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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 bivalent (Mg2+, Ca2+, Sr2+) and monovalent (K+, Na+, NH4+) cations on the ATPase activity of subfragment 1 of myosin (SI) with a decreased Mg2+ content (EDTA-SI) were studied. Mg2+ activate the EDTA-SI ATPase, but only in the absence of other activating cations. K+, NH4+, a2+ and Sr2+ have a much stronger activating effect on EDTA-SI ATPase than on Mg-SI (SI enriched with Mg2+) ATPase. Monovalent cations inhibit Mg2+-ATPase and Ca2+-ATPase of EDTA-SI, while K+ and NH4+ activate Sr2+-ATPase of EDTA-SI. Based on experimental results and literary data, a hypothesis on the participation of the cations in the functioning of myosin ATPase was postulated. This hypothesis entails the existence of two closely interconnected cation-binding sites in the vicinity of the myosin active center (one for bivalent and one for monovalent cations); the ATPase activity of myosin is at any moment dependent on the nature of cations present in these two sites. An attempt to explain the role of the cations in the accomplishment of the ATPase reaction by myosin was made.
Biokhimiia 1980 Dec
PMID:[Role of bivalent and monovalent cations in the functioning of myosin ATPase]. 645 45

Magnesium-dependent adenosine triphosphatase (Mg2+-ATPase) activities wee studied in human neutrophilic polymorphonuclear leucocytes. Kinetic studies on whole leucocyte homogenates produced curvilinear kinetics suggesting the presence of at least two forms of Mg2+-ATPase. Neutrophils were homogenized in isotonic sucrose and, after low-speed centrifugation, the supernatant was subjected to analytical subcellular fractionation. Gradient fractions were assayed for Mg2+-ATPase and for principal organelle marker enzymes. Mg2+-ATPase was distributed between the plasma membrane, mitochondrial and cytosol fractions. Kinetic and inhibitor studies on Mg2+-ATPase from each localization indicated the presence of three forms of the enzyme. The plasma membrane and mitochondrial activities had a Km value of 0.2 mmol/l for ATP, whilst the Km for the cytosolic enzyme was 1.8 mmol/l. Inhibitor studies showed further differences between the three enzymes. Neutrophils were isolated from control subjects, patients with chronic granulocytic leukaemia and patients in the third trimester of pregnancy. The specific activities (mUnits/mg protein) of Mg2+-ATPase, in contrast to those of alkaline phosphatase, were similar in all three patient groups. This result, together with the fractionation experiments and inhibitor studies, strongly suggest that the ATPase is not attributable to neutrophil alkaline phosphatase.
Eur J Clin Invest 1980 Dec
PMID:Subcellular localization and properties of adenosine triphosphatase in human polymorphonuclear leucocytes. 645 79

The administration of single oral doses of 200 micrograms kg-1 of 2,3,7,8-tetrachlorodibenzo-p-dioxin to females of the outbred, Lac : P strain of rat results in the formation of hepatic multinucleate cells by cell fusion. Liver cell plasma membranes isolated 6 or 11 days after dosing show two distinct changes. The first is a decrease of the activity of K+-Mg2+-ATPase, which confirms histochemical observations. The second is the formation, in those animals showing a more severe intoxication, of a population of plasma membranes which are less dense than usual and which consist of extended membrane sheets. It is suggested that these alterations are consequent on a disturbance of lipid metabolism in the hepatic cells and that they represent early manifestations of the toxic process which leads to the formation of multinucleate cells.
J Appl Toxicol 1981 Dec
PMID:Biochemical and morphological changes induced by 2,3,7,8-tetrachlorodibenzo-p-dioxin in the rat liver cell plasma membrane. 718 97

A rapid isolation method was developed for plasma membranes from mouse lymphoid cells such as lymph node lymphocytes, thymocytes, radiation-induced thymoma cells and L1210 cells. Lysates of these lymphoid cells were prepared by Dounce homogenization under hypotonic conditions and directly layered on sucrose step density gradients containing 2 mM CaCl2 and 5 mM MgCl2, and centrifuged at 52 000 X g for 1 h. Plasma membrane fractions appeared at the interface between 20 and 42% sucrose in the gradients. The procedure permitted purified membranes from cells to be obtained within 3 h, and the preparations appeared to be uniform by electron microscopy. Specific activities of (Na+ + K+)-ATPase, Mg2+-ATPase and 5'-nucleotidase of the isolated plasma membranes were enriched 23- to 61-fold, 12- to 15-fold and 18- to 34-fold, respectively, in comparison with those of the corresponding cell homogenates. Cholesterol content of the malignant cell membranes was lower than that of the normal membranes and the molar ratio of cholesterol to phospholipid of the malignant cell membranes was also lower than that of the normal membranes. A decreased plasmalogen content was observed in the malignant plasma membranes, together with a higher percentage of phosphatidylethanolamine and a lower percentage of phosphatidylserine. In the normal cell membranes, thymocytes contained a higher percentage of phosphatidylcholine and a lower percentage of sphingomyelin than those of the lymph node lymphocytes. At all temperature ranges (5 to 40 degrees C) the plasma membranes of the malignant cells had lower microviscosity than those of the normal cells.
Biochim Biophys Acta 1981 Dec 07
PMID:Rapid isolation and lipid characterization of plasma membranes from normal and malignant lymphoid cells of mouse. 731 6

