Characterization of the (Na+-K+)-ATPase from endometrial plasma membranes of immature mammals]

The (Na+-K+)-ATPase in plasma membrane from Mammiferous endometrium is characterized by the Mg/ATP ratio equal to one, and by a distinct affinity for Na+ (1.3 mM) and K+ (2 mM). The activity is maximum for pH 7.4-7.5 in presence of Mg++ 2mM and ATP 2 mM, Na+ 140 mM and K+ 10 mM.     

The (Na+ + K+)-ATPase activity in brain of Quaking mice.

The (Na+ 4 K+)- and Mg2+-dependent ATPase distribution in several brain areas has been investigated in Quaking mutant mice characterized by myelin deficiency. A marked decrease of (Na+ + K+)-ATPase activity has been found in limbic structures, hypothalamus and cerebellum. The Mg2+-dependent activity did not change. A possible involvement of the impairment of the (Na+ + K+)-ATPase activity in the seizure susceptibility of this mice is discussed.     

Postnatal decline of (Ca2+ + Mg2+)-activated membrane ATPase in cattle red cells.

Acitivity of membrane bound (Ca2+ + Mg2+)-stimulated ATPase, associated with Ca2+ outward transport, in calf red cells is high at birth and declines with a rate constant of 0.041 d-1 after the 3rd week. The decline parallels the disappearance of fetal hemoglobin.     

Selective antagonism by Mg2+ of amino acid-induced depolarization of spinal neurones.

In the isolated frog or rat spinal cord, low concentrations of Mg2+ (0.5-1.00 mM) markedly depress, in a substantially Ca2+-independent manner, ventral root depolarizations produced by dorsal root stimulation and by certain amino acids (e.g. N-methyl-D-aspartate and L-homocysteate) but do not depress depolarizations produced by other excitatory amino acids (e.g. kainate and quisqualate). L-Aspartate-induced depolarizations are more sensitive to Mg2+ then are L-glutamate-induced depolarizations.     

Mg2+-HCO 3 − -ATPase and carbonic anhydrase in rat intestinal mucosa

Cellular and Molecular Life Sciences - Mg2+-dependent and HCO 3 − -stimulated ATPase activity was highest in the brush border (microvilli) of rat duodenal mucosa compared with that of the...     

Mg2+-HCO-3-ATPase and carbonic anhydrase in rat intestinal mucosa

Mg2+-dependent and HCO-3-stimulated ATPase activity was highest in the brush border (microvilli) of rat duodenal mucosa compared with that of the other gastrointestinal mucosa. This ATPase may be useful to neutralize the gastric acid in the duodenal lumen. Carbonic anhydrase seems to accomplish a subsidiary role in the above reaction.     

Insulin-like effect of dichloroacetic acid on hexose transport in Swiss 3T3 cells

Hexose transport in Swiss 3T3 cells was increased by treatment with dichloroacetic acid as well as by treatment with insulin. Neither extra- nor intracellular Ca2+ was found to be involved in their stimulatory action. On the other hand, the removal of intracellular Mg2+ resulted in a loss of the stimulation. These results suggest that dichloroacetic acid stimulates the hexose transport in Mg2+-dependent manner, similar to that of insulin.     

Temperature acclimation of Mg2+Ca2+-myofibrillar ATPase from a cold-selective teleost, Salvelinus fontinalis: a compromise solution

Brook trout (Salvelinus fontinalis, Mitchill) were acclimated over 15 weeks to either +4 degrees C or +24 degrees C. The effects of temperature on myofibrillar Mg2+Ca2+-ATPase activities were investigated. In contrast to goldfish, temperature acclimation does not alter the kinetic properties of the brook trout myofibrillar ATPase. Activation energy (delta G not equal to) is lower and substrate turnover number is higher than values previously reported for cold-adapted stenotherms. Properties of brook trout ATPase appear to be a compromise enabling function across a broad temperature range. The different strategies of adapting to seasonal temperature variations are briefly discussed.     

