Gene/Protein Disease Symptom Drug Enzyme Compound
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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)

(Na+ + K+)-ATPase (ATP phosphohydrolase, EC 3.6.1.3) was purified from human cadaver renal tissue and exhibited a linear reaction rate with time. 100 g of whole kidney would yield 1--3.5 mg protein with a specific activity of 50--200 mol - kg-1 - h-1 for (Na+ + K+)-ATPase. The preparation was completely inhibited by 100 micronM ouabain with a Ki of 1.8 micronM. K+-dependent phosphatase increased during purification of (Na+ + K+)-ATPase to 7.8 mol - kg-1 - h-1. There was no detectable Mg2+-ATPase in the final preparation. Sodium dodecyl sulfate-polyacrylamide disc gel electrophoresis yielded three protein peaks of 117 000, 92 500, and 56 000 daltons. The peptide band corresponding to 92 500 daltons underwent an Na+-dependent phosphorylation with [gamma-32P]-ATP. The band at 56 000 daltons stained for glycoprotein. The Km for ATP was 0.38 mM and that for Mg2+ was 0.5 mM. The formation of ADP and inorganic phosphate from ATP was stoichiometric. The Km for Na+ in the presence of 20 mM K+ was 16 mM and the Km for K+ in the presence of 100 mM Na+ was 1.5 mM. The temperature optimum was 51degrees C and the pH optimum was 7.0. (Na+ + K+)-ATPase in whole homogenate, microsomes, and NaI-treated microsomes exhibited a slowing of reaction rate (non-linearity) with time such that the enzyme was inactive by 10--15 min of reaction. This non-linearity was eliminated during purification. The significance is discussed.
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PMID:Purification of the (Na+ + K+)-adenosine triphosphatase from human renal tissue. 1 1

Freshly isolated sarcoplasmic reticulum vesicles contain 0.05 mol of tightly bound ADP and 0.03 mol of tightly bound ATP per mol of Ca2+, Mg2+-ATPase (ATP phosphohydrolase, EC 3.6.1.3). These values were increased to 0.1-0.2 mol ADP and 0.2-0.3 mol ATP per mol of ATPase after incubation of vesicles in the presence of MgATP and Ca2+ at 25 degrees C and pH 7.0. Half-maximal enrichment of tightly bound nucleotides was obtained with 2.5 mM ATP and 0.32 microM free Ca2+. Uncoupling of calcium transport from ATPase activity by mild acidic conditions or with ethylene glycol bis(beta-aminoethyl ether)-N,N,N',N'-tetraacetic acid at pH 7.0 decreased the ability of the membranes to be enriched with tightly bound nucleotides and also decreased the content of tightly bound nucleotides of previously enriched membranes. Tightly bound [3H]nucleotides could only be partially displaced by reincubation under enrichment conditions. Tightly bound nucleotides are associated with energized calcium translocation but do not appear to be directly involved in the catalytic cycle.
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PMID:Occurrence and role of tightly bound adenine nucleotides in sarcoplasmic reticulum of rabbit skeletal muscle. 4 Feb 28

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

Different antiarrhythmic agents such as quinidine, procaine amide, and lodocaine at 1 mM concentrations were found to depress the ability of an isolated perfused rat heart to generate contractile force. Quinidine, but not procaine amide or lidocaine, decreased calcium uptake by both mitochondrial and microsomal fractions at different concentrations of calcium. The mitochondrial phosphorylation rate, respiratory control index, and state 3 oxygen consumption, but not ADP:O ratio and state 4 oxygen consumption, were depressed by only quinidine. None of these agents had any effect on myofibrillar Mg2+-ATPase or Ca2+-stimulated ATPase activities. On the other hand, sarcolemmal Mg2+-ATPase and Ca2+-ATPase activities, but not Na+-K+-ATPase activity, were increased by all these drugs. The sarcolemmal adenylate cyclase (EC 4.6.1.1) activity was decreased by quinidine only. These results suggest some similarities and differences in the sites of action of quinidine, procaine amide, and lidocaine within the myocardium.
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PMID:Subcellular and functional effects of quinidine, procaine amide, and lidocaine on rat myocardium. 13 Sep 65

