PubMed Health⌕ Search

SEARCH · PubMed Health

Results for “Magnesium Compounds”

Explore indexed PubMed citations for clinical trials, systematic reviews and public health research. Read source abstracts and follow each citation to its original PubMed record.

Quote a phrase for an exact phrase match. Source license links do not imply unrestricted reuse.

At least 1,333 records · Page 74Linked to original sources
PubMed1977

ATPase and phosphatase activities from human red cell membranes. III. Stimulation of K+-activated phosphatase by phospholipase C.

Treatment of red cell membranes with pure phospholipase C inactivates (Na+ + K+)-ATPase activity and Na+-dependent phosphorylation but increases K+-dependent phosphatase activity. When phospholipase A2 replaces phospholipase C, all activities are lost. Activation of K+-dependent phosphatase by treatment with phospholipase C is caused by an increase in the maximum rate of hydrolysis of p-nitrophenylphosphate and in the maximum activating effect of K+, the apparent affinities for substrate and cofactors being little affected. After phospholipase C treatment K+-dependent phosphatase is no longer sensitive to ouabain but becomes more sensitive to N-ethylmaleimide. In treated membranes Na+ partially replaces K+ as an activator of the phosphatase. Although ATP still inhibits phosphatase activity, neither ATP, nor ATP+Na+ are able to modify the apparent affinity for K+ of K+-dependent phosphatase in these membranes.

Adenosine Triphosphatases↗
PubMed1998

Interaction of Mg2+ with the allosteric site of muscarinic M2 receptors.

Mg2+-ions have been suspected to attenuate the inhibitory effect of allosteric modulators on the dissociation of orthosteric ligands from muscarinic M2 receptors. It was aimed to gain more insight into the molecular events underlying the effect of Mg2+. The interaction of Mg2+ with the allosteric model compounds W84 (hexane-1,6-bis [dimethyl-3'-phthalimidopropylammonium bromide]) and Chin3/6 (hexane-1 ,6-bis[dimethyl-3'-¿4-oxo-2-phenyl-3,4-dihydro-2H-quinazolin-1-yl propylammonium bromide]) was studied in porcine heart muscarinic receptors, the primary binding site of which was occupied by the ligand [3H]N-methylscopolamine ([3H]NMS). The incubation buffer was composed of 4 mM Na2HPO4 and 1 mM KH2PO4 (pH 7.4, 23 degrees C). The retardation of [3H]NMS dissociation (control t1/2=5.6 min) induced by the allosteric test compounds was diminished by 3 mM Mg2+ to a greater extent than to be expected with regard to its contribution to the ionic strength of the buffer solution. Concentration-effect curves for the allosteric retardation of [3H]NMS dissociation by W84 (half maximal effective concentration EC0.5=24 nM in the absence of Mg2+) and by Chin3/6 (EC0.5=28 nM) were shifted by Mg2+ to the right in a parallel fashion. The curve-shift was compatible with a competitive interplay between Mg2+ and the modulators. The pKb-values as a measure of the antagonistic potency of Mg2+, however, differed depending on the modulator, i.e. pKb=3.4 with W84 and pKb=2.8 with Chin3/6. Mg2+ itself was capable of slowing the dissociation of [3H]NMS; the maximal retardation of [3H]NMS dissociation was about 3 fold, the concentration-effect relationship was compatible with a two-site model using the above-mentioned pKb-values as affinity constants. Since the equilibrium-binding of [3H]NMS remained unchanged up to a Mg2+-concentration of 3 mM, the cation appears to inhibit the association and dissociation of [3H]NMS to the same extent in this concentration range. Taken together, the findings indicate that Mg2+ may bind to the allosteric region of muscarinic M2 receptors and that more than one site is involved in this interaction. The sites of action may represent divalent cation binding sites.

Allosteric Site↗
PubMed2004

Unraveling the mechanism of the farnesyltransferase enzyme.

