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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 requirement of actual splitting of ATP for endocytosis in erythrocyte ghosts has been confirmed by use of the ATP analog, 5'-adenylylimidodiphosphate, (AMP-P(NH)P). This compound, in which the oxygen connecting the beta and gamma phosphorus atoms was replaced by an NH group, did not cause endocytosis nor was it a substrate for ATPase activity. AMP-P(NH)P was a competitive inhibitor both for the endocytosis and the Mg2+-ATPase activities. The K1 of AMP-P(NH)P for Mg2+ ATPase activity was 2.0 - 10-4 M and, while the Km of ATP for this activity was also 2.0 - 10-4 M indicating nearly identical affinities of ATP and AMP-P(NH)P for the active site. ADP, or ADP plus orthophosphate, did not cause endocytosis, showing that endocytosis was not due to binding of the products of ATP hydrolysis. Sodium or potassium ion or ouabain had no effect on endocytosis, which eliminated the possibility of involvement of the Na+, K+ ATPase in the endocytosis process. Calcium could not be substituted for magnesium; rather it inhibited endocytosis at the concentration of 1 - 10-3 M. EGTA relieved the inhibitory effect of Ca, which indicated that the binding of calcium to the membrane was reversible. These experimental results reaffirm the conclusion that ATP must be split to engender endocytosis under these conditions. Some characteristic parameters of the hemoglobin-free porcine erythrocyte ghosts were studied in order to characterize the system more adequately.
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PMID:Energy-dependent endocytosis in erythrocyte ghosts. IV. Effects of Ca2+, Na+ +K+, and 5'-adenylylimidodiphosphate. 12 70

Erythrocytes and their isolated membranes display ATP-dependent endocytosis. To localize the enzymes responsible for this phenomenon, the erythrocyte membranes (ghosts) were fractionated under conditions which retained ATPase activity. Fractionation of the ghosts resulted in three fractions: spectrin-actin, the peripheral proteins soluble in high salt, and the smooth membrane containing integral proteins. On the average, 87% of the protein and 88% of the phosphorus of the original ghosts were recovered in these fractions, and all of the kinds of ATP-splitting activities of the membrane were recovered in the smooth membrane. A tiny ATPase activity, detectable by special methodology in spectrinactin, could have been due to contamination with membranous material. Although the purified spectrin-actin did not have a significant ATPase of its own, it stimulated the Ca2+, Mg2+-ATPase of the smooth membrane significantly, suggesting a cooperative interaction between these two fractions. This segregation of the ATPase activities into the smooth membrane, combined with the energy dependence of endocytosis, showed that the smooth membrane must be involved in the energy production for endocytosis. The possibility that the spectrin-actin filaments cooperate with a myosinlike ATPase in the membrane to generate membrane movements is discussed.
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PMID:Peripheral proteins and smooth membrane from erythrocyte ghosts. Segregation of ATP-utilizing enzymes into smooth membrane. 14 43

Renal proximal tubule cells adapt to dietary phosphate (Pi) restriction by increasing Pi transport independent of parathyroid hormone, vitamin D metabolites, or serum Ca2+. To determine the underlying cellular mechanism(s), brush border (BBM) and basolateral membranes (BLM) were isolated from growing male rats fed a synthetic diet containing variable levels of Pi (0.1-1.4%). Dietary Pi restriction was without effect on either BBM or BLM total lipid phosphorus, individual phospholipid species, or BLM Na+-K+-ATPase specific activity. However, dietary Pi restriction (0.1 vs. 1.0%) did cause a significant reduction in BBM but not BLM cholesterol (0.45 vs. 0.41 mumol/mg protein). Brush border membrane cholesterol was inversely correlated with the tubular reabsorption of Pi (r = 0.77, P less than 0.01) over a broad range (99.9-46.2%). Arrhenius analysis of two intrinsic BBM enzymes revealed a significant reduction in the breakpoint temperature for alkaline phosphatase but no change for Mg2+-ATPase. Fluorescence polarization studies showed increased BBM inner core fluidity due to an alteration in neutral lipids but not phospholipid, fatty acid, or protein membrane components. These data demonstrate that the BBM can regulate its cholesterol content independent of the BLM. Furthermore, they suggest that adaptation to dietary Pi restriction involves a reduction in BBM cholesterol, which may be mediated by an increase in membrane fluidity.
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PMID:Renal apical membrane cholesterol and fluidity in regulation of phosphate transport. 316 Feb 47

