or dehydrocholate (DHC) was infused into male rats at a rate of 80 mumoles per hour over an 18-hour period. Bile was collected by fistula and phospholipid and cholesterol content was measured in bile, liver homogenates, and isolated liver plasma membranes (LPM) enriched in bile canaliculi. Na+, K+-ATPase, Mg2+-ATPase, 5'-nucleotidase, and alkaline phosphatase activities were also measured in LPM. NaTc infusions enhanced cholesterol and phospholipid output in the bile in association with a significant increase in phospholipid in both LPM and liver homogenate. Although DHC infusions resulted in a comparable excretion of bile acid, phospholipid and cholesterol output in bile did not increase from control values and the concentration of these lipids in LPM and liver homogenate also did not change. However, LPM Na+, K+-ATPase significantly increased after DHC infusions compared to NaTc-infused animals or controls. Neither bile acid altered the activities of Mg2+-ATPase, 5'-nucleotidase, or alkaline phosphatase. Both bile acids increased the diameter of the lumen of the bile canaliculus as assessed by scanning electron microscopy and produced irregularities and outpouchings in the canalicular membrane. Diverticuli and loss of microvilli were most prominent with DHC infusions whereas canalicular side branching and the density of microvilli, either remained unchanged or increased following NaTc infusions. Although the morphologic findings are qualitative, the results of these studies indicate that chronic choleretic infusions of NaTc and DHC have divergent effects, not only on enzyme activities in liver plasma membrane, but on phospholipid composition and 3-dimensional structure. These findings suggest that bile acids may after biliary secretion not only through their osmotic effects, but by modifying lipids and enzymes in the membrane of the bile canaliculus.
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PMID:Effects of chronic choleretic infusions of bile acids on the membrane of the bile canaliculus. A biochemical and morphologic study. 13 67

The intracellular localization of anion-sensitive Mg2+-ATPase in rat pancreas was studied by differential centrifugation, density gradient centrifugation and by the use of inhibitors of mitochondrial Mg2+-ATPase. The anion-sensitive MG2+-ATPase appears to be localized almost exclusively in a mitochondrial (15 min, 15 000 times g) fraction which shows two peaks after density gradient centrifugation. Both peaks coincide with the highest levels of cytochrome c oxidase activity, but not with alkaline phosphatase, (Na+ plus K+)-ATPase and leucine aminopeptidase activities or RNA. They appear to be equal sensitive to inhibition by oligomycin, aurovertin D and the rat liver mitochondrial inhibitor protein, at least when 1 mM EDTA is present in the isolation media. We conclude that no significant plasma membrane-located anion-sensitive Mg2+-ATPase activity is present in rat pancreas.
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PMID:Is there a plasma membrane-located anion-sensitive ATPase? IV. Distribution of the enzyme in rat pancreas. 15 25

Plasma membranes were isolated from rat liver mainly under isotonic conditions. As marker enzymes for the plasma membrane, 5'-nucleotidase and (Na+ + K+)-ATPase were used. The yield of plasma membrane was 0.6-0.9 mg protein per g wet weight of liver. The recovery of 5'-nucleotidase and (Na+ +K+)-ATPase activity was 18 and 48% of the total activity of the whole-liver homogenate, respectively. Judged from the activity of glucose-6-phosphatase and succinate dehydrogenase in the plasma membrane, and from the electron microscopic observation of it, the contamination by microsomes and mitochondria was very low. A further homogenization of the plasma membrane yielded two fractions, the light and heavy fractions, in a discontinuous sucrose gradient centrifugation. The light fraction showed higher specific activities of 5'-nucleotidase, alkaline phosphatase, (Na+ +K+)-ATPase and Mg2+-ATPase, whereas the heavy one showed a higher specific activity of adenylate cyclase. Ligation of the bile duct for 48 h decreased the specific activities of (Na2+ +K+)-ATPase and Mg2+-ATPase in the light fraction, whereas it had no significant influence on the activities of these enzymes in the heavy fraction. The specific activity of alkaline phosphate was elevated in both fractions by the obstruction of the bile flow. Electron microscopy on sections of the plasma membrane subfractions showed that the light fraction consisted of vesicles of various sizes and that the heavy fractions contained membrane sheets and paired membrane strips connected by junctional complexes, as well as vesicles. The origin of these two fractions is discussed and it is suggested that the light fraction was derived from the bile front of the liver cell surface and the heavy one contained the blood front and the lateral surface of it.
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PMID:Subfractionation of rat liver plasma membrane. Uneven distribution of plasma membrane-bound enzymes on the liver cell surface. 17 48