Farnesyltransferase enzyme (FTase) is currently one of the most fascinating targets in cancer research. Studies in other areas, namely in the fight against parasites and viruses, have also led to very promising results. However, in spite of the thrilling achievements in the development of farnesyltransferase inhibitors (FTIs) over the past few years, the farnesylation mechanism remains, to some degree, a mystery. This review tries to shed some light on this puzzling enzyme by analyzing seven key mechanistic dilemmas, based on recent studies that have dramatically changed the way this enzyme is currently perceived.

Animals↗
PubMed2005

Effect of transketolase substrates on holoenzyme reconstitution and stability.

The influence of transketolase substrates on the interaction of apotransketolase with its coenzyme thiamine diphosphate (TDP) and on the stability of the reconstituted holoenzyme was studied. Donor substrates increased the affinity of the coenzyme for transketolase, whereas acceptor substrate did not. In the presence of magnesium ions, the active centers of transketolase initially identical in TDP binding lose their equivalence in the presence of donor substrates. The stability of transketolase depended on the cation type used during its reconstitution--the holoenzyme reconstituted in the presence of calcium ions was more stable than the holoenzyme produced in the presence of magnesium ions. In the presence of donor substrate, the holoenzyme stability increased without depending on the cation used during the reconstitution. Donor substrate did not influence the interaction of apotransketolase with the inactive analog of the coenzyme N3'-pyridyl thiamine diphosphate and did not stabilize the transketolase complex with this analog. The findings suggest that the effect of the substrate on the interaction of the coenzyme with apotransketolase and on stability of the reconstituted holoenzyme is caused by generation of 2-(alpha,beta-dihydroxyethyl)thiamine diphosphate (an intermediate product of the transketolase reaction), which has higher affinity for apotransketolase than TDP.

Calcium↗
PubMed1988

Proton pump-linked Mg2+-ATPase activity in isolated rat liver lysosomes.

ATPase activity in highly purified rat liver lysosome preparations was evaluated in the presence of other membrane cellular ATPase inhibitors, and compared with lysosome ATP-driven proton translocating activity. Replacement of 5 mM Mg2+ with equimolar Ca2+ brought about a 50% inhibition in divalent cation-dependent ATPase activity, and an 80% inactivation of ATP-linked lysosomal H+ pump activity. In the presence of optimal concentrations of Ca2+ and Mg2+, ATPase activity was similar to that seen in an Mg2+ medium. Mg2+-dependent ATPase activity was greatly inhibited (from 70 to 80%) by the platinum complexes; cis-didimethylsulfoxide dichloroplatinum(II) (CDDP) at approximately 90 microM and cis-diaminedichloroplatinum(II) at twofold higher concentrations. Less inhibition, about 30 and 45%, was obtained with N,N'-dicyclohexylcarbodiimide and N-ethylmaleimide, and the maximal effect occurred in the 50-100 microM and 0.1-1.5 mM ranges, respectively. The concentration dependence of inhibition by the above drugs was determined for both proton pumping and ATPase activities, and half-maximal inhibition concentration of each activity was found at nearly similar values. A micromolar concentration of carbonylcyanide p-trifluoromethoxyphenylhydrazone (FCCP) prevented ATP from setting up a pH gradient across the lysosomal membranes, but stimulated Mg2+-ATPase activity significantly. ATPase activity in Ca2+ medium was also inhibited by CDDP and stimulated by FCCP, but both effects were two- to threefold less than those observed in Mg2+ medium. FCCP failed to stimulate ATPase activity in a CDDP-supplemented medium, thus suggesting that the same ATPase activity fraction was sensitive to both CDDP and FCCP. Mg2+-ATPase activity, like the proton pump, was anion dependent. The lowest activity was recorded in a F-medium, and increased in the order of F- less than SO2-4 less than Cl- approximately equal to Br-. The CDDP-sensitive ATPase activity observed, supported by Mg2+ and less so by Ca2+, may be related to lysosome proton pump activity.

