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PubMed1997

Ferrous iron uptake by a magnesium transport system is toxic for Escherichia coli and Salmonella typhimurium.

At low magnesium concentrations, Escherichia coli and Salmonella typhimurium LT2 accumulate ferrous iron independent of the ferrous iron transport system feo. Mutant strains with mutations in the magnesium transport gene corA accumulated less ferrous iron than the parent strains. corA+ and corA strains also differed in their sensitivity to ferrous iron under oxic conditions. corA mutants were more resistant to ferrous iron than their parent corA+ strains. Part of the ferrous iron accumulated can be chased by the addition of magnesium. Much less iron was chased when ferric iron was taken up by the siderophore ferrichrome. These results may indicate that the intracellular metabolism of the iron taken up by these systems differs and that it depends on the uptake route of the iron.

Bacterial Proteins↗
PubMed1980

Substrate-specificity studies on protochlorophyllide reductase in barley (Hordeum vulgare) etioplast membranes.

1. The substrate specificity of the enzyme protochlorophyllide reductase in barley (Hordeum vulgare) etioplasts was investigated. 2. It was shown that naturally occurring esterified protochlorophyllide and chemically prepared protochlorophyllide methyl ester are not substrates for the enzyme, suggesting an important role for the C-7 carboxylic acid group in binding of the porphyrin to the enzyme. 3. Removal of magnesium from the protochlorophyllide leads to inactivity of the compound as a substrate for the enzyme. However, activity can be restored by replacing the magnesium with zinc, whereas nickel, copper or cobalt failed to restore substrate activity. 4. Binding of the second substrate, NADPH, to the enzyme probably occurs through the 2'-phosphate group in the coenzyme.

Chloroplasts↗
PubMed1994

Cercospora beticola toxins. VII. Fluorometric study of their interactions with biological membranes.

The interactions of two beticolins, Cercospora beticola toxins, and of their magnesium complexes with liposomes or plasma membrane were studied. The fluorometric pH titration curves of beticolins in liposomes and in plasma membranes reveal the presence of the dissociated form of beticolins. The concentration of the magnesium complex in these membranes increases at high pH. The partition coefficient of beticolin-1 on liposomes is 3-fold higher than that of beticolin-2 and the fluorescence of both compounds on liposomes is similar. The addition of magnesium to liposomes causes a 40-fold and 20-fold increase in the partition coefficient of beticolin-1 and -2, respectively, as a result of the interactions between membrane, magnesium and beticolins. Beticolins react to a delta pH across the liposome membrane but the formation of the magnesium complex completely abolishes this effect.

Binding Sites↗
PubMed1986

Scintigraphic assessment of neorectal motor function.

Colectomy, mucosal rectectomy, and ileal pouch-anal anastomosis have become alternatives to proctocolectomy and ileostomy for patients with ulcerative colitis or polyposis coli. The aim of this study was to develop a scintigraphic technique for assessment of the "neorectal" motor function of such patients. An artificial stool, consisting of a 7.5% dispersion of aluminum magnesium silicate in water, was labeled with 1 mCi [99mTc]sulfur colloid and instilled into the neorectum. Static pre- and postevacuation scans and dynamic acquisition scans during evacuation were taken with the patient seated on a commode. The imaging provided good anatomic definition of the pouch and quantitated the usual rate and percentage of neorectal evacuation at about 10 ml stool/sec and 60% of instilled stool, respectively. This technique appeared to be a safe, simple, useful tool for assessing the neorectal motor function of patients with ileal pouch-anal anastomosis.

Adult↗
PubMed2001

Differential biosynthesis of polysialic or disialic acid Structure by ST8Sia II and ST8Sia IV.

