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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 (Na+ +K+)-activated, Mg2+-dependent ATPase from rabbit kidney outer medulla was prepared in a partially inactivated, soluble form depleted of endogenous phospholipids, using deoxycholate. This preparation was reactivated 10 to 50-fold by sonicated liposomes of phosphatidylserine, but not by non-sonicated phosphatidylserine liposomes or sonicated phosphatidylcholine liposomes. The reconstituted enzyme resembled native membrane preparations of (Na+ +K+)-ATPase in its pH optimum being around 7.0, showing optimal activity at Mg2+:ATP mol ratios of approximately 1 and a Km value for ATP of 0.4 mM. Arrhenius plots of this reactivated activity at a constant pH of 7.0 and an Mg2+: ATP mol ratio of 1:1 showed a discontinuity (sharp change of slope) at 17 degrees C, with activation energy (Ea) values of 13-15 kcal/mol above this temperature and 30-35 kcal below it. A further discontinuity was also found at 8.0 degrees C and the Ea below this was very high (greater than 100 kcal/mol). Increased Mg2+ concentrations at Mg2+:ATP ratios in excess of 1:1 inhibited the (Na+ +K+)-ATPase activity and also abolished the discontinuities in the Arrhenius plots. The addition of cholesterol to phosphatidylserine at a 1:1 mol ratio partially inhibited (Na+ +K+)-ATPase reactivation. Arrhenius plots under these conditions showed a single discontinuity at 20 degrees C and Ea values of 22 and 68 kcal/mol above and below this temperature respectively. The ouabain-insensitive Mg2+-ATPase normally showed a linear Arrhenius plot with an Ea of 8 kcal/mol. The cholesterol-phosphatidylserine mixed liposomes stimulated the Mg2+-ATPase activity, which now also showed a discontinuity at 20 degrees C with, however, an increased value of 14 kcal/mol above this temperature and 6 kcal/mol below. Kinetic studies showed that cholesterol had no significant effect on the Km values for ATP. Since both cholesterol and Mg2+ are known to alter the effects of temperature on the fluidity of phospholipids, the above results are discussed in this context.
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PMID:Alterations in phospholipid-dependent (Na+ +K+)-ATPase activity due to lipid fluidity. Effects of cholesterol and Mg2+. 0 90

Adenosine 5'-triphosphate (ATP) synthesis driven by an artificially imposed membrane potential in right-side-out membrane vesicles of Escherichia coli was investigated. Membrane vesicles prepared in the presence of adenosine diphosphate were loaded with K+ by incubation with 0.5 M potassium phosphate. Addition of valinomycin resulted in the synthesis of 0.2 to 0.3 nmol of ATP/mg of membrane protein, whereas no synthesis was observed after addition of nigericin. Addition of K+, dicyclohexylcarbodiimide, carbonylcyanide p-trifluoromethoxyphenylhydrazone, or azide to the assay buffer inhibited ATP synthesis. Adenosine diphosphate and Mg2+ were found to be required. Ca2+, which can replace Mg2+ for the hydrolytic activity of the Mg2+-adenosine triphosphatase (ATPase) (EC 3.6.1.3), could not replace Mg2+ in the synthetic reaction and, in fact, inhibited ATP synthesis even in the presence of Mg2+. Strain NR-70, a mutant lacking the Mg2+-ATPase, was unable to synthesize ATP using an artificially imposed membrane potential. Additionally, the Mg2+-ATPase was found to contain tightly bound ATP.
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PMID:Adenosine 5'-triphosphate synthesis energized by an artificially imposed membrane potential in membrane vesicles of Escherichia coli. 0 30

(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

In sarcoplasmic reticulum of rabbit skeletal muscles the activity of Ca2+, Mg2+- dependent ATPase was distinctly inhibited under effect of neuroleptic drugs - derivatives of phenothiazine and butyrophenone. The effect of tricyclic antidepressants was less pronounced. Tranquilizers (derivatives of 1,4-benzodiazepine) inhibited the enzyme, but trioxazin was only slightly active. High concentrations of lithium salts and of psychostimulants caffeine and corasole were found to stimulate the Ca2+, Mg2+-ATPase activity; low concentrations of the substances slightly inhibited the enzyme. The blocking effect of psychotropic drugs was more distinct, if the enzyme preparations were previously treated with ATP.
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PMID:[Effect of psychotropic preparations on the activity of Ca- and Mg-dependent ATPase of the sarcoplasmic reticulum]. 1

