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PubMed2003

Kinetic characterization of Na,K-ATPase from rabbit outer renal medulla: properties of the (alpha beta)(2) dimer.

We describe and compare the main kinetic characteristics of the (alpha beta)(2) form of rabbit kidney Na,K-ATPase. The dependence of ATPase activity on ATP concentration revealed high (K(0.5)=4 microM) and low (K(0.5)=1.4 mM) affinity sites for ATP, exhibiting negative cooperativity and a specific activity of approximately 700 U/mg. For p-nitrophenylphosphate (PNPP) as substrate, a single saturation curve was found, with a smaller apparent affinity of the enzyme for this substrate (K(0.5)=0.5 mM) and a lower hydrolysis rate (V(M)=42 U/mg). Stimulation of ATPase activity by K(+) (K(0.5)=0.63 mM), Na(+) (K(0.5)=11 mM) and Mg(2+) (K(0.5)=0.60 mM) all showed V(M)'s of approximately 600 U/mg and negative cooperativity. K(+) (K(0.5)=0.69 mM) and Mg(2+) (K(0.5)=0.57 mM) also stimulated PNPPase activity of the (alpha beta)(2) form. Ouabain (K(0.5)=0.01 microM and K(0.5)=0.1 mM) and orthovanadate (K(0.5)=0.06 microM) completely inhibited the ATPase activity of the (alpha beta)(2) form. The kinetic characteristics obtained constitute reference values for diprotomeric (alpha beta)(2)-units of Na,K-ATPase, thus contributing to a better understanding of the biochemical mechanisms of the enzyme.

Adenosine Triphosphate↗
PubMed1997

Magnesium inhibits nickel-induced genotoxicity and formation of reactive oxygen.

Nickel compounds are recognized to cause nasal and lung cancers. Magnesium is an effective protector against nickel-induced carcinogenesis in vivo, although its mechanisms of protection remain elusive. The effects of magnesium carbonate on the cytotoxicity and genotoxicity induced by nickel subsulfide were examined with respect to the inhibition of cell proliferation, micronuclei formation, DNA-protein cross-link formation, and intranuclear nickel concentration. The generation of reactive oxygen by nickel chloride was also analyzed by observing 8-hydroxy-deoxyguanosine formation from deoxyguanosine in the presence and absence of magnesium chloride. The suppression of up to 64% of the proliferation of BALB/3T3 fibroblasts by nickel subsulfide (1 microgram/ml) was reversed by magnesium. The nickel compound increased not only the number of micronuclei but also the amount of DNA-protein cross-links examined with CHO and BALB/3T3 cells, respectively. These genotoxic effects of nickel were again lessened by magnesium carbonate. In addition, the cellular accumulation of nickel increased 80-fold with nickel subsulfide treatment and decreased with magnesium carbonate treatment. Nickel also enhanced 8-hydroxy-deoxyguanosine formation in the presence of H2O2 and ascorbic acid, where magnesium played another suppressive role. In fact, inhibition by magnesium was still observed even in the absence of nickel treatment. These results suggest that the protective role of magnesium in nickel-induced cytotoxicity and genotoxicity can be attributed to its ability to reduce either the intracellular nickel concentration or reactive oxygen formation.

Animals↗
PubMed2001

Refixation of phosphates released during bio-P sludge handling as struvite or aluminium phosphate.

Phosphate release and phosphate fixation during sludge treatment of waste activated sludge was investigated with a pilot plant for enhanced biological phosphorus removal, complemented by laboratory investigations of sludge samples from different large enhanced biological phosphorus removal plants. The major part of the eliminated phosphorus in the pilot plant was due to the storage of polyphosphate in the waste activated sludge and was accompanied by an uptake of magnesium and potassium. Stabilising waste activated sludge from the enhanced biological phosphorus removal pilot plant results in a hydrolysis of polyphosphate. As a result of polyphosphate hydrolysis in stabilising systems, phosphate, magnesium and potassium are released, but only potassium remains in solution whereas magnesium and a part of the released phosphate was precipitated as struvite. Another large fraction of the released phosphate was fixed by participation of aluminium.

Aluminum Compounds↗
PubMed1995

Suppression of bitterness by sodium: variation among bitter taste stimuli.