The heavy chain of myosin-ID isolated from Dictyostelium was identified as an in vitro substrate for members of the Ste20p family of serine/threonine protein kinases which are thought to regulate conserved mitogen-activated protein kinase pathways. Yeast Ste20p and Cla4p and mammalian p21-activated protein kinase (PAK) phosphorylated the heavy chain to 0.5-0.6 mol of Pi/mol and stimulated the actin-dependent Mg2+-ATPase activity to an extent equivalent to that of the Ste20p-like myosin-I heavy chain kinase isolated from Dictyostelium. PAK purified from rat brain required GTPgammaS-Cdc42 to express full activity, whereas recombinant mouse mPAK3 fused to glutathione S-transferase and purified from bacteria, and Ste20p and Cla4p purified from yeast extracts were fully active without GTPgammaS-Cdc42. These results suggest, together with the high degree of structural and functional conservation of Ste20p family members and myosin-I isoforms, that myosin-I activation by Ste20p family protein kinases may contribute to the regulation of morphogenetic processes in organisms ranging from yeast to mammalian cells.
J Biol Chem 1996 Dec 13
PMID:Activation of myosin-I by members of the Ste20p protein kinase family. 894 16

In contrast to the F1-ATPases from bovine mitochondria and the thermophilic Bacillus PS3, which are reversibly inhibited by dequalinium in the absence of irradiation, the Mg2+-ATPase activity of heat- or dithiothreitol-activated chloroplast F1 (CF1) from spinach chloroplasts is slightly stimulated by dequalinium. Conversely, dequalinium is a partial inhibitor (maximal inhibition is 85-90%) of the Ca2+-ATPase of CF1 activated by heat, dithiothreitol, or octylglucoside. The Mg2+- and Ca2+-ATPase activities of CF1 respond differently in the presence of lauryl dimethylamine oxide (LDAO) in the assay medium. Whereas the Mg2+-ATPase activity of heat- or dithiothreitol-activated CF1 is stimulated up to 14-fold by increasing concentrations of LDAO, the Ca2+-ATPase is inhibited in a biphasic manner by increasing concentrations of LDAO. In the presence of LDAO, dequalinium does not stimulate the heat-activated Mg2+-ATPase over that promoted by LDAO alone. That dequalinium slightly stimulates Mg2+-ATPase activity although it inhibits Ca2+-ATPase activity can be reconciled by assuming that dequalinium binds to two sites in CF1, a stimulatory site that also binds LDAO and an inhibitory site. By acting as a partial inhibitor of the Mg2+-ATPase activity that it activates, the combined effect of dequalinium is modest stimulation. Irradiation of heat- or dithiothreitol-activated CF1 or the alpha3beta3gamma subcomplex of CF1 in the presence of 12 microM dequalinium led to rapid photoinactivation. ATP and ADP, separately or in combination with Mg2+, protect against photoinactivation. After photoinactivating the alpha3beta3gamma subcomplex of CF1 with [14C]dequalinium, tryptic and peptic digests of the isolated, derivatized beta subunit were fractionated by high performance liquid chromatography. Sequencing of the isolated, radioactive tryptic and peptic peptides revealed that Metbeta183, which is at or near the catalytic site, is derivatized in a single beta subunit when CF1 is photoinactivated with [14C]dequalinium.
J Biol Chem 1997 Dec 19
PMID:Photoinactivation of the F1-ATPase from spinach chloroplasts by dequalinium is accompanied by derivatization of methionine beta183. 940 35

Pgp is an atypical translocating ATPase, with low affinity for ATP and high constitutive ATPase activity. Pgp also has an unusually broad specificity for hydrophobic substrates, including many chemotherapeutic drugs. Transport studies in reconstituted systems indicate that drug transport requires ATP hydrolysis and is active, generating a drug concentration gradient. Binding of drugs and ATP to Pgp induces conformational changes in the protein, and the drug binding site is conformationally coupled to the NBDs. Evidence accumulated to date suggests that the transporter interacts directly with nonpolar substrates within the membrane environment, and may act as a drug flippase, moving drugs from the inner to the outer leaflet of the bilayer. Chemosensitizers that block the action of Pgp are proposed to act as alternative substrates, but their high rate of spontaneous flip-flop across the membrane results in futile cycling of the transporter.
J Membr Biol 1997 Dec 01
PMID:The P-glycoprotein efflux pump: how does it transport drugs? 978 87