ST8Sia II (STX) and ST8Sia IV (PST) are polysialic acid (polySia) synthases that catalyze polySia formation of neural cell adhesion molecule (NCAM) in vivo and in vitro. It still remains unclear how these structurally similar enzymes act differently in vivo. In the present study, we performed the enzymatic characterization of ST8Sia II and IV; both ST8Sia II and IV have pH optima of 5.8-6.1 and have no requirement of metal ions. Because the pH dependence of ST8Sia II and IV enzyme activities and the pK profile of His residues are similar, we hypothesized that a histidine residue would be involved in their catalytic activity. There is a conserved His residue (cf. His(348) in ST8Sia II and His(331) in ST8Sia IV, respectively) within the sialyl motif VS in all sialyltransferase genes cloned to date. Mutant ST8Sia II and IV enzymes in which this His residue was changed to Lys showed no detectable enzyme activity, even though they were folded correctly and could bind to CDP-hexanolamine, suggesting the importance of the His residue for their catalytic activity. Next, the degrees of polymerization of polySia in NCAM catalyzed by ST8Sia II and IV were compared. ST8Sia IV catalyzed larger polySia formation of NCAM than ST8Sia II. We also analyzed the (auto)polysialylated enzymes themselves. Interestingly, when ST8Sia II or IV itself was sialylated under conditions for polysialylation, the disialylated compound was the major product, even though polysialylated compounds were also observed. These results suggested that both ST8Sia II and IV catalyze polySia synthesis toward preferred acceptor substrates such as NCAM, whereas they mainly catalyze disialylation, similarly to ST8Sia III, toward unfavorable substrates such as enzyme themselves.

Amino Acid Sequence↗
PubMedDate not supplied

[The effect of ionic strength on reversible inhibition of catalytic activity of acetylcholinesterase by thione phosphonates].

The effect of ionic strength was used to analyze the mechanism of reversible acetylcholinesterase inhibition by three alkoxymethylthionphosphonates. The most considerable realization of the hydrophobic interaction with the surroundings of the enzyme esteratic site was marked for n-butyl derivative (compound I). The replacement of piperidine by morpholine (compound II) resulted in a decrease of the anticholinesterase activity by an order due to enhancement of the inhibitor hydrophilicity. An increase of MgCl2 concentration promotes an enhancement of the uncompetitive component contribution for compound III contrast to compound II. Hydrophobicity of the phosphoryl part of the compound I molecule is balanced under hydrophobic interaction of the heterocyclic "cationic head" with the enzyme anionic site. The break of this equilibrium intensifies the allosteric regulation, on the one hand, and lowers the inhibitor efficiency, on the other hand.

Acetylcholinesterase↗
PubMed1994

Interactions of plant acetohydroxy acid isomeroreductase with reaction intermediate analogues: correlation of the slow, competitive, inhibition kinetics of enzyme activity and herbicidal effects.

N-Hydroxy-N-isopropyloxamate (IpOHA) is known to inhibit extremely tightly (Ki of 22 pM) the bacterial acetohydroxy acid isomeroreductase (EC 1.1.1.86) [Aulabaugh and Schloss (1990) Biochemistry 29, 2824-2830], the second enzyme of the branched-chain-amino-acid-biosynthetic pathway. Yet, although the same pathway exists in plant cells, this compound presents only very poor herbicidal action. Towards the goal of gaining a better understanding of this behaviour, we have studied the mechanism of interaction of this compound with a highly purified acetohydroxy acid isomeroreductase of plant origin, i.e. the spinach (Spinacia oleracea) chloroplast enzyme. IpOHA behaved as a nearly irreversible inhibitor of the enzyme. Encounter complex formation was very slow (association rate constant 1.9 x 10(3) M-1.s-1) and involved a single bimolecular step. Since inhibition was competitive with respect to acetohydroxy acid substrates, the time needed to achieve substantial (90%) inhibition in vitro of enzyme activity in the simultaneous presence of substrates and inhibitors was extremely long (for example of the order of hours at 1 microM IpOHA and 100 microM acetohydroxy acid substrates). Thus, under in vivo conditions, binding of the inhibitor may be so slow that it may delay considerably the time required for inhibition of the target enzyme. Simialr kinetic behaviour was observed with another reaction intermediate analogue described by Schulz, Spönemann, Köcher and Wengenmayer [(1988) FEBS Lett. 238, 375-378], 2-dimethyl-phosphinoyl-2-hydroxyacetic acid (Hoe 704), which displays a higher herbicide activity than IpOHA. The herbicidal potency of these two compounds appeared to be correlated with their rates of association with the plant acetohydroxy acid isomeroreductase, since the bimolecular rate constant for Hoe 704 (2.2 x 10(4) M-1.s-1) was higher than that for IpOHA.