Adenosine triphosphate (ATP) hydrolysis catalyzed by the plasma membrane (Na+,K+)ATPase isolated from several sources was inhibited by Mg+, provided that K+ and ATP were also present. Phosphorylation of the adenosine triphosphatase (ATPase) by ATP and by inorganic phosphate was also inhibited, as was p-nitrophenyl phosphatase activity. (Ethylenedinitrilo)tetraacetic acid (EDTA) and catecholamines protected from and reversed the inhibition of ATP hydrolysis by Mg2+, K+ and ATP. EDTA was protected by chelation of Mg2+ but catecholamines acted by some other mechanism. The specificities of various nucleotides as inhibitors (in conjunction with Mg2+ and K+) and as substrates for the (Na+, K+) ATPase were strikingly different. ATP, ADP, beta,gamma-CH2-ATP and alpha,beta-CH2-ADP were active as inhibitors, whereas inosine, cytidine, uridine, and guanosine triphosphates (ITP, CTP, UTP, and GTP) and adenosine monophosphate (AMP) were not. On the other hand, ATP and CTP were substrates and beta,gamma-NH-ATP was a competitive inhibitor of ATP hydrolysis, but not an inhibitor in conjunction with Mg2+ and K+. The Ca2+-ATPase from sarcoplasmic reticulum and F1, the Mg2+-ATPase from the inner mitochondrial membrane, were also inhibited by Mg2+. Catecholamines reversed inhibition of the Ca2+-ATPase, but not that of F1.
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PMID:Reversible inhibition of (Na+, K+) ATPase by Mg2+, adenosine triphosphate, and K+. 13 42

Kinetic measurement of the reaction of dynein ATPase (ATP phosphohydrolase, EC 3.6.1.3) extracted from the gills of Mytilus edulis shows that in the presence of Mg2+ there is a very rapid initial liberation of Pi from the dynein-ATP system, followed by a slower liberation in the steady state. In view of following results, we have confirmed that this phenomenon is not due to the accumulation of end products, a fall in substrate concentration, nor to the presence of labile impurities in ATP but is due to the catalytic activity of dynein ATPase. 1. The replacement of native dynein by heat denatured dynein or other kinds of Mg2+-ATPase could not produce such a burst phenomenon under the same condition. 2. Both the rate of initial burst and that of steady state were proportional to enzyme content over a wide range under our standard condition. 3. Initial burst was also observed under the constant ATP level by using a ATP generate system. 4. Preincubation of dynein with Pi prior to initiation of the reaction did not eliminate the initial burst. Some properties of the initial rapid liberation of dynein ATPase were also examined. These are shown below. 5. The free ADP liberation did not show any initial burst though the Pi liberation did in the initial phase and the rate of free ADP liberation was almost equal to that of Pi liberation of the steady state. 6. Mg2+ was more effective than Ca2+ for the appearance of the initial burst while the liberation of Pi in the steady state was activated more by Ca2+ than by Mg2+. The addition of K+ in the presence of Mg2+ resulted in a marked increase of Pi liberation in the steady state but not in the initial state. 7. The activation energy of the initial burst was 9.7 kcal, which is slightly smaller than that of myosin ATPase.
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PMID:Studies on the initial phase of dynein ATPase activity. 13 33

Oviductal secretions include an ATPase (EC 3.6.1.3) that is transferred from the outer surface of the secretory cells to the surface of the ovulated oocyte. The enzyme has been purified and is a highly labile, very high molecular weight lipoprotein complex (greater than 4-10(6)). It consists of 47% protein and 53% lipid. Lipid composition is limited to phosphatidylcholine, phosphatidylethanolamine and sphingomyelin. The basic protein subunit has a molecular weight of 170 000. The enzyme exhibits many of the characteristics of ectoenzyme ATPase. The enzyme is Mg2+ or Ca2+ dependent; the Mg2+-ATPase has pH optima at 6.0 and 7.8 and the Ca2+-ATPase at 9.0. Substrate specificity is limited to ATP with lesser activity towards GTP, CTP, UPT and ADP. Km for ATP is 0.88 mM and the enzyme is inhibited at substrate concentrations greater than 3 mM ATP.
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PMID:Purification and characterization of an extracellular ATPase from oviductal secretions. 14 Jul 3

The dicyclohexylcarbodiimide-sensitive ATPase from spinach chloroplast has been isolated. On sodium dodecyl sulfate gels, seven different polypeptides were seen. Five of these polypeptides coincided with the CF1 subunits, a 7,500-dalton peptide was identified as the proteolipid which interacts with [14C]dicyclohexylcarbodiimide, and there was a 15,500-dalton hydrophobic polypeptide with unknown function. In two-dimentional gels, two additional peptides were resolved, one 17,500 daltons (co-migrating in sodium dodecyl sulfate gels with subunit delta) and one 13,500 daltons (co-migrating with subunit epsilon). Reconstitution was obtained by freezing and thawing the complex with a crude mixture of phospholipids. After reconstitution the complex catalyzed 32P1-ATP exchange (rates of 200 to 400 nmoles x mg-1 x min-1) and ATP formation during acid-to-base transition. These reactions were inhibited by dicyclohexylcarbodiimide and uncouplers. Uncouplers at low concentrations stimulated and at high concentrations inhibited the Mg2+-ATPase activity. ATP hydrolysis and 32P1-ATP exchange were catalyzed by the complex in the presence of either Mg2+ or Mn2+ but not with Ca2+ or Co2+. ATP and GTP were substrates for the exchange reaction but not ADP or CTP.
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PMID:Purification and reconstitution of the N,N'-dicyclohexylcarbodiimide-sensitive ATPase complex from spinach chloroplasts. 15 58

