Search PubMed⌕ Search

SEARCH · Search PubMed

Results for “Cations, Divalent”

Search indexed PubMed citations on genomics, clinical trials, systematic reviews and public health. Explore titles, authors and supplied subject terms, then open the PubMed record.

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

At least 1,045 records · Page 58Linked to original sources
PubMed2001

Divalent cation interactions with oligogalacturonides.

The conformational properties of high and low molecular weight galacturonides were investigated in relation to the ability of oligomers with degree of polymerization >10 to act as elicitors of plant defense mechanisms. Oligomers from polygalacturonate were obtained by means of enzymatic hydrolysis. Two fractions exhibiting high and low average degrees of polymerization were isolated by solvent fractionation and characterized by means of electrospray mass spectrometry. The conformational behaviors of the two fractions were investigated in the presence of different divalent cations using circular dichroism. Calcium, copper, and zinc ions were able to induce a conformational transition in both fractions. When in the presence of the high molecular weight fraction, copper and zinc ions were much more effective than calcium ions, whereas the efficiency was much reduced with low molecular weight oligomers.

Cations, Divalent↗
PubMed1992

Divalent cation and prenyl pyrophosphate specificities of the protein farnesyltransferase from rat brain, a zinc metalloenzyme.

The separate catalytic roles of Zn2+ and Mg2+ and the specificity of the prenyl pyrophosphate-binding site of the rat brain protein farnesyltransferase were explored using a purified enzyme preparation. The binding of p21Hras to the enzyme was abolished by dialysis against EDTA and restored by addition of ZnCl2, as demonstrated by chemical cross-linking. The binding of the other substrate, farnesyl pyrophosphate, was independent of divalent cations, as demonstrated by gel filtration. Transfer of the enzyme-bound farnesyl group to the bound p21Hras required Mg2+. Geranylgeranyl pyrophosphate bound to the prenyl pyrophosphate-binding site with an affinity equal to that of farnesyl pyrophosphate, but the geranylgeranyl group was not transferred efficiently to p21Hras. It also was not transferred to a modified p21Hras containing COOH-terminal leucine, a protein that was shown previously to be a good substrate for a rat brain geranylgeranyltransferase. We conclude that the protein farnesyltransferase is a metalloenzyme that most likely contains Zn2+ at the peptide-binding site. It thus resembles certain metallopeptidases, including carboxypeptidase A and the angiotensin-converting enzyme. Strategies previously developed to screen for inhibitors of those enzymes may aid in the search for inhibitors of the protein farnesyltransferase.

Alkyl and Aryl Transferases↗
PubMed2001

Divalent cations in women with PCOS: implications for cardiovascular disease.

Polycystic ovary syndrome (PCOS) patients are known to have a high incidence of insulin resistance and glucose intolerance and tend to be at eventual high risk of hypertension, diabetes mellitus and cardiovascular disease. It has been repeatedly shown that a low serum ionized magnesium (Mg2+) and a high ionized calcium to magnesium (Ca2+/Mg2+) ratio is often associated with insulin resistance, cardiovascular problems, diabetes mellitus and hypertension. We were therefore interested in assessing the serum divalent cation profile of PCOS patients compared with that of normal women of similar age. We found significantly lower serum Mg2+ and total magnesium and a significantly higher serum Ca2+/Mg2+ ratio in the PCOS patients compared with the controls. No correlation was found, however, between the serum concentrations of steroid hormones (estrogen, progesterone and testosterone), or any of the cations in the PCOS patients or the controls.

Adult↗
PubMed1998

Tissue inhibitor of metalloproteinase-2 protection of matrix metalloproteinase-2 from degradation by plasmin is reversed by divalent cation chelator EDTA and the bisphosphonate alendronate.

