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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)

The effects of the alpha 1-adrenergic agonist phenylephrine (PE) and the phorbol ester 4 beta-phorbolmyristate-acetate (PMA) on sodium pump function were studied in the rat liver. In order to distinguish between direct and indirect influences, ouabain-sensitive 86Rb uptake by intact liver slices was compared with ouabain-sensitive Na+/K+-ATPase activity in plasma membranes isolated from PE and PMA-perfused livers. At a buffer Ca2+ level of 2.5 mmol/l, PE (10 mumol/l) caused an initial stimulation of both 86Rb uptake and Na+/K+-ATPase activity followed at 5 min by a decrease in both activities. Both actions were blocked by the alpha 1-antagonist prazosin. The decrease in ouabain-sensitive Na+/K+-ATPase was paralleled by an increase in Mg2+ ATPase activity. At a Ca2+ level of 1.5 mmol/l, PE stimulation of 86Rb uptake and Na+/K+-ATPase was sustained, and the inhibitory component was not expressed. PMA (4 mumol/l) reduced 86Rb uptake and Na+/K+-ATPase and similar to PE, this inhibition was paralleled by an increase of Mg2+-ATPase activity. 4 alpha-PMA, which does not activate protein kinase C, failed to influence 86Rb uptake or Na+/K+-ATPase. These results demonstrate that PE and PMA effects on ouabain-sensitive 86Rb uptake are preserved in isolated membranes, indicating a direct influence on the Na+/K+-ATPase. A role for protein kinase C in modulating sodium pump activity is suggested.
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PMID:Influence of alpha 1-adrenergic receptor stimulation and phorbol esters on hepatic Na+/K+-ATPase activity. 290 84

Alkaline phosphatase (ALPase) and Mg2+-activated ATPase (Mg2+-ATPase) activities were demonstrated in human brain tumors by light and electron microscopy. Four cases of glioma, i.e., two cases of astrocytoma, grade II, and two cases of glioblastoma, were used as materials. At the light microscopic level, Mg2+-ATPase activity was observed in the capillary wall and glial cells of both astrocytoma and glioblastoma. ALPase activity was restricted to the capillary wall. Its activity was stronger in glioblastoma than in astrocytoma. By electron microscopy, in astrocytoma, reaction product representing Mg2+-ATPase activity was distributed in the plasma membranes of endothelial cells and pericytes. Activity was primarily localized at the abluminal surface of endothelial cells and the surface of pericytes facing endothelium. The plasma membrane of glial cells was also positive. ALPase activity revealed essentially the same distribution pattern in blood vessels as above. In glioblastoma, on the other hand, activities of both phosphatases were markedly positive on the luminal surface of the plasma membrane of endothelial cells. They were much stronger than those along the abluminal endothelial surface. Phosphatase activities in brain tumor appear to change in localization pattern in association with glioma malignancy. This might reflect a functional aspect of changes in blood-brain barrier in glioma.
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PMID:Phosphatase activities in human glioma cells as revealed by light and electron microscopy--a preliminary study. 293 40

An inhibitor protein of synaptic plasma membrane (Ca2+ + Mg2+)-ATPase was purified to apparent homogeneity from rat cerebrum by a molecular weight cut followed by chromatography of cytosol proteins with molecular weights between 10 000 and 3500 on DEAE-Sephadex at pH 5.2. The inhibitor could be partially inactivated by proteinases and dithiothreitol, but was heat-stable. Gel filtration gave a molecular weight of about 6000. Like the (Ca2+ + Mg2+)-ATPase inhibitor protein isolated from erythrocytes, the inhibitor from brain contains a characteristic high proportion of glutamic acid (36%) and glycine (37%) residues. Synaptic plasma membrane Mg2+-ATPase and microsomal membrane (Ca2+ + Mg2+)-ATPase did not respond to the inhibitor. Synaptic plasma membrane and erythrocyte membrane (Ca2+ + Mg2+)-ATPases, however, were affected. Inhibitory influence on synaptic membrane (Ca2+ + Mg2+)-ATPase was reversible, since inhibition could be relieved upon removal of inhibitor from saturable sites on the membrane. The inhibitor is not a calmodulin-binding protein, since the concentration of calmodulin for half-maximal activation of the ATPase was unaffected by its presence. Mode of inhibition of the (Ca2+ + Mg2+)-ATPase by the inhibitor was non-competitive.
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PMID:An endogenous inhibitor protein of synaptic plasma membrane (Ca2+ + Mg2+)-ATPase. 293 75