Adenosine Triphosphate↗
PubMed1988

Oxidation induced by phthalocyanine dyes causes rapid calcium release from sarcoplasmic reticulum vesicles.

The copper containing phthalocyanine dyes, alcian blue, copper phthalocyanine tetrasulfonic acid, and Luxol fast blue MBSN are found to induce rapid calcium efflux from actively loaded sarcoplasmic reticulum (SR) vesicles. Alcian blue (5 microM), with 1 mM free Mg2+ triggered Ca2+ efflux at rates greater than 20 nmol/mg of SR/s. As in the case of Ca2+ efflux induced by calcium, heavy metals, or SH oxidation with Cu2+/cysteine, efflux induced by phthalocyanines is also stimulated by adenine containing nucleotides and inhibited by millimolar Mg2+ and submicromolar ruthenium red (RR). In addition, analogs of RR, such as hexamminecobalt(III) chloride or hexammineruthenium(III) chloride also inhibit Ca2+ efflux but are effective at somewhat higher concentrations (approximately 50 microM). Calcium release stimulated by phthalocyanines is specific for SR derived from the terminal cisternae region rather than longitudinal SR. Preincubation of alcian blue with the reducing agents, sodium dithionite, dithiothreitol, or cysteine causes complete loss of Ca2+ release activity from SR vesicles. Reoxidation of the alcian blue leads to return of the Ca2+ release activity of the phthalocyanine dye. The copper containing phthalocyanine dyes appear to cause rapid Ca2+ release from SR vesicles by oxidizing sulfhydryl groups associated with the calcium release channel. Moreover, phthalocyanines appear to act by oxidizing a pair of neighboring sulfhydryls to a disulfide because subsequent additions of the reducing agent dithiothreitol promote the closure of the Ca2+ channel and calcium re-uptake.

Alcian Blue↗
PubMed1985

The effect of ferric iron complex on isolated rat liver mitochondria. II. Ion movements.

It has been found that addition of iron(III)-gluconate complex to rat liver mitochondria disturbed the mitochondrial Ca2+ transport. Indirect evidence when the changes in the membrane potential during the transport of Ca2+ were followed, as well as direct evidence, when the fluxes of Ca2+ were monitored by a Ca2+-selective electrode, indicated that this iron complex induced an efflux of Ca2+ from liver mitochondria. The mechanisms by which iron induced Ca2+ release appeared to be linked to the induction of lipoperoxidation of mitochondrial membrane. The mitochondrial membrane, however, did not become irreversibly damaged under these conditions, as indicated by its complete repolarization. It was also shown that the induction by iron of lipoperoxidation brought about an efflux of K+ from mitochondria.

Animals↗
PubMed1978

The effect of sodium on inorganic phosphate- and p-nitrophenyl phosphate-facilitated ouabain binding to (Na+ + K+)-activated ATPase.

The effect of the hydrolysis product Pi and the artificial substrate p-nitrophenyl phosphate (p-nitrophenyl-P) on ouabain binding to (Na+ + K+)-activated ATPase was investigated. The hypothesis that (Mg2+ + p-nitrophenyl-P)-supported ouabain binding might be due to Pi release and thus (Mg2+ + Pi)-supported could not be confirmed. The enzyme . ouabain complexes obtained with different substrates were characterized according to their dissociation rates after removal of the ligands facilitating binding. The character of the enzyme . ouabain complex is determined primarily by the monovalent ion present during ouabain binding, but, qualitatively at least, it is immaterial whether binding was obtained with p-nitrophenyl phosphate or Pi. The presence or absence of Na+ during binding has a special influence upon the character of the enzyme . ouabian complex. Without Na+ and in the presence of Tris ions the complex obtained with (Mg2+ + Pi) and that obtained with (Mg2+ + p-nitrophenyl-P) behaved in a nearly identical manner, both exhibiting a slow decay. High Na+ concentration diminished the level of Pi-supported ouabain binding, having almost no effect on p-nitrophenyl phosphate-supported binding. Both enzyme . ouabain complexes, however, now resembled the form obtained with (Na+ + ATP), as judged from their dissociation rates and the K+ sensitivity of their decay. The complexes obtained at a high Na+ concentration underwent a very fast decay which could be slowed considerably after adding a low concentration of K+ to the resuspension medium. The most stable enzyme . ouabain complex was obtained in the presence of Tris ions only, irrespective of whether p-nitrophenyl phosphate of Pi facilitated complex formation. The presence of K+ gave rise to a complex whose dissociation rate was intermediate between those of the complexes obtained in the presence of Tris and a high Na+ concentration. It is proposed that the different ouabain dissociation rates reflect different reactive states of the enzyme. The resemblance between the observations obtained in phosphorylation and ouabain binding experiments is pointed out.