The degradation of tissue inhibitor of metalloproteinase (TIMP)-free matrix metalloproteinase (MMP)-2 to proteolytically inactive fragments by plasmin was inhibited in equimolar mixtures of purified TIMP-2 and TIMP-free MMP-2 and was not observed in purified MMP-2-TIMP-2 complexes. Divalent cation chelators EDTA and sodium Alendronate did not inhibit plasmin degradation of TIMP-free MMP-2 but reversed the ability of TIMP-2 to protect MMP-2 from degradation by plasmin. Our data confirm a role for plasmin in the clearance of TIMP-free MMP-2, identify a pivotal role for TIMP-2 in regulating MMP-2 longevity in plasmin-containing environments, and highlight a novel therapeutic use for chelators of divalent cations, including the bisphosphonate Alendronate, in the reversal of TIMP-2 protection of MMP-2 from degradation by plasmin. We propose that these observations are relevant to pathologies that are dependent upon plasmin and MMP-2 activity (e.g., tumor invasion and metastasis).

Alendronate↗
PubMed1998

Regulation of agonist-receptor binding by G proteins and divalent cations in spermatozoa solubilized A1 adenosine receptors.

Solubilized A1 adenosine receptor (A1AR) was used to investigate the effect of several cations on agonist-binding characteristics and GTP hydrolysis. It was shown by Western blot with G beta-M14 that this preparation contains both G proteins and receptor. The role of the receptor molecule is to facilitate the activation of G proteins as alpha-GTP complex, and GTP hydrolysis has important consequences for the basic deactivation mechanism. Divalent cations, such as Mn2+, Ca2+, and Mg2+, potentiated the agonist-specific binding: Mn2+ had the highest apparent affinity with half-maximal effect at 50 microM. Binding assays, performed in the presence of 100 microM Mn2+, showed an increase in the apparent affinity of the binding sites, whereas, in the presence of 1 mM Mg2+, significant alteration of the apparent affinity, but not of the number of sites, was detected. Concentrations of 1 mM Mg2+ and 100 microM Mn2+ enhanced GTPase activity, whereas 5 mM Ca2+ resulted in the increase of Vmax values without significant alterations of K(m). In the presence of A1-specific agonists, Mn2+ and Mg2+ caused a decrease of Vmax values and an increase of GTP affinity. Other cations, such as Co2+, Cd2+, Cu2+, and Zn2+, inhibited the binding capacity but caused almost no changes in GTP hydrolysis kinetics.

Animals↗
PubMed1994

Crystal structures of synthetic 7 angstrom and 10 angstrom manganates substituted by mono- and divalent cations.

The crystal structures of synthetic 7 angstrom and 10 angstrom manganates, synthetic birnessite and buserite, substituted by mono- and divalent cations were investigated by X-ray and electron diffractions. The monoclinic unit cell parameters of the subcell of lithium 7 angstrom manganate, which is one of the best ordered manganates, were obtained by computing the X-ray powder diffraction data: a = 5.152 angstroms, b = 2.845 angstroms, c = 7.196 angstroms, beta = 103.08 degrees. On the basis of the indices obtained by computing the X-ray diffraction data of Li 7 angstrom manganate, monovalent Na, K and Cs and divalent Be, Sr and Ba 7 angstrom manganates were interpreted as the same monoclinic structure with beta = 100-103 degrees as that of Li 7 angstrom manganate, from their X-ray diffraction data. In addition, divalent Mg, Ca and Ni 10 angstrom manganates were also interpreted as the same monoclinic crystal system with beta=90-94 degrees. The unit cell parameters, especially a, c and beta change possibly with the type of substituent cation probably because of the different ionic radius, hydration energy and molar ratio of substituent cation to manganese. However, these diffraction data, except for those of Sr and Ba 7 angstrom and Ca and Ni 10 angstrom manganates, reveal only some parts of the host manganese structure with the edge-shared [MnO6] octahedral layer. On the other hand, one of the superlattice reflections observed in the electron diffractions was found in the X-ray diffraction lines for heavier divalent cations Sr and Ba 7 angstrom and Ca and Ni 10 angtrom manganates. The reflection presumably results from the substituent cation position in the interlayer which is associated with the vacancies in the edge-shared [MnO6] layer and indicates that the essential vacancies are linearly arranged parallel to the b-axis. Furthermore, the characteristic superlattice reflection patterns for several cations, Li, Mg, Ca, Sr, Ba and Ni, manganates were interpreted that the substituent cations are regularly distributed in the interlayer according to the exchange percentage of substituent cation to Na+. In contrast, the streaking in the a-direction observed strongly in the electron diffractions for heavier monovalent cations, K and Cs, manganates probably results from the disordering of their cations in the a-direction in the interlayer.