Alcohol Oxidoreductases↗
PubMed2004

Preliminary results on the immobilisation of radionuclides from waters with specific adsorbers based on phosphate salts.

The present paper is focused on the ability of aluminium phosphate (ALPC), magnesium ammonium phosphate (MGPC), magnesium hydrogen phosphate (MGHPC), and calcium hydrogenphosphate (CAHPC), adsorbed onto charcoal, to immobilise actinides by adsorption from natural waters. The objective of this process is to evaluate the environmental pollution due to the actinides. Europium, thorium, protactinium, neptunyl, and uranyl ions were chosen to simulate actinides in the +3, +4, +5 and +6 oxidation state. The adsorbers were tested using natural waters samples. The adsorption trends and capacities were analysed. ALPC and MGPC exhibited a similar behaviour and adsorbed demonstrating that the +5, +4 and +3 actinide ions can be easily immobilised from natural waters and may be successfully used at pH 7-8. MGHPC may be used at a higher pH, whereas CAHPC is effective in the whole pH range. In all cases, thorium, protactinium and europium were strongly

Actinoid Series Elements↗
PubMed2006

Bias-assisted in vitro calcification of calcium disilicide growth layers on spark-processed silicon.

A dry-etch spark ablation method was used to produce calcium disilicide (CaSi2/Si) layers on silicon (Si) surfaces for the electrochemical growth of apatitic phosphates (calcium phosphate, CaP). CaSi2/Si composite electrodes readily calcify in vitro under the application of a small electric potential, and with proper treatment, the electrodeposition of CaP is localized to the sparked areas. In addition to increasing the local concentration of calcium, interfacial layers of CaSi2 on Si exhibit exceptional site selectivity towards CaP formation under bias due to the difference in conductivity between Si and CaSi2. The proposed mechanism for bias-assisted biomineralization of CaSi2/Si layers on spark-processed Si accounts for the physicochemical properties of deposited CaP films. This work also describes routes to surface modification of calcified composite electrodes with medicinally relevant compounds such as alendronate and norfloxacin. To assess the suitability of this material as a drug-delivery platform, release of the latter compound was also monitored as a function of time.

Anti-Infective Agents↗
PubMed1992

Crystal chemistry of Mg2P2O7.nH2O, n = 0, 2 and 6: magnesium-oxygen coordination and pyrophosphate ligation and conformation.

The crystal structure of the hexahydrate has been determined and is compared with the known structures of the dihydrate and two forms of the anhydrous compound. Comparisons among the structures provide some insight as to the structural role of Mg2+ as a cofactor in the ATP-ADP hydrolysis reactions of bioenergetics. Crystal data for dimagnesium pyrophosphate hexahydrate: Mg2P2O7.6H2O, M(r) = 330.66, monoclinic, P2(1)/n, a = 7.189 (2), b = 18.309 (8), c = 7.665 (5) A, beta = 92.360 (14) degrees, V = 1008.1 A3, Z = 4, Dx = 2.18 mg mm-3, F(000) = 680, mu = 0.609 mm-1 for lambda(Mo K alpha) = 0.7107 A. R(magnitude of F) = 0.047 for 937 data.

Adenosine Triphosphate↗
PubMed1995

Magnesium sulfate in exacerbations of chronic obstructive pulmonary disease.

