Role Of Magnesium Ions Research Articles

Ethanol and magnesium ions inhibit [formula omitted] synaptic potentials in an interactive manner

The role of magnesium ions in the inhibitory effect of ethanol on NMDA receptor-mediated population synaptic potentials (pEPSPs) in area CA 1 of the hippocampus of the adult rat, was studied. The excitatory amino acid (non-NMDA) receptor antagonist, DNQX and the GABA A channel antagonist, picrotoxin, were used to pharmacologically isolate NMDA-mediated pEPSPs. In the presence of a physiological concentration of magnesium (1.0 mM), ethanol (25–100 mM) inhibited NMDA-mediated pEPSPs, with an apparent EC 50 of approximately 50 mM. The ability of ethanol to inhibit NMDA-mediated pEPSPs was reduced when the slices were incubated in the absence of magnesium. Concentrations of ethanol, in the range of 50–200 mM (apparent EC 50 100 mM), were required to inhibit NMDA-mediated pEPSPs, in the absence of added magnesium. Combination studies of these two antagonists indicated that the sensitivity of NMDA-mediated pEPSPs to one antagonist was not altered by the presence of the other. This finding suggests that the affinity of each antagonist binding site is not affected by the presence of the other antagonist. In the case of ethanol, its low maximum antagonist efficacy may require larger concentrations of ethanol to inhibit NMDA-mediated pEPSPs, in the absence of other non-competitive antagonists such as magnesium.

Silicon membrane interface for the direct analysis of Kathon CG in aqueous solutions and cosmetic emulsions

An easy determination of Kathon CG, an antimicrobial agent widely used in cosmetic and toiletry products, has been achieved by means of silicone membrane interfaced mass spectrometry. Low levels of the above preservative (up to p.p.b.) could be easily detected in both aqueous solutions and cosmetic emulsions. Valuable information has been obtained on the stabilization and decomposition processes to which the organic components of Kathon CG are subject. The role of magnesium ions, which are present as a stabilizing agent in Kathon CG formulation, in these processes has been investigated, leading to the identification of some degradation products.

Magnesium ion is beneficial in hypothermic crystalloid cardioplegia

The role of magnesium ion and its relation to the calcium concentration of cardioplegic solutions was reexamined in this study. Isolated rat hearts were used with an oxygenated modified Krebs-Henseleit bicarbonate buffer as perfusion medium. The hearts were arrested for 20 minutes at 37 °C or 90 minutes at 24 °C. Treatment groups received one dose of nine possible cardioplegic solutions containing magnesium (0, 1.2, or 15 mmol/L) and calcium (0.05, 1.5, or 4.5 mmol/L). Ninety-six percent of the 75 magnesium-treated hearts recovered, regardless of the calcium concentration, in contrast to a 52% recovery rate in the 69 hearts that did not receive magnesium. The addition of 15 mmol/L Mg 2+ to a cardioplegic solution containing no magnesium but 0.05 mmol/L Ca 2+ significantly increased ( p < 0.01) the percent recovery of the following parameters of cardiac function: systolic pressure, 74% to 93% (37 °C), 64% to 98% (24 °C); cardiac output, 76% to 101% (37 °C), 71% to 102% (24 °C); stroke work, 64% to 104% (37 °C), 52% to 99% (24 °C); and adenosine triphosphate level, 75% to 83% (37 °C), 58% to 90% (24 °C). There were significant reductions ( p < 0.03) in percent recovery (37 °C and 24 °C) of cardiac output, stroke work, and adenosine triphosphate level in the groups that contained 0 or 15 mmol/L Mg 2+ as the calcium concentration was increased from 0.05 to 4.5 mmol/L. Significant progressive augmentation of ventricular recovery and decreased overall mortality is produced at 37 ° and 24 °C with cardioplegia containing high levels of magnesium and low levels of calcium. These data demonstrate the importance of the Mg 2 + / Ca 2 + relation in an oxygenated crystalloid solution with a pH of 7.45, carbon dioxide tension of 40 mm Hg, and oxygen tension of 750 mm Hg containing 142 mmol/L Na +.

Reduction of Nitrostyrenes to Nitroalkanes with a NADH Grafted Model

Abstract Grafting of the 1,4-dihydronicotinamide structure on a Merrifield type resin is described. With this reagent, arylnitroethanes have been obtained by regioselective reduction of β-nitrostyrenes. The yields are good and no dimeric compounds are formed. The role of magnesium ions in these reductions is different from that observed with classical NADH models.