Cations↗
PubMed1991

Proteoglycans of bovine articular cartilage. The effects of divalent cations on the biochemical properties of link protein.

In cartilage proteoglycan aggregates, link protein stabilizes the binding of proteoglycan monomers to hyaluronate by binding simultaneously to hyaluronate and to the G1 globular domain of proteoglycan monomer core protein. Studies reported here involving metal chelate affinity chromatography demonstrate that link protein is a metalloprotein that binds Zn2+, Ni2+, and Co2+. Zn2+ and Ni2+ decrease the solubility of link protein and result in its precipitation. However, link protein is readily soluble and functional in low ionic strength solvents from which divalent cations have been removed with Chelex 100. These observations make it possible to study the biochemical properties of link protein in low ionic strength, physiologic solvents. Studies were carried out to define the oligomeric state of link protein alone in physiologic solvents, and the transformation in oligomeric state that occurs when link protein binds hyaluronate. Sedimentation equilibrium studies demonstrate that in 0.15 M NaCl, 5 mM EDTA, 50 mM Tris, pH 7, link protein exists as a monomer-hexamer equilibrium controlled by a formation constant of 2 x 10(27) M-5, yielding a delta G' of -36 kcal/mol for the formation of the hexamer from six monomers. On binding hyaluronate oligosaccharides (HA10 or HA12), link protein dissociates to dimer. Link protein hexamer is rendered insoluble by Zn2+. Greater than 90% of the protein is precipitated by 2 mol of Zn2+/mol of link protein monomer. The binding of hyaluronate oligosaccharide by link protein strongly inhibits the precipitation of link protein by Zn2+. The link protein/hyaluronate oligosaccharide complex is completely soluble in the presence of 2 mol of Zn2+/mol of link protein. At higher molar ratios of Zn2+/link protein, the inhibitory effect of hyaluronate oligosaccharide on the precipitation of link protein is gradually overcome. Hyaluronate oligosaccharide is not dissociated from link protein by Zn2+. Hyaluronate remains bound to the link protein which is precipitated by Zn2+, or to the link protein which binds to Zn2(+)-charged iminodiacetate-Sepharose columns. Hyaluronate oligosaccharides and Zn2+ bind to different sites on link protein.

Animals↗
PubMed2000

Divalent cation transport by the distal nephron: insights from Bartter's and Gitelman's syndromes.

Elucidation of the gene defects responsible for many disorders of renal fluid and electrolyte homeostasis has provided new insights into normal and abnormal physiology. Identifying the causes of Gitelman's and Bartter's syndromes has greatly enhanced our understanding of ion transport by thick ascending limb and distal convoluted tubule cells. Despite this information, several phenotypic features of these diseases remain confusing, even in the face of molecular insight. Paramount among these are disorders of divalent cation homeostasis. Bartter's syndrome is caused by dysfunction of thick ascending limb cells. It is associated with calcium wasting, but magnesium wasting is usually mild. Loop diuretics, which inhibit ion transport by thick ascending limb cells, markedly increase urinary excretion of both calcium and magnesium. In contrast, Gitelman's syndrome is caused by dysfunction of the distal convoluted tubule. Hypocalciuria and hypomagnesemia are universal parts of this disorder. Yet although thiazide diuretics, which inhibit ion transport by distal convoluted tubule cells, reduce urinary calcium excretion, they have minimal effects on urinary magnesium excretion, when given acutely. This review proposes mechanisms that may account for the differences between the effects of diuretic drugs and the phenotypic features of Gitelman's and Bartter's syndromes. These mechanisms are based on recent insights from another inherited disease of ion transport, inherited magnesium wasting, and from a review of the chronic effects of diuretic drugs in animals and people.

Animals↗
PubMed1993

Interactions between forskolin, GS, and divalent cations on ciliary process adenylyl cyclase and intraocular pressure in the rabbit eye.