Increasing the levels of Mg2+ concentrations outside the sarcoplasmic reticulum (SR) vesicles larger than the ATP concentrations results in a decrease of the Ca2+/Mg2+-ATPase affinity to Ca2+. When SR vesicles are loaded with varying concentrations of magnesium in the inside and the same concentration on the outside, the initial rate of calcium transport into the SR is increased by up to 50% with K0.5 (Mg2+) = 0.127 mM. During active calcium transport, we found no evidence of a magnesium influx. However, the data indicate that magnesium is extruded from SR vesicles during calcium uptake, but the magnitude of magnesium efflux is too small (8%) to account for the cation counter transport of calcium.
Magnesium 1985
PMID:Trans-magnesium dependency of ATP-dependent calcium uptake into sarcoplasmic reticulum of skeletal muscle. 293 89

The ATP-dependent uptake of Ca2+ by rat liver microsomal fraction is dependent upon Mg2+. Studies of the Mg2+ requirement of the underlying microsomal Ca2+-ATPase have been hampered by the presence of a large basal Mg2+-ATPase activity. We have examined the effect of various Mg2+ concentrations on Mg2+-ATPase activity, Ca2+ uptake, Ca2+-ATPase activity and microsomal phosphoprotein formation. Both Mg2+-ATPase activity and Ca2+ uptake were markedly stimulated by increasing Mg2+ concentration. However, the Ca2+-ATPase activity, measured concomitantly with Ca2+ uptake, was apparently unaffected by changes in the Mg2+ concentration. In order to examine the apparent paradox of Mg2+ stimulation of Ca2+ uptake but not of Ca2+-ATPase activity, we examined the formation of the Ca2+-ATPase phosphoenzyme intermediate and formation of a Mg2+-dependent phosphoprotein, which we have proposed to be an attribute of the Mg2+-ATPase activity. We found that Ca2+ apparently inhibited formation of the Mg2+-dependent phosphoprotein both in the absence and presence of exogenous Mg2+. This suggests that Ca2+ may inhibit (at least partially) the Mg2+-ATPase activity. However, inclusion of the Ca2+ inhibition of Mg2+-ATPase activity in the calculation of Ca2+-ATPase activity reveals that this effect is insufficient to totally account for the stimulation of Ca2+ uptake by Mg2+. This suggests that Mg2+, in addition to stimulation of Ca2+-ATPase activity, may have a direct stimulatory effect on Ca2+ uptake in an as yet undefined fashion. In an effort to further examine the effect of Mg2+ on the microsomal Ca2+ transport system of rat liver, the interaction of this system with Sr2+ was examined. Sr2+ was sequestered into an A23187-releasable space in an ATP-dependent manner by rat liver microsomal fraction. The uptake of Sr2+ was similar to that of Ca2+ in terms of both rate and extent. A Sr2+-dependent ATPase activity was associated with the Sr2+ uptake. Sr2+ promoted formation of a phosphoprotein which was hydroxylamine-labile and base-labile. This phosphoprotein was indistinguishable from the Ca2+-dependent ATPase phosphoenzyme intermediate. Sr2+ uptake was markedly stimulated by exogenous Mg2+, but the Sr2+-dependent ATPase activity was unaffected by increasing Mg2+ concentrations. Sr2+ uptake and Sr2+-dependent ATPase activity were concomitantly inhibited by sodium vanadate. In contrast to Ca2+, Sr2+ had no effect on Mg2+-dependent phosphoprotein formation. Taken together, these data indicate that Mg2+ stimulated Ca2+ and Sr2+ transport by increasing the Ca2+ (Sr2+)/ATP ratio.(ABSTRACT TRUNCATED AT 400 WORDS)
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PMID:The effect of Mg2+ on hepatic microsomal Ca2+ and Sr2+ transport. 293 94

