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.     

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.     

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.     

The site of action of La3+ in the reaction cycle of the human red cell membrane Ca2+-pump ATPase

Lanthanum (La3+) inhibits the Ca-pump of the red cell by arresting the protein in a phosphorylated form (PI). Similar La3+ concentrations are required to increase the amount of PI and to stop PI-decay. In the presence of La3+ phosphorylation becomes insensitive to Mg2+. PI made in the presence of Mg2+ is not prevented from decaying by subsequent addition of La3+, whereas that made in the absence of Mg2+ is. Taken together, these findings seem to indicate that La3+ blocks the transition between a 1st and a 2nd form of PI.     

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 (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.     

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.     

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.     

Influence of ethanol on calcium, inositol phospholipids and intracellular signalling mechanisms

Studies have implicated Ca++ in the actions of ethanol at many biochemical levels. Calcium as a major intracellular messenger in the central nervous system is involved in many processes, including protein phosphorylation enzyme activation and secretion of hormones and neurotransmitters. The control of intracellular calcium, therefore, represents a major step by which neuronal cells regulate their activities. The present review focuses on three primary areas which influence intracellular calcium levels; voltage-dependent Ca++ channels, receptor-mediated inositol phospholipid hydrolysis, and Ca++/Mg++-ATPase, the high affinity membrane Ca++ pump. Current research suggests that a subtype of the voltage-dependent Ca++ channel, the dihydropyridine-sensitive Ca++ channel, is uniquely sensitive to acute and chronic ethanol treatment. Acute exposure inhibits, while chronic ethanol exposure increases 45Ca++-influx and [3H]dihydropyridine receptor binding sites. In addition, acute and chronic exposure to ethanol inhibits, then increases Ca++/Mg++-ATPase activity in neuronal membranes. Changes in Ca++ channel and Ca++/Mg++-ATPase activity following chronic ethanol may occur as an adaptation process to increase Ca++ availability for intracellular processes. Since receptor-dependent inositol phospholipid hydrolysis is enhanced after chronic ethanol treatment, subsequent activation of protein kinase-C may also be involved in the adaptation process and may indicate increased coupling for receptor-dependent changes in Ca++/Mg++-ATPase activity. The increased sensitivity of three Ca++-dependent processes suggest that adaptation to chronic ethanol exposure may involve coupling of one or more of these processes to receptor-mediated events.     

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.     

Effect of free fatty acids and cholesterol in vitro on liver plasma membrane-bound enzymes

The effect of cholesterol and fatty acid treatment in vitro was tested on rat liver plasma membrane-bound enzymes and lipid fluidity. The observed alterations of membrane fluidity affect both (Na+-K+)-ATPase and Mg2+-ATPase activities but not 5'-nucleotidase; basal adenylate cyclase as well as its hormonal sensitivity were differentially affected by changes of membrane microenvironment.     

Dissociation-constants of metat-ion-complexes with alkaline phosphatase from pig kidney.

Using metal-ion buffers it was possible to remove Zn2+, Mg2+ and Mn2+ ions of pig kidney alkaline phosphatase reversibly. The dissociation constants obtained are KEMg: 4 X 10(-7) M, KEMn: 4 X 10(-8) M and KEZn: 8 X 10(-13) M (22 degrees C, pH: 9.6, mu: 0.07).     

Further support for the postsynaptic action of substance P and its blockade with baclofen in neurons of the guinea-pig hypothalamus in vitro

Effects of substance P on neurons of the guinea-pig hypothalamus in vitro and antagonism between substance P and baclofen were investigated. Substance P increased the firing rate of neurons in the medium containing 0 mM Ca2+ and 12 mM Mg2+. The excitatory action of substance P was antagonized by a low dose of baclofen whereas that of acetylcholine was not antagonized even by much higher doses of baclofen.     

Effect of heat treatment on the ATPase activity of various sarcoplasmic reticulum preparations.

Ca2+-stimulated ATPase activity of sarcoplasmic reticulum (SR) preparations is activated after a short period of preincubation at temperatures between 40 and 45 degrees C, but for temperatures higher than 48 degrees C pronounced denaturation is observed. Heat denaturation is decreased if Mg2+ or K+ are present during heat treatment.     

Activation and specificity of alkaline phosphatase of a mineralizing collagen-rich system

Summary Alkaline phosphatase from tibia tendon ofMeleagris gallopavo L. was highly purified. The enzyme activation by different ions was measured. Mg²⁺ showed a high activation with a broader spectrum of phosphomonoester hydrolization. The in vivo Mg²⁺ concentration was an optimum for in vitro activation.Dedicated to Prof. Dr. G. Pfefferkorn on the occasion of his 65^th birthday.We thank Deutsche Forschungsgemeinschaft for support.     

Insulin effect in vitro on human erythrocyte plasma membrane

The effect of porcine insulin has been tested in vitro on human erythrocyte plasma membrane (Na+-K+) and Mg2+-ATPase activities as well as on membrane fluidity. The results indicate that the hormonal treatment significantly inhibits (Na+-K+)-ATPase activity, and at the same time decreases membrane fluidity.     

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...     

Demonstration and characterization of mannosyl phosphoryl dolichol synthesized in the outer membrane of liver mitochondria]

There is in mitochondrial outer membrane a mannosyl-transferase which is able to catalyse the mannose transfer on a polyprenic acceptor, to give a mannosyl-phosphoryl-dolichol. This enzyme is stimulated by Mn2+, Mg2+ and dithiothreitol. It is inhibited by GDP, mersalyl and EGTA.     

ERK activation by Ca2+ ionophores depends on Ca2+ entry in lymphocytes but not in platelets, and does not conduct membrane scrambling

Rapid Ca²⁺-dependent phospholipid (PL) reorganization (scrambling) at the plasma membrane is a mechanism common to hematopoietic cells exposing procoagulant phosphatidylserine (PS). The aim of this research was to determine whether activation of the extracellular signal-regulated kinase (ERK) pathway was required for PL scrambling, based on a single report analyzing both responses induced by Ca²⁺ ionophores in megakaryoblastic HEL cells. Ca²⁺ ionophore-stimulated ERK phosphorylation was induced in platelets without external Ca²⁺, whereas exogenous Ca²⁺ entry was crucial for ERK activation in Jurkat T cells. In both cells, membrane scrambling only occurred following Ca²⁺ entry and was not blocked by inhibiting ERK phosphorylation. Furthermore, ERK proteins are strongly phosphorylated in transformed B lymphoblastic cell lines, which do not expose PS in their resting state. Overall, the data demonstrated that ERK activation and membrane scrambling are independent mechanisms. A. Arachiche, I. Badirou: These authors contributed equally to this work. Received 18 June 2008; received after revision 24 September 2008; accepted 1 October 2008     

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.