The major adenylyl cyclase activity (AC) of rabbit ocular ciliary processes was investigated by dose-response analysis with respect to interactions of its regulators [the stimulatory G-protein (alpha S) and forskolin] under both saturating and suboptimal divalent cation (M2+) conditions. alpha S was generated directly with fluoroaluminate or via receptors for vasoactive intestinal peptide or isoproterenol. Forskolin and alpha S when liganded simultaneously to AC at suboptimal M2+, potentiated maximal enzyme activity (approximately twice the sum of the separate activities), while the responses were additive (no potentiation) under saturating M2+ conditions. The results demonstrate that the three ligands (forskolin, M2+ and alpha S) mutually interact in a cooperative manner as follows: (1) The apparent k(act) of forskolin for AC was decreased by 1.7-1.9 log units when alpha S was liganded to AC. (2) Conversely, with forskolin liganded to AC the apparent k(act) of alpha S for AC also decreased by a factor of at least 3-4. (3) The nature of the divalent cation M2+ had no effect on the k(act) of alpha S for AC alone and for the AC:FSK complex, and also did not affect the apparent k(act) of forskolin for AC alone, or for the AC: alpha S complex. The nature of M2+ (Mg2+ or Mn2+) affected only the maximal catalytic rate (Emax). (4) Potentiation of adenylyl cyclase by alpha S + FSK was demonstrable in vivo by the increased ocular pressure response of the rabbit eye when a low topical dose of isoproterenol (125 ng per eye) and a subthreshold dose of forskolin (100 micrograms per eye) were given in combination.

Adenylyl Cyclases↗
PubMed1982

Effects of divalent cations, trypsin, and phospholipases on the passive permeability to sodium of inside-out vesicles from human red cells.

Inside-out vesicles (IOV) were prepared from human red blood cells. Steady-state uptake of 23Na was observed to generally follow an exponential time course with a rate constant of 1.57 +/- 0.09 h-1 (SE). One week of cold storage (0-4 degrees C) increased the rate constant to 2.50 +/- 0.12 h-1 (SE). Mg2+, Ca2+, or Sr2+ decreased the rate of 22Na uptake with no observable differences between the three divalent cations when tested at concentrations of 50 microM. Mg2+ was shown to decrease the rate of 22Na uptake at concentrations as low as 5 microM with maximal effect at 50 to 100 microM. The decrease in rate of 22Na uptake induced by Mg2+ could be enhanced by exposure of IOV to Mg2+ for longer periods of time. Trypsin treatment of OIV increased the rate of uptake of 22Na and was dependent on the concentration of trypsin added between 5 to 25 micrograms/ml (treated for 5 min at 25 degrees C). The ability of Mg2+ (50 microM) to decrease the rate of 22Na uptake was still observed after maximal trypsin treatment. Phospholipase A2 or phospholipase C treatment of IOV increased the rate of 22Na uptake and was dependent on the amount of phospholipase A2 (0.1 to 1.0 units/ml) or phospholipase C (0.25 to 2.5 units/ml) added (treated for 5 min at 25 degrees C). After phospholipase A2 treatment, the observed decrease in the rate of 22Na uptake induced by Mg2+ (50 microM) was generally greater than controls. After phospholipase C treatment, the observed decrease in rate of 22Na uptake induced by Mg2+ (50 microM) was less or absent when compared with controls. Phospholipase C treatment was less effective in preventing the Mg2+ effect the longer IOV were exposed to Mg2+. The results suggest that Mg2+ binds to phospholipid headgroups to reduce Na permeability perhaps by inducing a change in bilayer structure or phospholipid association.

Cations, Divalent↗
PubMed1979

Conditions limiting the use of ionophore A23187 as a probe of divalent cation involvement in biological reactions. Evidence from the slow fluorescence quenching of type A spinach chloroplasts.

The conditions under which ionophore A23187 can be used as a probe of Mg2+ involvement in the reactions of intact (Type A) spinach chloroplasts have been investigated by monitoring ionophore-induced reversal of slow fluorescence quenching. The following observations were made: (1) A23187-dependent reversal of quenching is a strong function of pH. This is consistent with competition between protons and divalent cations for the carboxylic acid moiety of the ionophore. (2) In the presence of exogenous Mg2+, quenching reversal by A23187 is significantly slowed. It is suggested that formation of the dimeric A23187 . Mg2+ complex delays action of the ionophore at the thylakoid membrane by slowing equilibration of the ionophore among chloroplast membrane phases. (3) In the absence of Mg2+, significant interaction of A23187 with certain monovalent cations--Li+ and Na+, but not K+--is observed. Evaluations of the interaction of ionophore A23187 with specific biological systems and inferences of divalent cation involvement, or lack thereof, must take these limitations into account.