Audiogenic seizure (AGS)-susceptible DBA/2 (D2) mice have a significant reduction in brain Ca2+-ATPase activity compared to AGS-resistant C57BL/6 (B6) mice. This reduction is inherited together with AGS susceptibility in B6 X D2 recombinant inbred strains. The Ca2+-ATPase reduction occurs in microsomes and synaptosomes, but not in mitochondria. This enzyme activity is measured at a high Ca2+ concentration (2 mM) with no added Mg2+ or EGTA. We further studied this Ca2+-ATPase activity and a Mg2+-dependent (Ca2+ + Mg2+)-ATPase activity in synaptic plasma membranes (SPM) from the B6 and D2 strains. Using EGTA or CDTA to adjust free Ca2+ concentrations, we measured Ca2+-ATPase activities at Ca2+ concentrations from 0.8 microM to 436 microM. The Ca2+-ATPase activity is consistently lower in the D2 than in the B6 SPM over all Ca2+ concentrations. The basal Mg2+-ATPase activity measured at 2 mM MgCl2, is also lower in SPM of D2 than B6 mice. Calcium stimulates the basal Mg2+-ATPase activity to the same extent in the SPM of the B6 and the D2 mice. Maximum stimulation in both strains occurs at 150 microM added CaCl2 (buffered with 100 microM EGTA). Higher Ca2+ concentrations inhibit this ATPase activity similarly in both strains. The EGTA-EDTA washing of SPM significantly reduces by 50% of the (Ca2+ + Mg2+)-ATPase activities of both strains, whereas calmodulin treatment restored these activities. Neither of these treatments, however, has any noticeable effects on the Ca2+-ATPase activities of the strains.(ABSTRACT TRUNCATED AT 250 WORDS)
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PMID:Calcium ATPase activities in synaptic plasma membranes of seizure-prone mice. 293 83

A membrane fraction enriched in endoplasmic reticulum was prepared from rat parotid glands by using sucrose-gradient centrifugation. The fraction showed a 10-fold increase in specific activity of NADPH: cytochrome c reductase activity over that of tissue homogenates and minimal contamination with plasma membranes or mitochondria. The endoplasmic reticulum fraction possessed both Mg2+ -stimulated ATPase as well as Ca2+, Mg2+-ATPase [( Ca2+ + Mg2+)-stimulated ATPase]activity. The Ca2+, Mg2+-ATPase required 2-5 mM-Mg2+ for optimal activity and was stimulated by submicromolar concentrations of free Ca2+. The Km for free Ca2+ was 0.55 microM and the average Vmax. was 60 nmol/min per mg of protein. The Km for ATP was 0.11 mM. Other nucleotides, such as GTP, CTP or ADP, could not substitute for ATP in supporting the Ca2+-activated nucleotidase activity. Increasing the K+ concentration from 0 to 100 mM caused a 2-fold activation of the Ca2+, Mg2+-ATPase. Trifluoperazine, W7 [N-(6-aminohexyl)-5-chloronaphthalene-1-sulphonamide] and vanadate inhibited the enzyme. The concentration of trifluoperazine and vanadate required for 50% inhibition of the ATPase were 52 microM and 28 microM respectively. Calmodulin, cyclic AMP, cyclic AMP-dependent protein kinase and inositol 1,4,5-trisphosphate had no effect on the ATPase. The properties of the Ca2+, Mg2+ -ATPase were distinct from those of the Mg2+-ATPase, but comparable with those reported for the parotid endoplasmic-reticulum Ca2+-transport system [Kanagasuntheram & Teo (1982) Biochem. J. 208, 789-794]. The results suggest that the Ca2+, Mg2+-ATPase is responsible for driving the ATP-dependent Ca2+ accumulation by this membrane.
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PMID:The (Ca2+ + Mg2+)-stimulated ATPase of the rat parotid endoplasmic reticulum. 294 71