BACKGROUND: Acute exacerbations of chronic obstructive pulmonary disease are commonly seen and difficult to treat. We sought to determine the bronchodilator efficacy of magnesium sulfate in this situation, as this compound is helpful in acute asthma. METHODS: Subjects who came to either of two Veterans Affairs emergency departments were randomized in a double-blind fashion to receive either 1.2 g of magnesium sulfate or placebo over 20 minutes after they first received albuterol, 2.5 mg by nebulization. Peak expiratory flow, dyspnea scores, arterial hemoglobin oxygen saturation by pulse oximetry, maximal inspiratory and expiratory pressures, and vital signs were monitored for 45 minutes after the start of magnesium sulfate or placebo treatment. RESULTS: Seventy-two individuals were studied. The peak expiratory flow increased 16.6% +/- 27.7% (mean +/- SD) in both groups after the initial albuterol treatment, from 121.2 +/- 55.7 L/min to 136.9 +/- 63.9 L/min. The peak expiratory flow increased from 136.7 +/- 69.7 L/min at the start of the infusion to 162.3 +/- 76.6 L/min at 30 minutes and 161.3 +/- 78.7 L/min at 45 minutes with magnesium sulfate treatment. The peak expiratory flow was 137.0 +/- 58.6 L/min on initiation of the intravenous infusion, 143.0 +/- 72.7 L/min at 30 minutes, and 143.3 +/- 70.5 L/min at 45 minutes in the placebo group. The difference in peak expiratory flow from initiation of the infusion to 30 and 45 minutes later (calculated as means of the 30- and 45-minute values) was significantly different for the two groups (25.1 +/- 35.7 L/min vs 7.4 +/- 33.3 L/min; P = 0.3); the difference was also significant when expressed as percentage increase (22.4% +/- 28.5% vs 6.1% +/- 24.4%; P = .01). There was a statistically nonsignificantly trend toward a reduced need for hospitalization in the magnesium sulfate group as compared with the placebo group (28.1% vs 41.9%; P = .25). There were no significant changes in the other parameters with either treatment. CONCLUSION: Magnesium sulfate, 1.2 g over 20 minutes after beta-agonist administration, is safe and modestly efficacious in the treatment of acute exacerbations of chronic obstructive pulmonary disease, and its bronchodilator effect is greater than that of a beta-agonist given alone and lasts beyond the period of magnesium sulfate administration.

Aged↗
PubMed1997

ATP/ADP antiporter- and aspartate/glutamate antiporter-mediated fatty acid-induced uncoupling of liver mitochondria in incubation media differing in ion composition.

Substitution of potassium cloride for sucrose in the incubation medium of liver mitochondria or addition of magnesium cloride to the sucrose medium produces a small (if any) effect on the palmitate-induced uncoupling and its sensitivity to carboxyatractylate and aspartate, but it exerts a pronounced increase in the recoupling effect of glutamate on this uncoupling. 20-40 microM cetyltrimethyl ammonium bromide increases the recoupling effect of glutamate and aspartate but decreases that of carboxyatractylate. The data are in line with suggestion that both ATP/ADP antiporter and aspartate/glutamate antiporters are involved in the fatty acid-induced uncoupling.

Amino Acid Transport Systems, Acidic↗
PubMed1975

Investigation of some materials as dry binders for direct compression in tablet manufacture. Part 5: Effects of lubricants and flow conditions.

The effect of talc, magnesium stearate, stearic acid, and Acrawax C, which are commonly used as lubricants, on the dry-binding efficiency of tragacanth, polyethylene glycol 4000, polyvinylpyrrolidone, and mannitol were investigated. The effect of Aerosil which is sometimes utilized as a flow conditioner for directly compressible powder blends was also studied. The type and concentration of lubricant or flow conditioner appeared to influence the binding efficiency of the binders investigated to various degrees. The results showed that the bonding characteristics of all the binders tested except mannitol were reduced by the addition of the lubricants and the flow conditioner.

Chemistry, Pharmaceutical↗
PubMed2006

Quality and stability analysis for the rainfall water and surface runoff water in southeast region of Beijing Municipality.

In this study, water sampling was carried out extensively through collection of natural rainfall and municipal surface runoff water samples in the southeast region of Beijing Municipality during the period of June 2002 to July 2004. Chemical tests and measurements of collected water samples were conducted in the laboratory in order to evaluate rainwater quality and to analyze chemical stability of rainwater. The test results show that the collected rainfall water and surface runoff water were soft water and belonged to bicarbonate-calcium Type-I water category. The results also show that their pH levels were closely related to the strength of alkaline constituents in the rainwater. Water quality analysis indicated that the rainwater collected from the study region had been contaminated to a certain degree by nitrogen and organic compounds from intensive human activities. Water stability analysis focuses mainly on the potential of precipitation-dissolution of carbonate calcium (CaCO3). The results show that only the rainwater samples collected from traffic roads were oversaturated with respect to CaCO3 and had a tendency to precipitate, while other rainwater samples were unsaturated with respect to CaCO3 and had the potential to keep dissolving CaCO3 into rainwater. The results obtained in this study may help to develop better rainwater utilization strategies for alleviating the growing water shortage pressure faced by the City of Beijing.

Calcium↗