Adenosine Triphosphatases↗
PubMed1996

The role of efflux systems and the cell envelope in fluorescence changes of the lipophilic cation 2-(4-dimethylaminostyryl)-1-ethylpyridinium in Escherichia coli.

The interaction of the fluorescent dye 2-(4-dimethylaminostyryl)-1-ethlypyridinium cation (DMP+) with cells of Escherichia coli AN120 (uncA) and AS-1 (acrA) was studied to elucidate the role of the envelope and of efflux systems in the uptake of lipophilic cations. DMP+ bound to the two strains in a different manner. With AS-1 the bound dye was displaced only to a small extent by addition of Mg2+ or other divalent cations. By contract, 50% of the DMP+ was displaced by micromolar concentrations of Mg2+ from resting cells of AN120. Energization of the cells by substrate oxidation resulted in the loss in AN120 of 50% of the bound dye and a decrease of the fluorescence in the cell suspension. With AS-1, energization caused more DMP+ to be taken up from the medium. This was associated with an increase in fluorescence in the cell suspension. The extent of the quenching by addition of Mg2+ was not increased. Right-side out vesicles from AN120, like those of AS-1, showed DMP+ fluorescence behaviour which resembled that of intact cells of AS-1. Transformation of AS-1 with plasmids encoding the E. coli Mvr and EmrAB efflux systems resulted in the DMP+ fluorescence response of this strain becoming like that of AN120. It is suggested that with strain AN120 the changes in binding of DMP+ and fluorescence intensity were associated with activation of efflux systems on cell energization. With AS-1, it is suggested that the observed fluorescence and binding changes are due to inactivation of the AcrAB efflux system by the acrA mutation. Thus, the net entry of lipophilic cations is facilitated. Energization of dye update and release is driven by an electrochemical gradient of protons. ATP is not directly involved in energizing the movement of the dye.

Adenosine Triphosphate↗
PubMed1980

The effect of the nitrosourea analog of thymidine, 3'-[3-(2-chloroethyl)-3-nitrosoureido]-3'-deoxythymidine, on Escherichia coli thymidine kinase.

Escherichia coli thymidine kinase (ATP:thymidine 5'-phosphotransferase, EC 2.7.1.21) is irreversibly inactivated by incubation with 3'-[3-(2-chloroethyl)-3-nitrosoureido]-3'-deoxythymidine (3'-CTNU). The inactivation of the enzyme followed first-order kinetics even after loss of 96% of the original activity. This indicates that the inactivation process is a one-kill phenomenon and not a generation of less active enzyme. The addition of a preincubated aqueous solution of 3'-CTNU to the enzyme reaction mixture did not inactivate the enzyme. ATP . Mg2+ but not thymidine protects the enzyme from inactivation by 3'-CTNU. The allosteric regulators, dTTP, dCTP and dCDP also afforded complete protection of the enzyme from inactivation by 3'-CTNU. These data indicate that the dimer form of the enzyme is completely resistant to inactivation by 3'-CTNU, but the monomer form of the enzyme is sensitive. The specificity of the protection is supported by the finding that neither ATP . Mg2+ nor thymidine protect yeast alcohol dehydrogenase from inactivation by this nitrosourea analog of thymidine.

Adenosine Triphosphate↗