The effect of a single administration of morphine sulfate (15 mg/kg, s.c. or 30 mg/kg, i.p., 30 min) on Ca2+-stimulated Mg2+-dependent ATPase activity was investigated in synaptosomal plasma membranes (SPM) prepared from rat cortex. Morphine produced a significant decrease in Ca2+,Mg2+-ATPase activity in synaptosomal fractions (SPM 1 + 2) known to contain a high density of opiate receptors and calmodulin-dependent Ca2+,Mg2+-ATPase. However, in another subpopulation (SPM 3) that contains fewer opiate receptors and less enzyme activity, no such decrease in the enzyme activity was observed after the opiate administration. The decrease in Ca2+,Mg2+-ATPase activity seen in SPM 1 + 2 was specifically antagonized by the opiate antagonist naloxone hydrochloride (2 mg/kg, s.c.) when given 15 min before morphine administration. Mg2+-ATPase was not altered either by morphine or by a naloxone-morphine combination. These findings give further evidence for the role of intracellular Ca2+ in mediating many of the acute effects of opiates.
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PMID:Effects of opiates on high-affinity Ca2+,Mg2+-ATPase in brain membrane subfractions. 294 93

The phospholipid requirement for Ca2+-stimulated, Mg2+-dependent ATP hydrolysis (Ca2+/Mg2+-ATPase) and Mg2+-stimulated ATP hydrolysis (Mg2+-ATPase) in rat brain synaptosomal membranes was studied employing partial delipidation of the membranes with phospholipase A2 (Hog pancreas), phospholipase C (Bacillus cereus) and phospholipase D (cabbage). Treatment with phospholipase A2 caused an increase in the activities of both Ca2+/Mg2+-ATPase and Mg2+-ATPase whereas with phospholipase C treatment both the enzyme activities were inhibited. Phospholipase D treatment had no effect on Ca2+/Mg2+-ATPase but Mg2+-ATPase activity was inhibited. Inhibition of Mg2+-ATPase activity after phospholipase C treatment was relieved with the addition of phosphatidylinositol-4,5-bisphosphate (PIP2) and to a lesser extent with phosphatidylinositol-4-phosphate (PIP) and phosphatidylcholine (PC). Phosphatidylserine (PS), phosphatidic acid (PA), PIP and PIP2 brought about the reactivation of Ca2+/Mg2+-ATPase. Phosphatidylinositol (PI) and PA inhibited Mg2+-ATPase activity. Kms for Ca2+ (0.47 microM) and Mg2+ (60 microM) of the enzyme were found to be unaffected after treatment with the phospholipases.
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PMID:Phospholipid requirement of Ca2+-stimulated, Mg2+-dependent ATP hydrolysis in rat brain synaptic membranes. 294 70

Rat brain microsomal Mg2+-ATPases with two distinct activities: ethacrynic acid (EA) highly sensitive and EA less sensitive Mg2+-ATPase activities were solubilized by the combined treatment with 10 mM 3-(3-chlolamidopropyl)-dimethylammonio-1-propane-sulfate (CHAPS) and 30 mM octyl-beta-D-glucoside. The solubilized enzymes had properties similar to those of the membrane-bound enzyme in microsomes with respect to the sensitivity to EA and Cl-, although the optimal pH and the affinity to ATP were slightly altered after the solubilization. Fast protein liquid chromatography of the solubilized enzymes on an anion-exchanger (Mono Q) column with a linear NaCl gradient (0-1.0 M) yielded separate peaks for EA highly sensitive and EA less sensitive Mg2+-ATPase activities at 0.1 and 0.35 M NaCl, respectively. Polyacrylamide gradient gel electrophoresis of the samples from the peak-fractions of EA highly sensitive and EA less sensitive Mg2+-ATPase activities yielded prominent bands at 600 and 70 kDa, respectively. These results indicate that EA highly sensitive Mg2+-ATPase is solubilized and separated from EA less sensitive Mg2+-ATPase as a large enzyme molecule with anion-sensitive sites.
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PMID:Solubilization and separation of ethacrynic acid (EA) highly sensitive and EA less sensitive Mg2+-ATPases in the rat brain. 295 25


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