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)

The activities of Mg2+-ATPase (Mg2+-activated ATPase), (Ca2+ + Mg2+)-activated ATPase and (Na+ + K+)-activated ATPase have been determined in microsomes (microsomal fractions) obtained from rat myometrium under different hormonal conditions. Animals were either ovariectomized and treated for a prolonged period of time with 17 beta-oestradiol or progesterone, or myometria were obtained at day 21 of pregnancy. In each case the endometrium was carefully removed. The Mg2+-ATPase consists of two components: an inactivating labile component and a second constant component. The rate of ATP hydrolysis by the labile component of the Mg2+-ATPase declines exponentially as a function of time after adding the membranes to the assay medium; this inactivation is caused by the presence of ATP in the medium. This ATPase activity inhibited by ATP is catalysed by a labile enzyme and hence it gradually diminishes within a few hours, even when the microsomes are kept on ice. This labile component has the highest activity in microsomes from pregnant rats, a lower activity in progesterone-treated rats, and the lowest in 17 beta-oestradiol-treated rats. This component of the Mg2+-ATPase is not affected by 90 nM-oxytocin. The constant component of the Mg2+-ATPase must be ascribed to a different enzyme, which, in contrast with the labile component, is very stable and not affected by the hormonal status of the animal. This constant component of the Mg2+-ATPase is inhibited both by Ca2+-calmodulin, and by oxytocin in microsomes from pregnant and from progesterone-treated animals, whereas such inhibition does not occur in microsomes from 17 beta-oestradiol-treated animals. The activity of the (Na+ + K+)-activated ATPase is not dependent on the hormonal status of the animal. Myometrial microsomes present an ATP-dependent Ca2+ transport, irrespective of the hormonal condition, but only in microsomes obtained from rats treated with 17 beta-oestradiol, can a (Ca2+ + Mg2+)-activated ATPase activity be demonstrated. This activity can be stimulated by calmodulin.
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PMID:Effect of ovarian steroids on membrane ATPase activities in microsomes (microsomal fractions) from rat myometrium. Inhibition of a component of the Mg2+-activated ATPase by Ca2+-calmodulin and by oxytocin. 283 47

The apparent Mg2+-activated ATPase activity measured by the continuous NADH-coupled enzyme assay was studied in a number of microsomal preparations obtained from smooth muscle of the myometrium from pregnant or 17 beta-oestradiol-pretreated rats, the bovine aorta, the guinea-pig taenia coli, the rabbit ear artery and pig antrum. It was shown that this ATPase assay is prone to the effects of a number of artefacts that are tissue-dependent. The apparent Mg2+-ATPase activity in microsomes (microsomal fractions) from myometrium, aorta and taenia coli declines non-linearly during the assay. Its initial high rate gradually diminishes over 15-60 min, depending on the type of smooth muscle, to a constant value. This decline depends on the presence of ATP and can be partially prevented by concanavalin A. The non-linearity is limited in microsomes from rabbit ear artery. In microsomes from antrum the apparent Mg2+-ATPase activity actually increases with time, albeit gradually. Storage on ice of the microsomes of the aorta, and especially of myometrium of pregnant rats and of taenia coli, is accompanied over a few hours after their preparation by a gradual suppression of the component of the Mg2+-ATPase activity that is inhibited by ATP. The Mg2+-ATPase activity in microsomes from antrum remains constant. NADH oxidase activity accounts for 10% of the Mg2+-ATPase activity in microsomes from stomach smooth muscle. The apparent initial non-linearity of the Mg2+-ATPase activity in that tissue is due to a time-dependent decrease of a rotenone-sensitive NADH oxidase activity. The adenylate kinase activity, as deduced from the effect of the adenylate kinase inhibitor P1,P5-di(adenosine-5') pentaphosphate, could account for 45.0, 35.0 and 31.0% respectively of the Mg2+-ATPase activity in microsomes from stomach, myometrium and aorta. No adenylate kinase activity could be detected in microsomes from ear artery and taenia coli. When microsomes from stomach smooth muscle were separated on a sucrose gradient, the contribution of adenylate kinase and NADH oxidase to the Mg2+-ATPase activity was most pronounced in the higher-density fractions. Part of the NADH oxidase activity and of the Mg2+-ATPase activity, and most of the adenylate kinase activity, are not sedimented at 224000 gmax. for 30 min and may therefore be present as soluble enzymes.(ABSTRACT TRUNCATED AT 400 WORDS)
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PMID:Characterization of the Mg2+-activated ATPase activity in smooth-muscle membranes. NADH oxidase and adenylate kinase interfere with the NADH-coupled enzyme assay. 283 48