The distribution and properties of cytochemically demonstrable phosphatases in the near-term guinea-pig placenta were examined using a strontium capture technique for sodium- and potassium-dependent adenosine triphosphatase (Na+, K+-ATPase) and a lead capture technique for magnesium-dependent adenosine triphosphatase (Mg2+-ATPase). Localizations with the strontium technique in the presence of an alkaline phosphatase inhibitor were mainly on the syncytiotrophoblast plasma membranes; the reaction was potassium-dependent and ouabain-sensitive. Reaction product using the lead capture method was found on both trophoblast and endothelial cell plasma membranes and was independent of magnesium and insensitive to p-hydroxymercuribenzoate (POHMB), an inhibitor of membrane ATPases. However, a very large proportion of this reaction could be blocked by an alkaline phosphatase inhibitor. It is concluded that the strontium capture technique gave a reliable localization for Na+, K+-ATPase. However, the lead capture method mainly demonstrated alkaline phosphatase, and does not offer a useful approach to specific ATPase studies in this particular system.
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PMID:The localization and properties of membrane adenosine triphosphatases in the guinea-pig placenta. 22 15

The aim of this study was to provide further evidence for the existence of a nonmitochondrial becarbonate-stimulated Mg2+-ATPase in brush border membranes derived from rat kidney cortex. A plasma membrane fraction rich in brush border microvilli and a mitochondrial fraction were isolated by differential centrifugation. Both fractions contain a Mg2+-ATPase activity which can be stimulated by bicarbonate. The two Mg2+-ATPases are stimulated likewise by chloride, bicarbonate, and sulfite or inhibited by oligomycin and aurovertin, though to different degrees. In contrast to these similarities, only the Mg2+-ATPase activity of the mitochondrial fraction is inhibited by atractyloside, a substance which blocks an adenine nucleotide translocator in the inner mitochondrial membrane. On the other hand, filipin, an antibiotic that complexes with cholesterol in the membranes inhibits exclusively the Mg2+-ATPase of the cholesterol-rich brush border membranes. Furthermore it could be demonstrated by the use of bromotetramisole, an inhibitor of alkaline phosphatase activity, that the Mg2+-ATPase activity in the membrane fraction is not due to the presence of the highly active alkaline phosphatase in these membranes. These results support the assumption that an intrinsic bicarbonate-stimulated Mg2+-ATPase is present in rat kidney brush border membranes.
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PMID:Further evidence for the existence of an intrinsic bicarbonate-stimulated Mg2+-ATPase in brush border membranes isolated from rat kidney cortex. 22 12

Several analogs of lysolecithin were found to solubilize human erythrocyte ghosts comparably or even better than other detergents. Derivatives with aliphatic chains of 12 to 14 carbons were most effective. The phosphorylcholine detergents apparently possess low protein-denaturing properties, since they, for the first time, allowed the solubilization of enzymatically active acyl-CoA:lysolecithin acyltransferase from thymocyte plasma membranes. The solubilized enzyme was not sedimented at 177,000 x g for 60 min and penetrated into Sepharose 6B gels. Low detergent concentration resulted in a selective extraction of the acyltransferase (about 70%) as compared to alkaline phosphatase, nucleotide pyrophosphatase, gamma-glutamyltransferase or Mg2+-ATPase (30 to 40%). The selectivity was reflected in sodium dodecyl sulfate-polyacrylamide gel electrophoresis patterns of soluble and sedimentable membrane fractions; three bands of approximately 53, 84, and 94 x 10(3) daltons were enriched in the supernatants, whereas one band of about 68 x 10(3) daltons was concentrated in the pellet. The preferential extraction of acyltransferase may be related to particularly high affinity of lysolecithin analogs for this enzyme, which at higher concentrations was competitively inhibited by these detergents. The inhibitor constants ranged from 1400 micron for the C10 analog (ET-10-H) to 80 micron for the compound with 16 carbons (ET-16-H) per aliphatic chain.
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PMID:Detergent properties of water-soluble choline phosphatides. Selective solubilization of acyl-CoA:lysolecithin acyltransferase from thymocyte plasma membranes. 42 75