(1) Photophosphorylation, Ca2+-ATPase and Mg2+-ATPase activities of isolated chloroplasts were inhibited 55--65% when the chemical potential of water was decreased by dehydrating leaves to water potentials (psi w) of --25 bars before isolation of the plastids. The inhibition could be reversed in vivo by rehydrating the leaves. (2) These losses in activity were reflected in coupling factor (CF1) isolated from the leaves, since CF1 from leaves with low psi w had less Ca2+-ATPase activity than control CF1 and did not recouple phosphorylation in CF1-deficient chloroplasts. In contrast, CF1 from leaves having high psi w only partially recoupled phosphorylation by CF1-deficient chloroplasts from leaves havig low psi w. This indicated that low psi w affected chloroplast membranes as well as CF1 itself. (3) Coupling factor from leaves having low psi w had the same number of subunits, and the same electrophoretic mobility, and could be obtained with the same yields as CF1 from control leaves. However, direct measurements of fluorescence polarization, ultraviolet absorption, and circular dichroism showed that CF1 from leaves having low psi w differed from control CF1. The CF1 from leaves having low psi w also had decreased ability to bind fluorescent nucleotides (epsilon-ATP and epsilon-ADP). (4) Exposure of isolated CF1 to low psi w in vitro by preincubation in sucrose-containing media inhibited the Ca2+-ATPase activity of the protein in subsequent assays without sucrose. Inclusion of 5 or 10 mM Mg2+ in the preincubation medium markedly inhibited Ca2+-ATPase activity. (5) These results show that CF1 undergoes changes in cells which alter its phosphorylating ability. Since low cell psi w changed the spectroscopic properties but not other protein properties of CF1, the changes were most likely caused by altered confurn, photophosphorylation. The inhibition of ATPase activity in CF1 in vitro at low psi w and high ion concentration mimicked the change in activity seen in vivo.
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PMID:Conformation and activity of chloroplast coupling factor exposed to low chemical potential of water in cells. 15 20

We have shown that the rat liver plasma membrane has at least two (Ca2+-Mg2+)-ATPases. One of them has the properties of a plasma membrane Ca2+-pump (Lin, S.-H. (1985) J. Biol. Chem. 260, 7850-7856); the other one, which we have purified (Lin, S.-H., and Fain, J.N. (1984) J. Biol. Chem. 259, 3016-3020) and characterized (Lin, S.-H. (1985) J. Biol. Chem. 260, 10976-10980) has no established function. In this study we present evidence that the purified (Ca2+-Mg2+)-ATPase is a plasma membrane ecto-ATPase. In hepatocytes in primary culture, we can detect Ca2+-ATPase and Mg2+-ATPase activities by addition of ATP to the intact cells. The external localization of the active site of the ATPase was confirmed by the observation that the Ca2+-ATPase and Mg2+-ATPase activities were the same for intact cells, saponin-treated cells, and cell homogenates. Less than 14% of total intracellular lactate dehydrogenase, a cytosolic enzyme, was released during a 30-min incubation of the hepatocytes with 2 mM ATP. This indicates that the hepatocytes maintained cytoplasmic membrane integrity during the 30-min incubation with ATP, and the Ca2+-ATPase and Mg2+-ATPase activity measured in the intact cell preparation was due to cell surface ATPase activity. The possibility that the ecto-Ca2+-ATPase and Mg2+-ATPase may be the same protein as the previously purified (Ca2+-Mg2+)-ATPase was tested by comparing the properties of the ecto-ATPase with those of (Ca2+-Mg2+)-ATPase. Both the ecto-ATPase and the (Ca2+-Mg2+)-ATPase have broad nucleotide-hydrolyzing activity, i.e. they both hydrolyze ATP, GTP, UTP, CTP, ADP, and GDP to a similar extent. The effect of Ca2+ and Mg2+ on the ecto-ATPase activity is not additive indicating that both Ca2+- and Mg2+-ATPase activities are part of the same enzyme. The ecto-ATPase activity, like the (Ca2+-Mg2+)-ATPase, is not sensitive to oligomycin, vanadate, N-ethylmaleimide and p-chloromercuribenzoate; and both the ecto-ATPase and purified (Ca2+-Mg2+)-ATPase activities are insensitive to protease treatments. These properties indicate that the previously purified (Ca2+-Mg2+)-ATPase is an ecto-ATPase and may function in regulating the effect of ATP and ADP on hepatocyte Ca2+ mobilization (Charest, R., Blackmore, P.F., and Exton, J.H. (1985) J. Biol. Chem. 260, 15789-15794).
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PMID:Two Ca2+-dependent ATPases in rat liver plasma membrane. The previously purified (Ca2+-Mg2+)-ATPase is not a Ca2+-pump but an ecto-ATPase. 245 81


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