Sodium-potassium adenosinetriphosphatase (Na+-K+-ATPase) is modulated by functional demands. We determine whether Na+-K+-ATPase specific activity was changed by oral administration of different bile salts and whether upregulation in the liver is due to increased numbers of catalytic units. In rats after bile duct drainage for 18 h, Na+-K+-ATPase activity was reduced to 50% of control in liver and ileum but unchanged in jejunum and kidney. Increased Na+-K+-ATPase activity after short-term feeding of bile salts was noted only following trihydroxy bile salts, i.e., taurocholate (100 mg/100 g body wt) increased hepatic Na+-K+-ATPase 143% and ileum 138% above control, whereas jejunum and kidney were unchanged. Chronic feeding of trihydroxy bile salts for 4 days increased hepatic Na+-K+-ATPase (214-260%) and alkaline phosphatase (189-274%), whereas 5'-nucleotidase and Mg2+-ATPase activities were unchanged from control. Plasma membrane Na+-K+-ATPase activity significantly increased as early as 4 h after taurocholate administration, whereas homogenate activity did not rise until 16 h; both reached a new steady state between 24 and 48 h. Sixteen hours after bile salt feeding, increased Na+-K+-ATPase activity was blocked by cycloheximide, and in the liver increased enzyme activity (179%) was associated with a comparable change in sodium-dependent [gamma-32P]ATP binding (162%) to liver plasma membrane fractions. These studies show Na+-K+-ATPase activity adapts selectively in liver and ileum following administration of trihydroxy bile salts, and the process involves increased density of Na+-K+ pump sites on the liver plasma membrane.
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PMID:Selective modulation of hepatic and ileal Na+-K+-ATPase by bile salts in the rat. 283 64

Upon tryptic digestion of synaptosomes, ATPase activities decreased in the order of Cl(-)-ATPase greater than or equal to Na+,K+-ATPase greater than anion-insensitive Mg2+-ATPase. Upon synaptosome treatment with hypotonic solution, Cl(-)-ATPase or anion-insensitive Mg2+-ATPase was slightly inactivated, while Na+,K+-ATPase underwent a much larger degree of inactivation. ATP-Mg inhibited the ATPase digestion in the hypotonic-solution-treated synaptosomes in a concentration-dependent manner, but not in the untreated synaptosomes. These results suggest that trypsin-digestible site of Cl(-)-ATPase are present on both sides of the synaptosomal plasma membrane, and the ATP-Mg binding site of the enzyme is located on the inner surface of the membrane.
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PMID:Proteolytic digestion of Cl(-)-ATPase in rat brain synaptosomes. 283 80