Anti-Bacterial Agents↗
PubMed1977

The effect of atebrin on bacterial membrane adenosine triphosphatases in relation to the divalent cation used as substrate and/or activator.

The action of atebrin on purified adenosine triphosphatase (ATPase) from Micrococcus lysodeikticus was studied as well as on the membrane-bound and soluble ATPases from Escherichia coli and Bacillus megaterium. Atebrin inhibited the Ca(2+)-dependent activity of all these enzymes, and the inhibition was reversed by an excess of Ca(2+) ions. Kinetic studies carried out with the purified enzyme from M. lysodeikticus showed that the inhibition by atebrin was strongly cooperative, suggesting the complex nature of the process. On the other hand, atebrin stimulated the Mg(2+)ATPase activity of the M. lysodeikticus enzyme, displacing its adenosine 5'-triphosphate (ATP)/Mg(2+) optimum ratios, but inhibited the Mg(2+)-ATPase activity of E. coli provided that ATP was in excess over Mg(2+), i.e., that the ATP/Mg(2+) ratio was higher than its optimum. These results suggest that divalent cations influence the bacterial ATPases in different ways depending on the type of divalent ion and/or enzyme. The effect of atebrin on bacterial ATPases may reflect those differences, and its complex mechanism of action might be related to the existence of more than one site for divalent cations and/or distinct conformational states in these enzymes.

Adenosine Triphosphatases↗
PubMed1990

Effects of manganese and other divalent cations on progressive motility of human sperm.

Manganese (Mn2+) stimulated the progressive motility of human washed sperm in a time- and dose-dependent manner. This confirmed previous data indicating a capacity for activating the adenylyl cyclase of sperm homogenates in vitro. A maintained response was best seen with doses 0.2-1.0 mM. After an initial stimulation, higher concentrations of up to 20 mM were associated with a decline in the response to control levels. Magnesium ions (Mg2+) stimulated motility in the same dose range but to less than 50% of the Mn2+ response. Other divalent cations such as zinc (Zn2+), strontium (Sr2+), and Calcium (Ca2+) also exerted stimulatory effects to varying degrees in descending order. Metal ion effects on sperm motility may be mediated through a common cation-binding site on the adenylyl cyclase.

Cations, Divalent↗
PubMed1999

Sr2+ induce a release of divalent cation from internal Ca2+ store by nerve stimulation at frog neuromuscular junction.

The effects of Sr2+ on the transmitter release at the frog neuromuscular junction were examined electrophysiologically. The nerve trunk was stimulated by paired pulses at various time intervals after replacing extracellular Ca2+ by Sr2+, the paired-pulse facilitation at the 10 ms interval was smaller than that at 20-30 ms intervals. Administration of several intracellular Ca2+ mobilizers decreased the paired-pulse facilitation. These results suggest that the transmitter release in Sr2+ solution is caused, at least partly, by the release of divalent cations from the intracellular stores.

Animals↗
PubMed1996

Inhibition of trichocyst exocytosis and calcium influx in Paramecium by amiloride and divalent cations.

Regulated exocytosis of defensive secretory organelles, the trichocysts, as well as a transient Ca(2+)-influx can be induced in Paramecium by aminoethyldextran (Kerboeuf and Cohen, J Cell Biol (1990) 111, 2527). Knoll et al (Febs Lett (1992) 304, 265) reported that veratridine was also a secretagogue for Paramecium. Here we show that, like aminoethyldextran, veratridine induces a transient Ca(2+)-influx. Both aminoethyldextran- and veratridine-induced exocytosis and associated Ca(2+)-influx were: i) blocked in the ndl2 thermosensitive mutant at the non-permissive temperature; and ii) inhibited by amiloride and four divalent cations, Ba2+, Mg2+, Sr2+ and Co2+. This suggests that, although of different chemical nature, aminoethyldextran and veratridine act through the same physiological pathway. In addition, the inhibitory doses are comparable to the ones found to inhibit a hyperpolarization-sensitive Ca(2+)-current described in Paramecium (Preston et al (1992) J Gen Physiol 100, 233). The possibility that the activation of this Ca(2+)-current by the secretagogue represents an early step in the regulation of trichocyst exocytosis is discussed.

