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PubMed1989

Protection of hexaprenyl-diphosphate synthase of Micrococcus luteus B-P 26 against inactivation by sulphydryl reagents and arginine-specific reagents.

Hexaprenyl-diphosphate synthase from Micrococcus luteus B-P 26 has been shown to comprise two essential components, designated as components A and B. Treatment of the synthase with sulphydryl reagents (N-ethylmaleimide, iodoacetamide or p-chloromercuribenzoate) or arginine-specific reagents (2,3-butanedione, 1,2-cyclohexanedione or phenylglyoxal) resulted in a rapid loss of the component B activity. In contrast, component A was resistant to treatment with such reagents, retaining the initial activity almost completely. Farnesyl diphosphate, isopentenyl diphosphate, farnesyl monophosphate and inorganic pyrophosphate protected the synthase against the inactivation by N-ethylmaleimide, farnesyl diphosphate being the most effective. The presence of Mg2+ was essential for the protection by isopentenyl diphosphate and inorganic pyrophosphate. For protection of the synthase activity against the inactivation by 2,3-butanedione, the presence of farnesyl diphosphate, isopentenyl diphosphate and Mg2+ was more effective than that of the individual substrates and Mg2+. Inorganic pyrophosphate provided substantial protection. In the absence of component A, the component B activity was not protected by any substrates or its analogue. These results suggest that the catalytic site of the synthase is formed by cooperative interaction between components A and B, and that cysteine and arginine residues on component B play important roles in the synthase activity.

Aldehydes↗
PubMed1991

Vanadate inhibition of ATP and p-nitrophenyl phosphate hydrolysis in the fragmented sarcoplasmic reticulum.

The vanadate inhibition of the Ca(2+)-ATPase activity was analysed both in intact sarcoplasmic reticulum vesicles and in the presence of low concentrations of Tween 20, using ATP and p-nitrophenyl phosphate as substrates. The saturation of the internal low-affinity calcium-binding sites protects the enzyme against vanadate inhibition, because: (1) p-nitrophenyl phosphate hydrolysis is not inhibited by vanadate in intact vesicles, but inhibition developed after solubilization with detergents; (2) the vanadate inhibition of the p-nitrophenyl phosphate hydrolysis in solubilized preparations is prevented by free Ca2+ concentrations higher than 10(-3) M and vanadate competes with calcium (10(-5)-10(-3) M); and (3) the vanadate inhibition of ATP hydrolysis is decreased with an increase in vesicular Ca2+ concentration. The presence of magnesium ions is indispensable for the vanadate effect. The vanadate inhibition is non-competitive with respect to Mg-p-nitrophenyl phosphate and uncompetitive with respect to Mg-ATP. However, in the presence of dimethyl sulfoxide, which facilitates phosphorylation of the enzyme, the inhibition is converted to a competitive one with respect to a substrate. The results suggest, that in the process of enzyme operation vanadate interacts with the unliganded E form of Ca(2+)-ATPase, occupying probably an intermediate position between the E2 and E1 forms, with the formation of an E2 Van complex, that imposes the inhibition on the Ca(2+)-ATPase activity.

4-Nitrophenylphosphatase↗
PubMed1985

Effect of cations and cation channel blockers on human natural killer cells.

We studied the influence of various extracellular Ca++ and Mg++ concentrations on human natural killer (NK) cells and found that NK cell-mediated target cell lysis requires the presence of both divalent cations. The calcium channel blocker verapamil and the local anaesthetics procaine and lidocaine inhibited NK cell-mediated killing of K 562 target cells, whereas the selective K+ channel blocker tetraethylammonium and the selective Na+ channel blocker tetrodotoxin had no effect on NK activity. Our results demonstrate an important role of extracellular Ca++ and Mg++ for NK cell-mediated killing and suggest that a free transmembrane Ca++ passage is required for target cell lysis.

Anesthetics, Local↗
PubMed1991

Intracellular recording of spontaneous activity of canine intracardiac ganglion cells.

Intracellular recordings were made from 302 canine intracardiac ganglion cells with intact synaptic connections. Fifty-two % of these cells exhibited spontaneous membrane potential changes consisting primarily of miniature excitatory postsynaptic potential (EPSP)-like depolarizations upon which an action potential or burst of action potentials was sometimes evoked. Most of the spontaneous potential changes are presumed to be synaptically mediated involving nicotinic mechanisms because they were blocked by low Ca2+/high Mg2+ and hexamethonium solutions.

Action Potentials↗
PubMed1984

Alkaline phosphatases of the mosquito, Culex tarsalis Coquillett.

