Different Concentrations Of Mg Research Articles

Studies on TL of LiF: Mg and/or Cu Exposed to Gamma and UV Rays

The thermoluminescence (TL) of LiF doped with different concentrations of Mg and/or Cu has been investigated. The glow peaks for the samples submitted to a thermal treatment and exposed to 0.26 mC.kg-1 of gamma rays or 0.4 J.cm-2 of UV or to both consecutively are analysed. The experimental results suggest that UV radiation fills the traps directly, and that each radiation, gamma or UV, fills preferentially different depth traps. UV induced peaks appear at a lower temperature than those due to gamma rays. Samples doped only with Mg (0.1 mol%) present the highest TL sensitivity to gamma rays and a further increase of Mg concentration drastically reduces the TL sensitivity. In contrast, the sensitivity to UV light is enhanced when the concentration of Mg is increased from 0.1 to 0.4 mol%. TL sensitivity to both UV and gamma rays for samples doped only with Cu decreases with the increase of Cu concentration from 0.03 to 0.12 mol%. Higher Mg and Higher Cu concentrations, when alone, reduce the TL induced by gamma rays, but Cu co-doping of Mg doped sample seems to help improve TL sensitivity.

The pH-lowering ability ofSphagnum magellanicumBrid.

AbstractThe classic explanation of the low pH in bogs attributes this phenomenon to the H+ exchange capacity of Sphagnum. However, recent researchers have challenged this theory, arguing instead that such exchange could not account for the ions measured and that organic acids were a more likely explanation. We have attempted to determine if Sphagnum can exchange sufficient hydrogen to account for the low pH of the bog surface zone. To determine cation exchange capability of Sphagnum magellanicum in relation to the common cations of natural habitats, distilled and deionized water and different concentrations of Mg2+, Ca2+, K+, and Rudolph's Sphagnum nutrient medium were tested. In these experiments Sphagnum changes the pH of a surrounding liquid medium in the pH range of 3 to 7. The cation exchange capacity of Sphagnum magellanicum follows the series K+<Mg2+<Ca2+. Rudolph's medium consists of many compounds that resulted in much less hydrogen being released than from solutions of single compounds. Differen...

Dissociation of calcium from the phosphorylated calcium-transporting adenosine triphosphatase of sarcoplasmic reticulum: kinetic equivalence of the calcium ions bound to the phosphorylated enzyme

The internalization of 45Ca by the calcium-transporting ATPase into sarcoplasmic reticulum vesicles from rabbit muscle was measured during a single turnover of the enzyme by using a quench of 7 mM ADP and EGTA (25 degrees C, 5 mM MgCl2, 100 mM KCl, 40 mM MOPS.Tris, pH 7.0). Intact vesicles containing either 10-20 microM or 20 mM Ca2+ were preincubated with 45Ca for approximately 20 s and then mixed with 0.20-0.25 mM ATP and excess EGTA to give 70% phosphorylation of Etot with the rate constant k = 300 s-1. The two 45Ca ions bound to the phosphoenzyme (EP) become insensitive to the quench with ADP as they are internalized in a first-order reaction with a rate constant of k = approximately 30 s-1. The first and second Ca2+ ions that bind to the free enzyme were selectively labeled by mixing the enzyme and 45Ca with excess 40Ca, or by mixing the enzyme and 40Ca with 45Ca, for 50 ms prior to the addition of ATP and EGTA. The internalization of each ion into loaded or empty vesicles follows first-order kinetics with k = approximately 30 s-1; there is no indication of biphasic kinetics or an induction period for the internalization of either Ca2+ ion. The presence of 20 mM Ca2+ inside the vesicles has no effect on the kinetics or the extent of internalization of either or both of the individual ions. The Ca2+ ions bound to the phosphoenzyme are kinetically equivalent. A first-order reaction for the internalization of the individual Ca2+ ions is consistent with a rate-limiting conformational change of the phosphoenzyme with kc = 30 s-1, followed by rapid dissociation of the Ca2+ ions from separate independent binding sites on E approximately P.Ca2; lumenal calcium does not inhibit the dissociation of calcium from these sites. Alternatively, the Ca2+ ions may dissociate sequentially from E approximately P.Ca2 following a rate-limiting conformational change. However, the order of dissociation of the individual ions can not be distinguished. An ordered-sequential mechanism for dissociation requires that the ions dissociate much faster (k greater than or equal to 10(5) s-1) than the forward and reverse reactions for the conformational change (k-c = approximately 3000 s-1). Finally, the Ca2+ ions may exchange their positions rapidly on the phosphoenzyme (kmix greater than or equal to 10(5) s-1) before dissociating. A Hill slope of nH = 1.0-1.2, with K0.5 = 0.8-0.9 mM, for the inhibition of turnover by binding of Ca2+ to the low-affinity transport sites of the phosphoenzyme was obtained from rate measurements at six different concentrations of Mg2+.