The roles of magnesium ions in the reaction catalysed by phosphofructokinase from Trypanosoma brucei.

The involvement of Mg2+ ions in the reaction catalysed by phosphofructokinase from Trypanosoma brucei was studied. The true substrate for the enzyme was shown to be the MgATP2-complex, and free Mg2+ ions are also required for enzyme activity. At concentrations of MgATP2- of 2.92 mM and greater, and a fructose 6-phosphate concentration of 1 mM and in the presence of EDTA as a Mg2+ buffer, the Km value for Mg2+ was determined to be 294 +/- 18 microM. Neither MgATP nor free ATP is an inhibitor of the enzyme, although apparent inhibition by the latter can be observed as a consequence of the decrease in free Mg2+ by chelation.

Magnesium deprivation inhibits the expression of differentiation-related phenotypes in human promyelocytic leukemia HL-60 cells.

The role of magnesium ions in the differentiation of human promyelocytic leukemia HL-60 cells was investigated. When HL-60 extracellular magnesium was deficient (less than 0.01 mM), the total intracellular magnesium content and [3H] leucine incorporation rates decreased to 61 and 28%, respectively, on day 3. When the cells were treated with various inducers (100 nM 1 alpha, 25 dihydroxyitamine D3 (1,25(OH)2D3), 100 nM beta-all-trans retinoic acid (RA), 20 nM 12-o-tetradecanoyl phorbol-13-acetate (TPA), 1.25% dimethylsulfoxide (DMSO) and 30 nM aclacinomycin (AcM] in magnesium-deficient medium, the expression of differentiation-related phenotypes (nitroblue tetrazolium (NBT) reducing ability, nonspecific esterase (NSE) activity and monoclonal antibody, OKM1 binding activity) was almost completely inhibited. After a 2-day treatment with 100 nM 1,25(OH)2D3 in magnesium-deficient medium, the expression of differentiation-related phenotypes was restored by further incubation in the absence of inducer in standard magnesium medium (0.4 mM). These results suggested that magnesium deprivation inhibited the expression of HL-60 differentiation-related phenotypes but not their commitment to differentiation. These phenotypes were expressed without inducer in standard magnesium medium after a 2-day simultaneous treatment with 1,25(OH)2D3 and cyclohexamide (protein synthesis inhibitor) in magnesium-deficient medium, but not after simultaneous pretreatment with 1,25(OH)2D3 and alpha-amanitin (RNA synthesis inhibitor). Thus, it was suggested that the magnesium-requiring step in HL-60 cell differentiation is in protein but not mRNA synthesis. This conclusion is supported by the findings that changes in c-myc and c-fms mRNA levels in HL-60 cells treated with 100 nM 1,25(OH)2D3 in magnesium-deficient medium and those in standard magnesium medium were the same. In addition, dibutyryl cyclic adenosine monophosphate (dbc AMP) could restore expression of differentiation-related phenotypes inhibited by magnesium deprivation but not those inhibited by cyclohexamide, even though magnesium deprivation inhibited protein synthesis as much as did cyclohexamide. This suggests that magnesium-requiring step in HL-60 cell differentiation is different from that inhibited by cyclohexamide.

Magnesium-induced mitochondrial polymorphism and changes in respiratory metabolism in the fission yeast, Schizosaccharomyces pombe

The role of magnesium ions in controlling mitochondrial structure and function in the fission yeast, Schizosaccharomyces pombe, has been studied. Results show that in control cultures of S. pombe grown in the presence of magnesium, cells follow predominantly a fermentative pathway of metabolism. The mitochondria, as visualized by electron microscopy, are large but few in number, and appear irregularly branched with indistinct cristae. On depletion of the magnesium supply, cell division ceases after about 4 hours after which there is an increase in respiration. The mitochondria increase in number and become small with well-defined cristae. On replenishment of magnesium ions mitochondria seem to fuse and there is a gradual restoration of the respiratory metabolism characteristic of control cells.

Properties of the primer-binding site and the role of magnesium ion in primer-template recognition by KB cell DNA polymerase alpha.

Properties of the primer-binding site and the role of magnesium ion in primer-template recognition by KB cell DNA polymerase alpha.