Caldesmon, an actin- and calmodulin-binding protein of smooth muscle, is a protein serine/threonine kinase capable of Ca2+/calmodulin-dependent autophosphorylation [Scott-Woo & Walsh (1988) Biochem. J. 252, 463-472]. Phosphorylation nullifies the inhibitory effect of caldesmon on the actin-activated Mg2+-ATPase activity of smooth-muscle myosin [Ngai & Walsh (1987) Biochem. J. 244, 417-425]. We have characterized the kinase activity of caldesmon of chicken gizzard smooth muscle. Autophosphorylation requires Ca2+/calmodulin, but is unaffected by other second messengers (Ca2+/phospholipid/diacylglycerol, cyclic AMP or cyclic GMP), and is inhibited by the calmodulin antagonists chlorpromazine and compound 48/80, with 50% inhibition at 39.8 microM and 12.0 ng/ml respectively. Half-maximal activation of autophosphorylation occurs at 60-80 nM-Ca2+ and 0.14 microM-calmodulin, and maximal activity at 0.14-0.18 microM-Ca2+ and 1 microM-calmodulin; activation is gradually lost at higher Ca2+ and calmodulin concentrations. Autophosphorylation is pH-dependent, with maximal activity over the range pH 7-9, and requires free Mg2+ in addition to the MgATP2- substrate. The Km for ATP is 15.6 +/- 4.1 microM (mean +/- S.D., n = 4), and kinase activity is inhibited by increasing ionic strength [half-maximal inhibition at I = 0.094 +/- 0.009 M (mean +/- S.D., n = 4)]. Autophosphorylation does not affect the rate of hydrolysis of caldesmon (free or bound to calmodulin) by alpha-chymotrypsin. However, a slight difference in peptides generated from phospho- and dephospho-forms of caldesmon is observed. The binding of phospho- or dephospho-caldesmon to F-actin protects the protein against chymotryptic digestion, but does not alter the pattern of peptide generation. Characterization of proteolytic fragments of caldesmon generated by alpha-chymotrypsin and Staphylococcus aureus V8 protease enables localization of the phosphorylation sites and the kinase active site within the caldesmon molecule.
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PMID:Characterization of the autophosphorylation of chicken gizzard caldesmon. 285 Jul 99

H+-translocating, Mg2+-ATPase was solubilized from vacuolar membranes of Saccharomyces cerevisiae with the zwitterionic detergent N-tetradecyl-N,N-dimethyl-3-ammonio-1-propanesulfonate and purified by glycerol density gradient centrifugation. Partially purified vacuolar membrane H+-ATPase, which had a specific activity of 18 units/mg of protein, was separated almost completely from acid phosphatase and alkaline phosphatase. The purified enzyme required phospholipids for maximal activity and hydrolyzed ATP, GTP, UTP, and CTP, with this order of preference. Its Km value for Mg2+-ATP was determined to be 0.21 mM and its optimal pH was 6.9. ADP inhibited the enzyme activity competitively, with a Ki value of 0.31 mM. The activity of purified ATPase was strongly inhibited by N,N'-dicyclohexylcarbodiimide, 1-ethyl-3-(3-dimethylaminopropyl)carbodiimide, tributyltin, 7-chloro-4-nitrobenzoxazole, diethylstilbestrol, and quercetin, but was not affected by oligomycin, sodium azide, sodium vanadate, or miconazole. It was not inhibited at all by antiserum against mitochondrial F1-ATPase or mitochondrial F1-ATPase inhibitor protein. These results indicated that vacuolar membrane H+-ATPase is different from either yeast plasma membrane H+-ATPase or mitochondrial F1-ATPase. The vacuolar membrane H+-ATPase was found to be composed of two major polypeptides a and b of Mr = 89,000 and 64,000, respectively, and a N,N'-dicyclohexylcarbodiimide binding polypeptide c of Mr = 19,500, whose polypeptide composition was also different from those of either plasma membrane H+-ATPase or mitochondrial F1-ATPase of S. cerevisiae.
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PMID:Purification and properties of H+-translocating, Mg2+-adenosine triphosphatase from vacuolar membranes of Saccharomyces cerevisiae. 285 69

The ATP-dependent Ca2+ uptake by and the Ca2+-Mg2+-activated ATPase activity in the subcellular fractions from the eggshell gland of two varieties of ducks, Indian Runner ducks (IRD) and the cross-breed of Swedish and Rouen ducks (SRD), showed functional changes during eggshell formation in relation to the values in the resting state. DDE inhibited the Ca2+ uptake (Ca) but increased the Ca2+-Mg2+-ATPase activity (P) of fractions from active but not of those from resting glands. DDE reduced the Ca/P ratio of several fractions from active glands. DDE inhibited the functional increase in Ca2+-Mg2+-ATPase in the IRD homogenate, however. The effect of DDE on the eggshell index of mature eggshell was greater in IRD than in SRD, the reason for this being that the effect was exerted during a shorter time period in the latter variety.
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PMID:Relation between Ca metabolism and ATPase activities in the subcellular fractions from duck eggshell gland mucosa after DDE administration during different stages of eggshell formation. 286 48