Amiloride↗
PubMed1998

The rubella virus nonstructural protease requires divalent cations for activity and functions in trans.

The rubella virus (RUB) nonstructural (NS) protease is a papain-like cysteine protease (PCP) located in the NS-protein open reading frame (NSP-ORF) that cleaves the NSP-ORF translation product at a single site to produce two products, P150 (the N-terminal product) and P90 (the C-terminal product). The RUB NS protease was found not to function following translation in vitro in a standard rabbit reticulocyte lysate system, although all of the other viral PCPs do so. However, in the presence of divalent cations such as Zn2+, Cd2+, and Co2+, the RUB NS protease functioned efficiently, indicating that these cations are required either as direct cofactors in catalytic activity or for correct acquisition of three-dimensional conformation of the protease. Since other viral and cell PCPs do not require cations for activity and the RUB NS protease contains a putative zinc binding motif, the latter possibility is more likely. Previous in vivo expression studies of the RUB NS protease failed to demonstrate trans cleavage activity (J.-P. Chen et al., J. Virol. 70:4707-4713, 1996). To study whether trans cleavage could be detected in vitro, a protease catalytic site mutant and a mutant in which the C-terminal 31 amino acids of P90 were deleted were independently introduced into plasmid constructs that express the complete NSP-ORF. Cotranslation of these mutants in vitro yielded both the native and the mutated forms of P90, indicating that the protease present in the mutated construct cleaved the catalytic-site mutant precursor. Thus, RUB NS protease can function in trans.

Cadmium↗
PubMed2001

Marked activation of the N-acylphosphatidylethanolamine-hydrolyzing phosphodiesterase by divalent cations.

N-Acylethanolamines including anandamide (an endogenous ligand for cannabinoid receptors) are released from N-acylphosphatidylethanolamine (N-acyl-PE) by the catalysis of a phosphodiesterase of the phospholipase D type. The enzyme was solubilized from the particulate fractions of rat heart with the aid of octyl glucoside, and partially purified by anion-exchange chromatography. The enzyme hydrolyzed N-palmitoyl-PE with a specific activity of 17 nmol/min/mg protein at 37 degrees C. The enzyme activity increased dramatically up to 30-fold by millimolar order of Ca(2+). Ca(2+) could be replaced with other divalent cations such as Co(2+), Mg(2+), Mn(2+), Ba(2+), Sr(2+) and Ni(2+). The hydrolysis of N-arachidonoyl-PE (a precursor of anandamide) was also markedly stimulated by Ca(2+).

Animals↗
PubMed1980

Role of calcium in exocrine pancreatic secreation. VI. Characteristics of the paracellular pathway for divalent cations.

(1) The transepithelial permeability for Ca2+ and Mg2+ in the isolated rabbit pancreas has been studied. (2) Values for the permeability of the unstimulated pancreas were obtained either by adding radioactive tracers to the bathing medium and measuring their concentration in the secreted fluid under steady-state conditions, or by analysis of the Ca2+ and Mg2+ concentrations in the secreted fluid after correction for protein-bound divalent cations. (3) Both methods give almost the same results: 27 and 26% for Ca2+ and 21 and 18% for Mg2+, respectively; both values being expressed as the percentage of the concentrations in the bathing medium. (4) The amounts of Ca2+ and Mg2+, appearing in the secretory fluid after correction for protein-bound cations, are linearly related to the extracellular Ca2+ and Mg2+ concentrations in the bathing medium, which indicates passive permeation. The two cations appear to pass through the paracellular route in their hydrated form. (5) Stimulation with carbachol or pancreozymin causes an increase in the paracellular permeability. This increase is approximately equal for the two divalent cations. Its time dependence and magnitude depend on the concentration of the stimulant rather than on the type of stimulant.

Animals↗