Ionophoric activity of the antibiotic X.14547 A in the mitochondrial membrane

Release of Ca++, Mg++ and K+ by the carboxylic ionophore X-14547 A was studied in the mitochondrial membrane. A comparison was made with A.23187 ( Calcimycin ) and X.537 A (Lasalocid A) under the same experimental conditions. It was shown that in this test system X.14547 A is primarily a K+ carrier comparable with X.537 A.     

Inhibitors of phosphatidylinositol 3-kinase activity prevent cell cycle progression and induce apoptosis at the M/G1 transition in CHO cells

Phosphatidylinositol 3-kinase (PI3-kinase) activity has been implicated in regulating cell cycle progression at distinct points in the cell cycle by preventing cell cycle arrest or apoptosis. In this study, the role of PI3-kinase activity during the entire G1 phase of the ongoing cell cycle was studied in Chinese hamster ovary (CHO) cells synchronized by mitotic shake-off. We show that inhibition of PI3-kinase activity during and 2 h after mitosis inhibited cell cycle progression into S phase. In the presence of the PI3-kinase inhibitor wortmannin or LY294002, cells were arrested during early G1 phase, leading to the expression of the cleaved caspase-3, a central mediator of apoptosis. These results demonstrate that PI3-kinase activity is required for progression through the M/G1 phase. In the absence of PI3-kinase activity, cells are induced for apoptosis in this particular phase of the cell cycle. Received 7 September 2005; received after revision 26 October 2005; accepted 11 November 2005     

Mast cells stimulated by membrane-bound,but not soluble,steel factor are dependent on phospholipase C activation

The steel factor (SLF) and c-Kit growth factor/receptor pair are key molecules governing mast cell development and survival. SLF is expressed on stromal cells as a membrane-bound molecule (mSLF) which can be cleaved by proteases to release a soluble form (sSLF). We investigated the importance of phospholipase C (PLC) activation in mast cells stimulated by sSLF and mSLF. PLC antagonists U73122, neomycin sulfate and oleic acid inhibited mast cell thymidine incorporation stimulated by mSLF, but not by sSLF. These antagonists suppressed sSLF-induced Ca2+ transients but did not significantly interfere with c-Kit phosphorylation or PLC-gamma2 recruitment. p85, the regulatory subunit of phosphatidylinositol 3-kinase (PI3-kinase), was found to be efficiently recruited to c-Kit following stimulation by sSLF or mSLF. However PKB/Akt, a kinase activated by PI3-kinase products, was phosphorylated following sSLF stimulation, but not with mSLF. Taken together, these studies demonstrate the importance of PLC activation by mSLF in supporting mast cells.     

Suppression of mitogen- and antigen-induced lymphocyte proliferation by lanthanides

Lanthanide ions (Ln3+) inhibited the proliferative response of human lymphocytes to various polyclonal mitogens and the 'purified protein derivative' (PPD) of the tuberculin antigen. Of the four Ln3+ ions tested lanthanum (La3+) was the strongest inhibitor; erbium (Er3+) and lutetium (Lu3+) were only weakly active, while samarium (Sm3+) had intermediate potency. At a concentration of 1 mM, La3+ almost completely inhibited the uptake of [3H]-thymidine by lymphocytes exposed to mitogenic agents. Trypan blue exclusion tests confirmed that the La3+ ions were not toxic. These findings may bear upon the reported anti-inflammatory properties of the lanthanides.     

Experiments on the mechanism of the inhibition of mitochondrial Ca2+ transport by La3+ and ruthenium red

Summary The effects of La³⁺ and ruthenium red on the energy-linked uptake of Ca²⁺ mediated by a synthetic neutral Ca²⁺ ionophore have been investigated in rat liver mitochondria. The results indicate that unspecific surface charge effects do not play a major role in the mechanism of inhibition of mitochondrial Ca²⁺ transport by La³⁺ and ruthenium red.Acknowledgments. The authors are indebted to Prof. W. Simon, ETH Zurich, for having provided samples of the synthetic neutral Ca²⁺ ligand, and to M. Mattenberger for the valuable technical assistence. The work was supported by a grant of the Swiss Nationalfonds (grant No. 3.1720.75).     