We studied the effect of cyclosporine A on hepatic Ca2+, Mg2+-ATPase and F-actin on bile canalicular and basolateral membranes in rats fed either soyabean lecithin, or triacylglycerol enriched diet, or low fat diet. Ca2+, Mg2+-ATPase histochemical activity was not modified in lecithin-cyclosporine A group, whereas the activity was decreased in the other groups. The triacylglycerol-cyclosporine A group had the lower activity. The histochemical staining of F-actin was quite normal in lecithin-cyclosporine group but decreased in the other cyclosporine A treated groups. The lower staining was observed in the triacylglycerol-cyclosporine group. The alteration of Ca2+, Mg2+-ATPase and F-actin by cyclosporine A, related to cholestasis evidenced by a decrease in bile salt secretion, were prevented by dietary soyabean lecithin and amplified by dietary soyabean triacylglycerol.
Cell Mol Biol (Noisy-le-grand) 1998 Dec
PMID:Modification of Ca2+, Mg2+-ATPase and F-actin distribution in hepatocytes of cyclosporine A treated rats. Effect of soyabean lecithin and triacylglycerol. 987 9

B16 murine melanoma melanosomes were purified using sucrose density gradient centrifugation. ATPase activity was evaluated in presence of specific ATPase inhibitors, and compared with melanosome ATP-driven proton translocating activity in the melanosome. Mg2+ dependent ATPase activity was greatly inhibited (82%) by the specific inhibitors of vaculor proton translocating ATPase; Cis-didimethylsulfoxide dichloroplatinum (II) at approximately 90 microM and bafilomycin AI at two fold higher concentrations. Less inhibition, about 30 and 45% was obtained with N, N1-dicyclohexylcarbodiimide and N-ethylmaleimide, and the maximal effect occurred in the 50-100 microM and 0.1-1.5 mM ranges, respectively. These drugs at similar concentrations also inhibited the proton pumping activity to the same extent as observed for ATPase activity and half-maximal inhibition of each activity was found at nearly similar concentrations. Carbonylcyanide p-trifluoromethoxyphenyl hydra zone (FCCP) prevented ATP from setting up a pH gradient across the melanosomal membrane but stimulated Mg2+ ATPase activity significantly. Replacement of 5 mM Mg2+ with equimolar Ca2+ brought about a 60% inhibition in divalent cation-dependent ATPase- activity, and an 85% inactivation of ATP-linked melanosomal H+ pump activity. In the presence of optimal concentrations of Ca2+ and Mg2+ ATPase activity was similar to that seen in a Mg2+ medium. In Ca2+ medium ATPase activity was inhibited by CDDP and stimulated by FCCP, however these effects were two to three fold less than those observed in Mg2+ medium. FCCP failed to stimulate ATPase activity in CDDP- supplemented medium, thus suggesting that the same ATPase activity fraction was sensitive to both CDDP and FCCP. Mg2+-ATPase activity, like the proton-pump was anion dependent. The lowest activity was recorded in F medium, and increased in the order of F < So4(2-) < CL- = Br-. These results show that the ATPase activity may be related to the melanosomal proton pump.
Mol Cell Biochem 1998 Dec
PMID:Characterization of Mg2+-ATPase activity in isolated B16 murine melanoma melanosomes. 987 59

Vectorial sorting of plasma membrane protein-containing vesicles is essential for the establishment and maintenance of cell polarity. In the present study, the involvement of altered vesicle transport in the redistribution of membrane-bound Ca2+, Mg2+-ATPase resulting from cholestasis was investigated in hepatocytes. Cholestasis was induced in rat liver by common bile duct ligation. Ca2+, Mg2+-ATPase activity was demonstrated histochemically at the light and electron microscopical levels. Microtubules, an important factor for transcellular transport of vesicles, were studied in situ by immunofluorescence microscopy and electron microscopy in detergent-extracted preparations. The results showed that microtubules underwent significant changes after common bile duct ligation. The most pronounced alteration was focal accumulation of beta-tubulin in the cytoplasm of hepatocytes after 7 days of common bile duct ligation. At the electron microscopical level, the number of microtubules was increased considerably. In control livers, the activity of Ca2+, Mg2+-ATPase was localized only at the apical plasma membrane of hepatocytes, but it was also present at the basolateral plasma membrane after common bile duct ligation. The number of intracellular vesicles containing Ca2+, Mg2+-ATPase activity was increased strikingly, and some of them were associated with lateral membrane domains in which Ca2+, Mg2+-ATPase activity was found. It is concluded that common bile duct ligation induces the rearrangement of microtubules, which may disturb vectorial transport of Ca2+, Mg2+-ATPase-containing vesicles in hepatocytes, leading to the redistribution of Ca2+, Mg2+-ATPase.
Histochem J 1998 Dec
PMID:The involvement of altered vesicle transport in redistribution of Ca2+, Mg2+-ATPase in cholestatic rat liver. 1010 Jul 33


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