Human hypoxanthine guanine phosphoribosyltransferase. The role of magnesium ion in a phosphoribosylpyrophosphate-utilizing enzyme.

The role of Mg ions in the hypoxanthine guanine phosphoribosyltransferase-catalyzed reaction have been studied using accurate values of proton and Mg stability constants of phosphoribosylpyrophosphate (P-Rib-PP) determined from pH titration data. The results obtained favor the conclusion that the dimagnesium salt of P-Rib-PP is the true substrate of the enzyme. The other species of P-Rib-PP do not appreciably affect the initial reaction rate. The inhibition of the hypoxanthine guanine phosphoribosyltransferase-catalyzed reaction observed at high MgCl2 concentration can be attributed to a competitive inhibition of Mg2+ with respect to the dimagnesium salt of P-Rib-PP, suggesting that these ionic species bind to the same enzyme form. At a fixed [P-Rib-PPtot], the concentration of its dimagnesium complex is a sigmoidal function of MgCl2 concentration, suggesting that caution must be employed in the interpretation of sigmoidal saturation curves for P-Rib-PP-utilizing enzymes when low and not constant concentrations of the divalent cation are used.

Tyrosyl-tRNA synthetase of Escherichia coli B. Role of magnesium ions in the reaction catalyzed by the enzyme.

Using EDTA‐dialyzed tyrosyl‐tRNA synthetase and tRNA, which retain 0.8 and 0.25 atom of Mg2+ per molecule, respectively, tyrosine activation as well as tyrosyl‐tRNA formation were investigated in the absence of added magnesium ions. It is shown that the tyrosyladenylate · enzyme complex is still formed, but the rate of the reaction is reduced by a factor of 104. The rate of the ATP‐PPi exchange reaction, under these conditions, is reduced by a factor of 4 · 104. In the presence of pyrophosphate the predominant reaction is not the pyrophosphorolysis of the enzyme‐bound tyrosyladenylate but its hydrolysis.The rate of tyrosyl‐tRNA formation, starting with free ATP and tyrosine and in the presence of spermidine, was only 15 times lower than in the presence of Mg2+. Spermidine has no effect on the rate of the ATP‐PPi exchange reaction.

The role of magnesium ions in β-galactosidase-catalysed hydrolyses. Studies on charge and shape of the β-galactopyranosyl-binding site

1. beta-d-Galactopyranosyl trimethylammonium bromide is a competitive inhibitor of beta-galactosidase, K(i)=1.4+/-0.2mm at 25 degrees C. 2. Tetramethylammonium bromide is not an inhibitor (K(i)>0.2m). 3. The kinetics of deactivation of Mg(2+)-saturated, and of inhibitor-and Mg(2+)-saturated, enzyme in 10mm-EDTA are similar. 4. The apparent K(i) for the glycosylammonium salt is approx. 2.2mm in the absence of Mg(2+). 5. It is therefore concluded that Mg(2+) and the inhibitor bind independently, and that the Mg(2+) does not act as an electrophilic catalyst. 6. Complexant fluorescence measurements indicate binding of 1 Mg(2+) ion per 135000-dalton protomer. 7. This stoicheiometry is confirmed by equilibrium dialysis. 8. 1,6-Anhydrogalactopyranose is neither a substrate (k(cat.)/K(m)< 3x10(-2)m(-1).S(-1)) nor an inhibitor (K(i)>0.2m). 9. Considerations of conformations available to the cationic inhibitor and to the anhydrogalactose indicate that the substrate is bound with the pyranose ring in a conformation not greatly different from the normal chair (C1) conformation.

Role of magnesium ion on the interaction between chromomycin A 3 and deoxyribonucleic acid

Role of magnesium ion on the interaction between chromomycin A 3 and deoxyribonucleic acid

Tertiary structure and function of transfer-RNA

In analogy to the globular protein structures the predominant stabilization factor of which is surface energy a compact model with the smallest possible surface of the tertiary structure of t-RNA is suggested. The principle of folding is — according to the clover leaf model — the superposition of the three leaves. The three loops form a ring (loop-stack). The stem can be placed on this molecular body bringing the CCA end into the vicinity of the loop-stack, where the CCA end can be bound. The structures of the RNA chain are subordinated to this globular structural principle. Under the influence of the sequence the CCA end is able to undergo structural changes, thus allowing to explain the role of t-RNA in the aminoacylation process and the structural differences between t-RNA, aminoacyl-t-RNA, and peptidyl-t-RNA. Furthermore it is possible to comment on the existence of the characteristic and modified bases, the role of magnesium ions and the chemical reactions of these compounds.