Uptake of Iron by Bifidobacterium thermophilum Depends on the Metal Content of Its Growth Medium

Bifidobacterium thermophilum was grown in the trypticase-protease-yeast extract medium containing different concentrations of Mg2+, Ca2+, and Fe3+, and Fe2+ uptake was then measured in cells grown in the presence of metal ions. Cells that grew in metal-depleted media took up more iron than was the case with cells grown in metal-replete media. Such differences were not due to a necessity to transport iron against a concentration gradient, because soluble iron content was the same in cells grown in all types of media. Moreover, iron uptake could be diminished in cells grown only in the presence of increased amounts of Ca2+ or of Mg2+. Iron uptake in cells grown in metal-depleted media was dependent on iron concentration, and the uptake was virtually abolished at 0°C and after heating the cells at 65°C for 20min. A possible explanation for this behavior is that the metals suppress the expression of a metal transporter.

Effects of cations on Methanosarcina thermophila TM-1 growing on moderate concentrations of acetate: production of single cells

The effects of different concentrations of Mg2+, Ca2+, or Na+ on the morphology and growth of Methanosarcina thermophila TM-1 growing on acetate at concentrations comparable with those found in anaerobic digestors was studied. At 30 mm Mg2+ or less, M. thermophila grew as large aggregates that settled rapidly. At 100 mm Mg2+ or more, the bacteria grew as single cells or a mixture of single cells and small aggregates is suspended culture. Mg2+ was necessary for growth and could not be substituted by addition of either Ca2+ or Na+. The optimal Mg2+ concentration was 30 mm and no growth was observed at 400 mm Mg2+. Cultures could be adapted to 300 mm Mg2+ without a change in growth rate. Added Ca2+ was not required for growth and had no effect on cell morphology. Inhibition by Na+ was directly related to the Mg2+ concentration. When the Mg2+ was 0.05 mm or less, 0.35 m Na+ completely inhibited growth. However, more Na+ was required for inhibition at higher Mg2+ concentrations. The same inhibitory effect of Na+ was observed when the temperature was 52°C or 45°C. The potential for disaggregation of Methanosarcina aggregates in anaerobic digestor environments was discussed.

A structural study of phosphate‐methylated d(CpG)n and d(GpC)n DNA oligomers. Implications of phosphate shielding for the isomerisation of B‐DNA into Z‐DNA

AbstractIt is shown that the phosphate‐methylated DNA miniduplex d(CpG)2 adopts a left‐handed Z‐type structure, whereas the phosphate‐methylated miniduplex d(GpC)2 is right‐handed. Furthermore, it is shown that elongation of the systems to the tetramer level results in right‐handed duplexes with rather low stability. The phosphate‐methylated hexamer d(CpGpCpGpCpG) is present in the single‐strand form. It is suggested that these results are of interest in the understanding of the exact role of salt cations in stabilizing the Z‐DNA structure of natural duplexes d(CpG…CpG)2 in high salt solution, since the methylated phosphate groups in fact mimic the situation of complete phosphate‐charge shielding. Therefore, it is concluded that exclusive cation‐phosphate complexation in the d(CpG)2 segments stabilizes the Z structure. 31P‐NMR experiments on the natural duplex d(CpGpCpGpCpG)2 at different concentrations of Mg2+ provided independent proof for the proposed model.