Taste interactions between salts (NaCl, LiCl, KCl, L-arginine:L-aspartic acid, Na-acetate and Na-gluconate) and bitter-tasting compounds (urea, quinine HCl, magnesium sulphate, KCl, amiloride HCl and caffeine) were investigated. In each study binary combinations of three or four concentrations of one bitter compound with four concentrations (0, 0.1, 0.3 and 0.5 M) of one salt were rated for bitterness and saltiness using the method of magnitude estimation. In most cases, perceived bitterness was suppressed by salts, although the degree of suppression varied. In general, bitterness suppression was not accompanied by an equivalent reciprocal suppression of saltiness. Only MgSO4 and amiloride had suppressing effects on the saltiness of NaCl at the intermediate concentrations and no bitter compound affected the saltiness at the high concentrations of NaCl. Since salt suppressed the bitterness of urea effectively, a detailed analysis of suppression of the bitterness of urea by different salts was conducted. Those studies indicated that the key component in this effect was the sodium or lithium ion for two reasons: first, all three sodium salts and the lithium salt had a suppressive effect on bitterness, whereas KCl did not; secondly, the effect of a salt on suppression of the bitterness of urea was independent of its perceived saltiness; that is, NaCl, Na-acetate (which is perceived as less salty than NaCl), and Na-gluconate (which is perceived as less salty than Na-acetate) reduced bitterness comparably. These results suggest that there is a major peripheral component to the suppression of the bitterness of urea, and perhaps other bitter tasting compounds, by sodium.

Adult↗
PubMed2005

Kinetic properties of DM-nitrophen binding to calcium and magnesium.

Caged-Ca(2+) compounds such as nitrophenyl-EGTA (NP-EGTA) and DM-nitrophen (DMn) are extremely useful in biological research, but their use in live cells is hampered by cytoplasmic [Mg(2+)]. We determined the properties of Ca(2+) release from NP-EGTA and DMn by using Oregon green BAPTA-5N to measure changes in [Ca(2+)] after ultraviolet flash photolysis in vitro, with or without Mg(2+) present. A large fraction (65%) of NP-EGTA, which has a negligible Mg(2+) affinity, uncages with a time constant of 10.3 ms, resulting in relatively slow increases in [Ca(2+)]. Uncaging of DMn is considerably faster, but DMn has a significant affinity for Mg(2+) to complicate the uncaging process. With experimentally determined values for the Ca(2+) and Mg(2+) binding/unbinding rates of DMn and NP-EGTA, we built a mathematical model to assess the utility of NP-EGTA and DMn in rapid Ca(2+)-uncaging experiments in the presence of Mg(2+). We discuss the advantages and disadvantages of using each compound under different conditions. To determine the kinetics of Ca(2+) binding to biologically relevant Ca(2+) buffers, such as Ca(2+)-binding proteins, the use of DMn is preferable even in the presence of Mg(2+).

Acetates↗
PubMed1992

[The toxicokinetics of low-solubility substances (exemplified by 2 boron compounds)].

Multichamber toxicokinetic model studies of the resorption, distribution and excretion properties of poorly soluble substances in subchronic action of suspensions administered intragastrically can be the first step in prognosing the toxicokinetic properties of the inhaled aerosols of the substances mostly discharged from the respiratory into the gastrointestinal tract (GIT). The generally accepted quantitative characteristics of the particles' deposition and translocation into GIT can provide a further application of the model for a mathematical description of a prolonged inhalational exposure to some substances. This technique was tested with the boron compounds characterized by low solubility and revealed a good correlation between the prognosed and actual deposits of the substance in the organ and excretions. At the same time, detected were some qualitative and quantitative differences in the boron toxicokinetics influenced by magnesium deboride and hexaborate, which were explained by differences in their solubility.

Air Pollutants, Occupational↗
PubMed1998

Modulation by magnesium of N-methyl-D-aspartate receptors in developing human brain.

AIM: To investigate age related alterations in glutamate N-methyl-D-aspartate (NMDA) receptor binding produced by the modulatory compounds glutamate, glycine, and magnesium (Mg2+) sulphate. METHODS: The effects produced by glutamate plus glycine, and Mg2+ on the binding of [3H]MK-801, a ligand for the N-methyl-D-aspartate ion channel phencyclidine site, were measured in membrane preparations made from prefrontal cortex from human neonate (n = 5), infant (n = 6), and adult (n = 6) necropsy brains. RESULTS: Neonatal brains had the least [3H]MK-801 binding, suggesting either a low density of NMDA receptors or a more restricted access of [3H]MK-801 to cation channel sites. Infant brains had the most [3H]MK-801 binding which was stimulated to a greater extent by L-glutamate (100 microM) and glycine (10 microM) than in neonatal and adult brains. MG2+ invariably inhibited [3H]MK-801 binding. However, the Mg2+ IC50 value was higher in neonatal brain (3.6 mM) than infant (1.4 mM) and adult (0.87 mM) brains. CONCLUSION: Infant brain may have excess NMDA receptors which are hyper responsive to glutamate and glycine. The lower potency of Mg2+ to inhibit [3H]MK-801 binding in neonatal cortex may be because newborn babies have NMDA receptors without the normal complement of Mg2+ sites. The findings suggest that therapeutic NMDA receptor block in neonates requires higher concentrations of magnesium sulphate in brain tissue.