The content of adenine nucleotides, ATPase activity, the amount of total and inorganic phosphorus in the carp liver mitochondria were studied as affected by CO2 high concentrations. It is shown that during adaptation to the CO2 higher level in the medium the amount of ATP in fishes undergoes the most significant changes. The organism response to the effect of carbon dioxide depends on its concentration in the medium and time of its action. When fishes were for 24h under conditions of the 0.4mM CO2 concentration, the ATP content in the carp liver mitochondria surpasses the control level and under conditions the 0.8 mM CO2 concentration it reaches the control level. The presence of 0.4 and 0.8 mM CO2 concentration decreases the ATP content 7 days later. The amount of inorganic phosphorus in the liver mitochondria of experimental fishes undergoes similar changes. An increase in the CO2 concentration in the water medium up to 0,4 and 0,8 mM inhibits Na+, K+, Mg2+-ATPase in fish organelles, the inhibition being more pronounced in a trial with 0.8 mM CO2.
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PMID:[Peculiarities of phosphoric compound metabolism in liver mitochondria of carp adapted to higher concentrations of CO2 in water]. 624 95

Plasma membranes were isolated from normal thymocytes of Wistar-King-A rats and from Moloney virus-induced rat thymic leukemias (RML11 and RML30 cells) using a simplified method developed by us. All the isolated plasma membranes were electron-microscopically pure and enriched in the specific activities of (Na+ + K+)-ATPase, Mg2+-ATPase and 5'-nucleotidase in comparison with those of the corresponding whole cell homogenates. These plasma membranes as well as the original cells were analyzed for phopholipid composition and contents of phospholipid, cholesterol and plasmalogen. There was no difference in the phospholipid composition among the three plasma membranes. However, all the plasma membranes were deficient in sphingomyelin, namely, 1.8% for the normal thymocytes, 2.2% for the RML11 cells and 1.9% for the RML30 cells as percentage of the total phospholipid phosphorus. The contents of phospholipid (mumol per mg protein), cholesterol (mumol per mg protein) and plasmalogen (mol% to phospholipid) of the plasma membranes from both lines of malignant cells were lower than those of the normal thymocyte membranes. The molar ratio of cholesterol to phospholipid of the malignant cell membranes was also lower than that of the normal membranes, because in the former membranes the degree of decrease in the cholesterol content was higher than that in phospholipid content.
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PMID:Lipids of plasma membranes from rat thymic lymphoid cells: deficiency of sphingomyelin. 696 38

Galactosaemia is an inborn error of metabolism characterized by irreversible damage to neural tissue. To evaluate whether galactose metabolic disorders, (e.g. classical galactosaemia, galactokinase deficiency galactosaemia), is implicated for alterations of brain Mg2+-ATPase activity, various concentrations (1-16 mM) of galactose, galactose-1-phosphate, galactitol, glucose-1-phosphate or glucose were preincubated with whole brain homogenates of suckling rats at 37 degrees for 1 hr. Mg2+-ATPase activities were determined according to Bowler & Tirri's (1974). Galactose-1-phosphate or glucose-1-phosphate excessively activated the brain Mg2+-ATPase in a concentration-dependent way. Additionally, galactitol, galactose or glucose stimulated the enzyme up to 35-45% (P < 0.001) at concentrations >4 mM. A mixture of galactose-1-phosphate (2 mM), glactitol (2 mM) and galactose (4 mM), concentrations commonly found in blood and brain of untreated patients with classical galactosaemia, resulted in a 500% enzyme activation (P < 0.001) as compared to control. Moreover, a mixture of galactitol (2 mM) and galactose (1 mM), concentrations measured in patients with galactokinase deficiency, caused an enzyme stimulation (35%, P < 0.001). These findings suggest: a) The great Mg2+-ATPase activation by galactose-1-phosphate or glucose-1-phosphate may be due to the epimer of galactose and the presence of phosphorus. b) The brain Mg2+-ATPase stimulation by galactose and its derivatives could be toxic by modulating the Mg2+ concentration, the ATP availability, the activity of other ATP- and Mg2+-dependent enzymes as well as the rates of protein synthesis and cell growth.
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PMID:The in vitro effects of galactose and its derivatives on rat brain Mg2+-ATPase activity. 1257 32