Structure of helical RecA-DNA complexes: II. Local conformational changes visualized in bundles of RecA-ATPγS filaments

Complexes of RecA-DNA filaments, formed in the presence of a non-hydrolyzable ATP analog, ATPγS, aggregate together into regular bundles in the presence of Mg 2+. Electron micrographs of several different forms of RecA-double-stranded DNA bundles have been analyzed: bundles of six supercoiled filaments at two different concentrations of Mg 2+, and bundles of three supercoiled filaments at a single concentration of Mg 2+. The bundles are all characterized by a regular left-handed supercoiling of the component filaments arising from the non-integral number of RecA subunits per turn of the RecA helix in these aggregates, about 6.15 units/turn. When single-stranded DNA is used instead of double-stranded DNA, regular aggregates composed of many filaments are formed. These aggregates do not supercoil, consistent with a symmetry of the component filaments of close to 6.0 units/turn. These different structures have provided a strong confirmation of the analysis of isolated RecA filaments. Since different RecA protomers within the component filaments of these aggregates are in different environments, they have provided a direct view of different conformations that RecA subunits may adopt within the same filament as a result of non-equivalent contacts. The conformational changes we have visualized are quite large, with apparent movements of mass over distances greater than 2 nm. The RecA-mediated strand exchange reaction is a highly dynamic process, which involves both the unwinding and stretching of DNA, in addition to the physical movement of DNA strands. It is quite likely, therefore, that the different conformations of RecA subunits seen in these aggregates represent different states of RecA during its enzymatic strand exchange activity.

Matrix magnesium and the permeability of heart mitochondria to potassium ion.

Isolated beef heart mitochondria were treated with A23187 in the presence of different concentrations of Mg2+ or EDTA to establish varying levels of total mitochondrial Mg2+. The Mg2+ content was related to the rate of passive swelling of the mitochondria in potassium acetate and other potassium salts in which swelling is presumed to depend on K+ entry via an endogenous K+/H+ antiport. Swelling in these salts does not commence until Mg2+ has been depleted from an initial value of 36 nmol X mg-1 of protein to 8 nmol/mg-1, or less. Below this level, swelling increases linearly with decreasing Mg2+ to a maximum rate at 2 nmol of Mg2+ X mg-1. Rotenone-treated heart mitochondria suspended in 75 mM potassium acetate at pH 7.80 show no delta pH by 5,5-dimethyl-2,4-oxazolidinedione distribution. Distribution of methylamine also shows essentially no delta pH under these conditions when allowance is made for binding of [14C]methylamine by mitochondrial membranes under these conditions. Addition of A23187 results in a small and transient delta pH (delta pH less than 0.14, acid interior) as measured by methylamine distribution. Estimation of the maximum matrix free Mg2+ concentration from the maximum delta pH observed and the external free Mg2+ concentration at equilibrium with A23187 shows that swelling is not initiated until matrix free Mg2+ is decreased to below 150 microM. An independent estimate of free Mg2+ using a null-point procedure gives a lower, but quite similar value (50 microM) for maximum matrix free Mg2+ when swelling commences. The large depletion of total and free Mg2+ that is required to activate swelling in potassium acetate (and presumably K+/H+ antiport activity) does not appear to be compatible with previous indications that free Mg2+ acts as a "carrier brake" to regulate K+ extrusion from the mitochondrion on such an antiport (Garlid, K. D. (1980) J. Biol. Chem. 255, 11273-11279). The removal of a tightly bound component of mitochondrial Mg2+ is closely related to increased K+ permeability and increased passive swelling in potassium salts. This Mg2+ appears to play a role in the maintenance of mitochondrial membrane structure and integrity.