Properties of HCO--3-stimulated ATPase from rat heart muscle nuclei were studied. The maximal activity of HCO--3-ATPase was observed at concentration of bicarbonate 25 mM. The enzyme had a pH optimum at pH 8.0-8.5. Bicarbonate stimulated the ATPase activity only in presence of Mg2+, Mn2+ and Zn2+, Co2+, Cd2+ and Ca2+ were ineffective. NaCO3 and Na2SO3 at concentration 30 mM stimulated the nuclear ATPase activity by 20% and 81%, respectively. Anions N3--, scn--, clO--4, and I-- inhibited both Mg2+-ATPase and HCO--3-ATPase. HSO--3 and SO2--4 ions did not affect the nuclear ATPase activity.
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PMID:[Anion-sensitive nuclear ATPase of the rat heart]. 2 54

The activity of ATPase was studied in highly purified rat liver and thymus cell nuclei, HCO3-, CO3(2-) and SO3(2-) stimulated nuclear ATPase in 1.5--2 times. HSO3- did not affect the enzyme activity, and NO3-, J-, ClO4-,F- and SCN- inhibited it. Bicarbonate increased V and decreased Ka for ATP. SCN- inhibited HCO3--ATPase activity non-competitively with respect to HCO3-. Mg2+-ATPase activity did not depend on pH, and HCO3-component of the activity was decreased under alkaline pH. Mg2+, Mn2+ and Co2+ increased the initial ATPase activity and helped its stimulation with HCO3-. Ba2+, Ni2+ and Zn2+ inhibited the ATPase activity, and Ca2+ did not affect it, Nuclear ATPase is sensitive to 2,4-dinitrophenol and DNAase. It is suggested that cell nuclei have their own H+-ATPase differing for some characteristics from mitochondrial H+-ATPase.
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PMID:[Investigation of adenosinetriphosphatase activity of rat liver and thymus cell nuclei]. 3 23

Growth of Clostridium perfringens was inhibited by compounds which dissipate or prevent the formation of electrochemical proton gradients. Membrane vesicles prepared from this organism exhibited Mg2+-dependent adenosine triphosphatase (ATPase) activity sensitive to N,N'-dicyclohexylcarbodiimide. Mg2+-ATPase activity was optimal of 50 degrees C, but no discrete pH optimum was observed. Adenosine triphosphate-dependent quenching of the fluorescence of the weak base quinacrine by everted membrane vesicles suggested that the Mg2+-ATPase is a proton pump capable of generating an electrochemical proton gradient. Adenosine triphosphate-dependent transport of Ca2+ by everted vesicles was sensitive to uncouplers and inhibitors of the Mg2+-ATPase.
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PMID:Properties and function of the proton-translocating adenosine triphosphatase of Clostridium perfringens. 4 Sep 63

The sodium-potassium activated adenosine triphosphatase (NaKATPase) activity of the rat cornea was investigated histochemically using a Pb2+-precipitation technique in which adenosine triphosphate (ATP) is used as substrate and two methods for potassium-dependent para-nitrophenyl-phosphatase (K-NPPase) activity. With all the three techniques used it was demonstrated that the sodium-potassium-activated adenosine triphosphatase (NaK-ATPase) activity is localized in the cell membranes of the endothelium whereas a much weaker activity was observed in the epithelium. When the Pb2+-technique was used, the epithelial cell membranes showed a weaker reaction in the presence of ouabain. This activity was only Mg2+-dependent and was presumably due to an Mg2+-dependent ATPase. The validity of the histochemical techniques for NaK-ATPase activity is discussed. The results emphasize the importance of the endothelium as the main site of Na+ transport in the cornea. Small amounts of the enzyme are also present in the epithelium, which seems to be rich in Mg2+-ATPase. Provided that careful controls are performed, all the methods give consistent results in the cornea.
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PMID:Transport adenosine triphosphatase activity in the rat cornea. 6 3

A fibrillar protein complex, possessing ouabain-insensitive Ca2+-ATPase activity was isolated from human erythrocyte membranes by using a low ionic strength extraction procedure. Mg2+-ATPase activity was revealed upon addition of rabbit skeletal muscle actin, thus demonstrating the presence of a myosin-like protein in the crude extract of the erythrocyte membrane. Upon sodium dodecylsulfate gel electrophoresis, the extract showed mainly the doublet of subunit molecular weight bands of 230 000 and 210 000, and more than 10 faster moving bands. Gel filtration of the erythrocyte membrane extract on Sepharose 4B furnished 4 fractions. Fraction I, containing the doublet and 80 000, 60 000 and 46 000 subunit molecular weight bands was 5-fold purified with respect to Ca2+-ATPase activity, but was devoid of actin-activated Mg2+-ATPase activity. Fraction II, containing only the doublet, was devoid of Ca2+ and actin-activated Mg2+-ATPase activity. The 210 000 subunit molecular weight protein could be phosphorylated in the presence of Mg2+ in the crude extract and Fraction I but not in Fraction II.
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PMID:Actin-activated ATPase from human erythrocytes. 12 97

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


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