Adult↗
PubMed2006

Sodium, ammonium, calcium, and magnesium forms of zeolite Y for the adsorption of glucose and fructose from aqueous solutions.

The kinetics of adsorption by sodium, ammonium, calcium and magnesium forms of zeolite Y from aqueous solutions containing 25% w/v of either one or an equimolar mixture of glucose (G) and fructose (F) have been studied batch-wise at 50 degrees C. The adsorption of aqueous pure G was fast, while that of aqueous pure F depended on the cationic form, approaching that of G on the Mg-Y, and slowing down in the sequence of Mg2+ > NH4+ > Ca2+ > Na+ of the cations. The adsorption behavior from solutions containing both G and F indicated significant hindering effects of F on G on Na-Y. Na-Y and Mg-Y did not exhibit rate-based selectivity, while Ca-Y an NH4-Y adsorbed G faster than F. Addition of CaCl2 to the mixture of Ca-Y and aqueous solution of G and F improved the separation, by hindering the adsorption of F. Addition of NH4Cl to the mixture of the sugar solution and NH4-Y, on the other hand, had a negative effect on the separation. NH4-Y was found to be desorbing about 30% of the adsorbed sugars and this value was found to be around 50% for Ca-Y. Re-adsorption experiments resulted in similar or somewhat higher percentages of amounts adsorbed compared to adsorption on fresh samples. Both NH4-Y and Ca-Y were found to be re-adsorbing around 50% of the sugars they adsorbed on fresh samples.

Adsorption↗
PubMed2005

Sequential polymer dosing for effective dewatering of ATAD sludges.

Dewatering problems associated with the sludge from autothermal thermophilic aerobic digestion (ATAD) of sludge, result in large chemical conditioning costs for effective dewatering. A variety of chemical conditioners were used to improve dewatering, but none of them were able to dewater the sludge as desired at acceptable conditioning doses. It was found that during the digestion process, chemical precipitation of divalent cations occurred. Some of the ATAD sludge colloids were found to have a positive zeta potential and these were thought to be the precipitated divalent cations. Sequential polymer dosing using either iron or cationic polymer, followed by anionic polymer, was found to improve dewatering. The use of anionic polymer is essential and allows the use of smaller amounts of iron or cationic polymer for effective dewatering. The use of the less expensive anionic polymer along with cationic polymers has the potential to make the use of the ATAD process more economical.

Alum Compounds↗
PubMed1986

Metal-ion assisted detergent action on bacterial growth: detergent specificity and mechanism of inhibition.

Detergents in general inhibit bacterial growth. The anionic detergent, sodium lauryl sulphate (NaLS), seems to have a more specific inhibitory effect on growth of the Gram-positive Bacillus subtilis than on growth of the Gram-negative Escherichia coli. The specificity of anionic detergent towards B. subtilis has been traced to the difference in the nature of the cell wall. The inhibitory action of the detergent is markedly increased by the presence of metal ions like Cd++ or Mg++, due probably to the increase in the micellar phase, facilitating the solubilisation of bacterial species in the inner core of micelles. While metal ions like Cu++ do not influence the activity of NaLS, Na+, Ca++ or Mn++ ions seem to act against the detergent action on bacterial growth, probably by altering the structure of micelles.

Bacillus subtilis↗
PubMed2007

The Mg-oppenauer oxidation as a mild method for the synthesis of aryl and metallocenyl ketones.

Magnesium alkoxides undergo a hydride-transfer oxidation with benzaldehyde as the oxidant. This magnesium variant of the Oppenauer oxidation was used for the synthesis of polyfunctional biaryl ketones. LiCl was found to promote this reaction by enhancing the solubility of magnesium alkoxides. This mild oxidation method was especially useful for preparing ketones bearing a metallocenyl unit as well as various new ferrocenyl ketones and tricarbonylchromium complexes. This last class of ketones was reduced with the CBS catalyst (CBS=Corey-Bakshi-Shibata, diphenyl oxazaborolidine) to chiral benzhydrol complexes with high enantioselectivity enabling an asymmetric synthesis of electron-rich or -poor benzhydryl alcohols (up to 94 % ee).

Alcohols↗