Diethylstilbestrol (DES) was found to inhibit reversibly the hydrolysis of MgATP (80% at 100 microM) and proton pump activity (I50 approximately equal to 15 microM, complete at 100 microM) in chromaffin granule ghosts. The parallel inhibition suggests a tight kinetic coupling between the two activities. The Mg2+-ATPase activity, but not proton pumping, was partially restored by N,N'-dicyclohexylcarbodiimide, indicating that the two inhibitors in combination cause a partial uncoupling. The non-competitive type of inhibition shows that the action of DES is distal to the site of ATP binding and hydrolysis. Although unspecific, the interaction of DES with the chromaffin granule membrane seems primarily to affect the H+-ATPase.
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PMID:Inhibition of the H+-ATPase in bovine adrenal chromaffin granule ghosts by diethylstilbestrol. Evidence for a tight coupling between ATP hydrolysis and proton translocation. 289 26

Isolation of F1-ATPase from Rhodospirillum rubrum by chloroform extraction of chromatophores, followed by purification on a glycerol gradient, results in a very pure enzyme preparation containing five subunits with high Ca2+-ATPase activity (15 mumol per min per mg protein). Furthermore, conditions are reported under which the purified F1 exhibits Mg2+-dependent ATPase activity of about 35 mumol per min per mg protein. NaHCO3 stimulates the Mg2+-activity from 1.5 mumol per min per mg protein to 5 mumol per min per mg protein giving a maximal activity at a concentration of about 60 mM NaHCO3. Lauryl dimethylamine oxide (LDAO), octyl glucoside and nonanoyl N-methylglucamide enhance the Mg2+-ATPase activity from 1.5 to 14, 22 and 35 mumol per min per mg protein, respectively, in the absence of NaHCO3, and from 5 to 34, 30 and 37 mumol per min per mg protein, respectively, in the presence of 50 mM NaHCO3. The Vmax is increased, but the Km for ATP remains the same, about 0.22 mM, both in the absence of activators and in the presence of NaHCO3, LDAO or NaHCO3 plus LDAO. Ca2+-dependent ATPase activity is slightly stimulated by NaHCO3 but strongly inhibited by octyl glucoside.
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PMID:Conversion of coupling factor 1 of Rhodospirillum rubrum from a Ca2+-ATPase into a Mg2+-ATPase. 290 Dec 72

The hydrophobic compound diethylstilbestrol inhibits the generation of the proton gradient and the membrane potential in chromatophores from Rhodospirillum rubum and dissipates proton gradients over asolectin vesicle membranes. The Ca2+-ATPase activity of chromatophores, of purified F0F1-ATPase and of purified F1-ATPase is also decreased in the presence of diethylstilbestrol. Other repressed activities are the pyrophosphatase activity of soluble pyrophosphatase from yeast and the NADH oxidation by L-lactate:NAD oxidoreductase. We have previously reported that also ATP synthesis, PPi synthesis and PPi hydrolysis of R. rubrum chromatophores are inhibited by diethylstilbestrol [Strid et al. (1987) Biochim. Biophys. Acta 892, 236-244]. Addition of bovine serum albumin reverses or prevents diethylstilbestrol-induced inhibition of the activities tested. On the other hand, the Mg2+-ATPase activity of chromatophores, purified F0F1-ATPase and purified F1-ATPase are stimulated by low concentrations of diethylstilbestrol. On the basis of its hydrophobicity and the reversal of its inhibition by bovine serum albumin, diethylstilbestrol is proposed to act unspecifically on membranes and at hydrophobic domains of proteins. Such an attack upon the subunits of the F1-ATPase, altering the subunit interactions, is proposed to explain the different results obtained for the Ca2+-ATPase and the Mg2+-ATPase.
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PMID:Diethylstilbestrol. Interactions with membranes and proteins and the different effects upon Ca2+- and Mg2+-dependent activities of the F1-ATPase from Rhodospirillum rubrum. 290 53


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