Human lymphocytic ecto-5'-NT: its determination and partial characterization.

The enzyme purine 5′-nucleotidase (ecto-5#x2032;-NT, EC.3.1.3.5) located on the outer membrane of cells (e.g. lymphocytes), catalyses the hydrolysis of the phosphate group from purine mononucleotides. This ecto-enzyme can serve as a marker of T- and B-cell maturation(1,2,3). So far little is known about kinetic properties of ecto-5′-NT on human lymphoid cells. Controversial results have been published about ecto-5′-NT activities on human peripheral blood lymphocytes (PBL). These may be attributed to differences in assay conditions such as choice of proper substrate, the use of different concentrations of Mg2+ the use of α, ß-methylene adenosine diphospho-nate (AOPCP) as a specific inhibitor of ecto-5′-NT activity and the concentration of this compound in the assay. In the present study we investigated kinetic properties and substrate specificity of the enzyme on intact human PBL in addition to the inhibition by AOPCP as well as the influence of Mg2+. Furthermore, we determined ecto-5′-NT activities on normal PBL and on lymphocytes from patients with immunodeficiency diseases, including a patient with purine nucleoside Phosphorylase deficiency (4). Also the amount of ecto-5′-NT enzyme protein was determined on lymphocytes of the latter patient.KeywordsPurine NucleosidePurine Nucleoside PhosphorylaseMixed Type InhibitionHuman Lymphoid CellProper SubstrateThese keywords were added by machine and not by the authors. This process is experimental and the keywords may be updated as the learning algorithm improves.

Withdrawal of magnesium enhances coronary arterial spasms produced by vasoactive agents.

1 The influence of external magnesium ions ([Mg2+]o) on the sensitivity (i.e. EC50) and contractility (maximum response) of isolated large and small coronary arteries of the dog, obtained from different regions of the myocardium, to vasoactive agents was studied. 2 Removal of [Mg2+]o from the physiological salt solution enhanced, while elevation in [Mg2+]o to 4.8 mM, lowered the contractile sensitivity to three different agents, 5-hydroxytryptamine (5-HT), angiotensin II and KCl. 3 Contractility, of both large and small coronary arteries, to 5-HT and angiotensin II was potentiated and depressed, respectively, by withdrawal and elevation of [Mg2+]o; maximum responses to KCl were not altered by 0 or 4.8 mM [Mg2+]o. 4 Cumulative concentration-contractile effect curves to CaCl2 were shifted leftward on removal of [Mg2+]o; elevation of [Mg2+]o to 4.8 mM shifted the CaCl2 concentration-effect curves to the right. Maximal contractile responses to CaCl2 were enhanced by removal of, and reduced by elevation of, [Mg2+]o. 5 The calcium channel blocking agent, verapamil (10(-6)M), inhibited completely contractile responses to KCl; contractile responses elicited by angiotensin II and 5-HT were attenuated by verapamil. 6 A variety of pharmacological antagonists (phentolamine, propranolol, methysergide, atropine, diphenhydramine), as well as use of a prostaglandin cyclo-oxygenase inhibitor, did not modify the altered contractile responses evoked by angiotensin II or KCl in different concentrations of Mg2+. 7 These results suggest: (1) [Mg2+]o may exert considerably greater influence on receptor-operated rather than membrane-potential sensitive channels involved in Ca2+ transport in coronary arterial smooth muscle; (2) Mg2+ interferes with the affinity (binding) of certain agonists (5-HT and angiotensin II) for their respective receptors in coronary vascular muscle; and (3) a functional pool of Ca2+ which is resistant to Ca2+-depletion, but accessible to activation by 5-HT and angiotensin II is present in canine coronary arterial smooth muscle.