Mg2+-ATPase defective mutant of Escherichia coli and thiamine transport.

Mg2+-ATPase deficient mutant of Escherichia coli showed an evident dependency of thiamine uptake on the oxidative metabolism of glucose, whereas the parent strain did not. In both cells, this uptake was completely inhibited by H+ conductors.     

On the role of divalent cations in the reaction mechanism of malic enzyme.

The kinetic order of addition of Mg2+ and L-malate to malic enzyme has been determined. Mg2+ is the first to bind, and probably acts as a link between the substrate and the active site.     

The role of distinct membrane components of the enzyme in the ouabain sensitivity of Na+/K+ ATPase]

Purified plasma membranes from a cell line derived from the murine plasmocytoma MOPC 173 exhibited a 50% inhibition of the Na+K+ ATPase by 120 muM ouabain. EDTA treatment of such membranes induced a drop in the ouabain concentration needed for 50% inhibition to 0.4 muM. Supernatants obtained after EDTA treatment were able to complement with Ca(++) + Mg++ the washed EDTA treated membranes which recover their original resistance.     

Inhibition of E coli ATPase activity by a troponin component, TN-I, and by mitochondrial ATPase inhibitor.

The enzymic activity of Mg2+- or Ca2+-stimulated ATPase from Escherichia coli was inhibited by one of the troponin components, TN-I, and by mitochondrial ATPase inhibitor (F1-inhibitor). The inhibitory ability of component TN-I against Mg2+-stimulated AtPase activity was lost after digestion of component TN-I with trypsin. The Mg2+-stimulated ATPase activity inhibited by component TN-I was completely restored by the addition of another troponin component TN-C.     

The Ca2+-transport ATPases in smooth muscle

Summary A calmodulin stimulated Ca²⁺-transport ATPase which has many of the characteristics of the erythrocyte type Ca²⁺-transport ATPase has been purified from smooth muscle. In particular, the effect of calmodulin on these transport enzymes is mimiced by partial proteolysis and antibodies against erythrocyte Ca²⁺-transport ATPase also bind to the smooth muscle (Ca²⁺+Mg²⁺)ATPase. A correlation between the distribution of the calmodulin stimulated (Ca²⁺+Mg²⁺)ATPase and (Na⁺+K⁺)ATPase activities in smooth muscle membranes separated by density gradient centrifugation suggests a plasmalemmal distribution of this (Ca²⁺+Mg²⁺)ATPase. A phosphoprotein intermediate in smooth muscle which strongly resembles the corresponding phosphoprotein in sarcoplasmic reticulum of skeletal muscle may indicate the presence in smooth muscle of a similar type of Ca²⁺-transport ATPase.     

Spermine protects protein kinase C from phospholipid-induced inactivation

Phosphatidylserine (PS), an activator of protein kinase C (PKC) in the assay of protein phosphorylation, inhibited this enzyme in a time-dependent manner following preincubation in the absence of Ca²⁺. The phospholipid-induced inactivation of kinase activity was dependent on the PS content and on the charge density of liposomes. This inactivation of PKC could be reduced, but not completely eliminated, by addition of Ca²⁺. In the present work the effect of a naturally occurring polyamine (spermine) on the PS-induced inactivation of PKC was investigated. The presence of spermine during preincubation without Ca²⁺ was effective in suppressing the PS-induced inactivation of PKC over the period (20 min) required for PS to inhibit the enzyme by 95%. PKC exists in two membrane-bound states: a reversible one which can be dissociated by Ca²⁺ chelators (membrane-associated form) and an irreversible one which is chelator-stable (membrane-inserted form). Gel filtration experiments on the PKC-PS complex formed in the presence of Ca²⁺ indicated that less insertion of enzyme into liposomes occurred in the presence of spermine and that the kinase activity of the reversibly membrane-associated PKC was protected from PS inactivation.