The role of magnesium ion in the adenine phosphoribosyltransferase reaction.

Low concentrations of magnesium ion stimulate, and high concentrations inhibit, the adenine phosphoribosyltransferase reaction. The stability constant of the Mg–pyrophosphoryl moiety of phosphoribosylpyrophosphate was assumed to be the same as that of Mg–adenosine triphosphate; the stability constant of the Mg–phosphoryl moiety of phosphoribosylpyrophosphate was assumed to be the same as that of Mg–adenosine monophosphate, and the concentration of the monomagnesium complex of phosphoribosylpyrophosphate was calculated as a function of magnesium ion and phosphoribosylpyrophosphate concentrations. The good correspondence between these curves and those of initial velocity under the same conditions suggest that the monomagnesium complex of phosphoribosylpyrophosphate is the true substrate of this reaction.

1978. Ametryne disposal by the rat: Oliver, W. H., Born, G. S. & Ziemer, P. L. (1969). Retention, distribution, and excretion of ametryne (2-methylmercapto-4-ethylamino-6-isopropylamino- s-triazine) in the rat. J. agric. Fd Chem.17, 1207

Organophosphate pesticides (OPs) inhibit both true and pseudo-cholinesterases by reaction with the hydroxyl group of serine in their active sites. Poisoning with OPs is commonly seen in clinics. A common antidote for OP poisoning is atropine but, after ageing and OP dealkylation, even oximes could not be effective. It has been shown that oximes are not always useful in management of OP poisoning. On the other hand, magnesium has been found effective in both clinical and experimental studies. Studies to find more effective antidotes for OP poisoning are in progress. Presently, the possible role of magnesium ion in catalysis of reaction of dichlorvos (2,2-dichlorovinyl dimethyl phosphate, DDVP), a water-soluble OP, with serine is proposed. The hydroxyl group of serine could be a target to which DDVP can react. Nucleophilic attack of pralidoxime to DDVP was previously investigated. To confirm the idea, data were derived from recent and previous research on the role of magnesium in phosphoryl group transfer reactions. Possible reactions of serine and pralidoxime with DDVP in the absence and the presence of magnesium ion were separately investigated theoretically.We propose that the chemical reaction of serine with DDVP exclusively occurs in the presence of a magnesium divalent cation, whereas the reaction of pralidoxime with DDVP occurs independent of the presence of the magnesium ion. The role of the dissociation constant (pKa) of functional groups in these reactions seems important.It is suggested that application of serine in combination with the magnesium cation can become a more efficient antidote for treatment of OP poisoning.

The Role of Magnesium Ions in the Growth of Salmonella Phage Anti-R

SUMMARY: Magnesium or certain other divalent metal ions are needed for the adsorption of phage anti-R to its host, a ‘rough’ strain of Salmonella typhi. In medium containing magnesium ions the infected organisms burst after a latent period of about 20 min. at 37° but when infected organisms are diluted into medium without added divalent metal ions phage growth is considerably inhibited. A rapid increase in phage titre occurs when magnesium ions are added late, i.e. at some time after the end of the normal latent period, to dilute cultures of phage-infected organisms. During the interval between infection and this late addition of magnesium ions no appreciable numbers of infective intracellular phage were detected after ultrasonic disruption of the organisms. It is concluded that in addition to being an adsorption cofactor, magnesium functions at some late stage in phage development. Phage anti-R is probably related to ϕX 174; it consists of particles approximately 30 mμ in diameter and the intact phage reacts similarly with formaldehyde.

Role of magnesium ion in the initiation of ventricular fibrillation produced by acute coronary occlusion.

The incidence of ventricular fibrillation following acute coronary occlusion in dogs was reduced by perfusing the ischemic area of the myocardium with Locke-Ringer's solution and solutions of magnesium ion in physiological saline. In contrast, normal serum concentrations of magnesium in 5 per cent dextrose appeared to induce ventricular fibrillation in these circumstances. The results suggest that changes in the concentration of magnesium and sodium ion in extracellular fluid may initiate ventricular fibrillation in the ischemic heart.