Mitochondrial ribosome assembly in Neurospora. Structural analysis of mature and partially assembled ribosomal subunits by equilibrium centrifugation in CsCl gradients.

In Neurospora, one protein associated with the mitochondrial small ribosomal subunit (S-5, Mr 52,000) is synthesized intramitochondrially and is assumed to be encoded by mtDNA. When mitochondrial protein synthesis is inhibited, either by chloramphenicol or by mutation, cells accumulate incomplete mitochondrial small subunits (CAP-30S and INC-30S particles) that are deficient in S-5 and several other proteins. To gain additional insight into the role of S-5 in mitochondrial ribosome assembly, the structures of Neurospora mitochondrial ribosomal subunits, CAP-30S particles, and INC-30S particles were analyzed by equilibrium centrifugation in CsCl gradients containing different concentrations of Mg+2. The results show (a) that S-5 is tightly associated with small ribosomal subunits, as judged by the fact that it is among the last proteins to be dissociated in CsCl gradients as the Mg+2 concentration is decreased, and (b) that CAP-30S and INC-30S particles, which are deficient in S-5, contain at most 12 proteins that are bound as tightly as in mature small subunits. The CAP-30S particles isolated from sucrose gradients contain a number of proteins that appear to be loosely bound, as judged by dissociation of these proteins in CsCl gradients under conditions in which they remain associated with mature small subunits. The results suggest that S-5 is required for the stable binding of a subset of small subunit ribosomal proteins.

Effect of Zn and Mg on the formation of whitlockite in human subgingival calculus.

X-ray diffraction analyses were carried out from pooled samples of old subgingival calculus. Also the concentration of Ca, Mg, Zn, Sr, Pb, Fe and Cu from these samples were determined by means of atomic absorption spectrophotometry. The comparison of the samples containing almost the same Zn concentration and two different concentrations of Mg (9 mg/g and 16 mg/g) showed an increase of 2.0.10 and 220 whitlockite reflections with an increasing Mg concentration. The increase of Mg concentration shifted whitlockite reflections suggesting a contraction of a-axis. The increase of Zn concentration showed an increase of 2.0.10 and 220 reflections indicating the fitness of Zn into the lattice of whitlockite. No changes of a-axis were detectable. When comparing all diffractograms and the results obtained from chemical analyses, the presence of Zn-MG-whitlockite proved evident.

The forced magnetostriction of single crystal gadolinium

Complexes of RecA-DNA filaments, formed in the presence of a non-hydrolyzable ATP analog, ATPγS, aggregate together into regular bundles in the presence of Mg2+. Electron micrographs of several different forms of RecA-double-stranded DNA bundles have been analyzed: bundles of six supercoiled filaments at two different concentrations of Mg2+, and bundles of three supercoiled filaments at a single concentration of Mg2+. The bundles are all characterized by a regular left-handed supercoiling of the component filaments arising from the non-integral number of RecA subunits per turn of the RecA helix in these aggregates, about 6.15 units/turn. When single-stranded DNA is used instead of double-stranded DNA, regular aggregates composed of many filaments are formed. These aggregates do not supercoil, consistent with a symmetry of the component filaments of close to 6.0 units/turn. These different structures have provided a strong confirmation of the analysis of isolated RecA filaments. Since different RecA protomers within the component filaments of these aggregates are in different environments, they have provided a direct view of different conformations that RecA subunits may adopt within the same filament as a result of non-equivalent contacts. The conformational changes we have visualized are quite large, with apparent movements of mass over distances greater than 2 nm. The RecA-mediated strand exchange reaction is a highly dynamic process, which involves both the unwinding and stretching of DNA, in addition to the physical movement of DNA strands. It is quite likely, therefore, that the different conformations of RecA subunits seen in these aggregates represent different states of RecA during its enzymatic strand exchange activity.