Insulin receptor characteristics were examined in purified brush border membrane from the syncytiotrophoblast of the normal human placenta and quantified during membrane preparation. Insulin receptor concentration was enriched 10- to 15-fold in this preparation, and insulin receptor specific activity followed closely the enrichment values for microvillus plasma membrane markers, alkaline phosphatase, Ca2+- and Mg2+-ATPase, and 5'-nucleotidase during cell fractionation. Insulin receptor concentrations and marker enzyme analyses were compared in whole homogenate, mitochondrial, microsomal, and microvillus fractions, and these fractions were characterized by SDS-gel electrophoresis. Microvillus insulin receptor interactions were dependent on time, [125I]iodoinsulin concentration, protein, and unlabeled hormone concentrations. Competition studies with porcine insulin and [125I]iodoinsulin for this receptor revealed a curvilinear Scatchard plot. Insulinase was demonstrated at 37 C but was minimal at 24 C in the microvillus fraction. Electron microscopy of the microvillus membrane preparation revealed its composition to be mainly spherical closed membrane vesicles and brush border fragments. Sodium dodecyl sulfate polyacrylamide and isoelectric focusing gels of membrane fractions were compared. Actin was tentatively identified as a major microvillus membrane protein and was further fractionated: beta-Actin and gamma-actin were present in approximately equal concentrations. The localization of the insulin receptor in the microvillus brush border of the human placenta suggests that this receptor interacts with maternal, rather than fetal insulin.
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PMID:Characteristics of the microvillus brush border of human placenta: insulin receptor localization in brush border membranes. 75 22

Taurocholate transport was characterized in basolateral plasma membrane vesicles prepared from the livers of 14-day-old Sprague-Dawley rats using a self-generating Percoll gradient method. Liver plasma membrane protein yield, intravesicular volume, and enrichments of various marker enzymes were similar to those obtained for vesicles from adult rat liver. The basolateral marker enzyme Na+-K+-ATPase was enriched 26-fold in the suckling rat basolateral membrane fraction while the bile canalicular marker enzymes alkaline phosphatase and Mg2+-ATPase were enriched only 3- and 5-fold, respectively. The activities of marker enzymes for endoplasmic reticulum, mitochondria, or lysosomes were not enriched compared with homogenate. In the presence of an inwardly directed 100 mM Na+ gradient, vesicle accumulation of taurocholate transiently reached a concentration 1.5- to 2-fold higher than that at equilibrium ("overshoot") in suckling and adult membrane vesicles, but the initial rate of taurocholate entry and peak intravesicular accumulation were markedly decreased in suckling compared with adult membrane vesicles. In the presence of an inwardly directed 100 mM K+ gradient, the rate of uptake was slower, and no overshoot occurred in either suckling or adult rat vesicles. The decreased rate of Na+-coupled taurocholate uptake by membrane vesicles from suckling rat liver could not be explained on the basis of more rapid dissipation of the transmembrane Na+ gradient. Kinetic studies demonstrated saturable, Na+-dependent taurocholate uptake for both suckling and adult vesicles. However, the Vmax for taurocholate uptake in suckling rat vesicles was less than half of the adult rate (2.46 +/- 0.13 vs. 5.25 +/- 0.22 nmol X mg prot-1 X min-1, respectively, P less than 0.001).(ABSTRACT TRUNCATED AT 250 WORDS)
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PMID:Taurocholate transport by basolateral plasma membrane vesicles isolated from developing rat liver. 240 82


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