Spectrophotometric and isoelectric focusing (IEF) electrophoretic characterization of the alkaline phosphatase (ALKP) of the mosquito, Culex tarsalis, are presented. With p-nitrophenylphosphate (Pnp) as substrate, ALKP was optimally active at 37 degrees C, pH 8.0, 30 mM MgCl2, Vmax was 35.8 mumoles/10 min and the Km was 5.7 mM, with no demonstrable requirement for Zn2+. The spectrophotometric enzyme(s) was stimulated by dithiothreitol, 2-mercaptoethanol, and poly-vinylpyrollidone (PVP); inhibited by NaF, several alternative cations (Ca2+, Ba2+, Fe2+, Cu2+), and EDTA. ALKP activity was cyclic during the 15 day post-adult emergence period of the study. No significant differences were noted between the specific activities of males and females. IEF electrophoresis revealed 6 ALKP isozymes detected with alpha-naphthylphosphate within the pH range 4.0-5.5, with a second group of 3 rather indistinct species in the pH 6.0-7.0 range. IEF ALKP isozymes were stimulated by Mg2+ and PVP and inhibited by EDTA (except ALKP5.0) and cysteine; partial inhibition with phenylalanine. IEF detection of ALKP activity with Pnp indicated that the majority of the activity was localized in the pH 4.0-5.5 range, in close agreement with the alpha-naphthylphosphate results.

Alkaline Phosphatase↗
PubMed1996

Cultured airway epithelium responses to mineral particles: role of the oxidative stress.

We tested the hypothesis according to which mineral particles containing iron would be able to produce cytotoxic-ROS. We approached this problem in vitro using primary cultures of rabbit tracheal epithelial cells. The oxidizing power of three mineral particles, i.e. nemalite, chrysotile and hematite, has been evaluated for their capacity to induce lipid peroxidation, and to activate intra-cellular anti-oxidant enzymes. The results show that nemalite and chrysotile which contain Fe2+ have a strong oxidizing power, inducing an oxidative stress on airway epithelial cells, whereas hematite, the Fe3+ containing particles, is without effect.

Animals↗
PubMed2006

Comparison of the TL responses of two different preparations of LiF:Mg,Cu,P irradiated by photons of various energies.

The aim of this work is to present the results concerning the photon irradiation of a new phosphor, the LiF:Mg,Cu,P+PTFE, produced at the Instituto Nacional de Investigaciones Nucleares (ININ-Mexico). The photon irradiations were performed using X-rays of 16, 24, 34.5, 42, 100 and 145keV, and gamma rays from (137)Cs (662keV) and from (60)Co (1 252keV). The results obtained are normalized to the (60)Co response. The experimental data are then compared to those obtained using the commercial dosimeters TLD-100 and GR-200A.

Copper↗
PubMed2006

Trypanosoma brucei brucei: biochemical characterization of ecto-nucleoside triphosphate diphosphohydrolase activities.

In this work we describe the ability of living cells of Trypanosoma brucei brucei to hydrolyze extracellular ATP. In these intact parasites there was a low level of ATP hydrolysis in the absence of any divalent metal (4.72+/-0.51 nmol Pi x 10(-7) cells x h(-1)). The ATP hydrolysis was stimulated by MgCl(2) and the Mg-dependent ecto-ATPase activity was 27.15+/-2.91 nmol Pi x 10(-7) cells x h(-1). This stimulatory activity was also observed when MgCl(2) was replaced by MnCl(2). CaCl(2) and ZnCl(2) were also able to stimulate the ATPase activity, although less than MgCl(2). The apparent K(m) for ATP was 0.61 mM. This ecto-ATPase activity was insensitive to inhibitors of other ATPase and phosphatase activities. To confirm that this Mg-dependent ATPase activity is an ecto-ATPase activity, we used an impermeable inhibitor, DIDS (4, 4'-diisothiocyanostylbene 2'-2'-disulfonic acid), as well as suramin, an antagonist of P(2) purinoreceptors and inhibitor of some ecto-ATPases. These two reagents inhibited the Mg(2+)-dependent ATPase activity in a dose-dependent manner. Living cells sequentially hydrolyzed the ATP molecule generating ADP, AMP and adenosine, and supplementation of the culture medium with ATP was able to sustain the proliferation of T. brucei brucei as well as adenosine supplementation. Furthermore, the E-NTPDase activity of T. brucei brucei is modulated by the availability of purines in the medium. These results indicate that this surface enzyme may play a role in the salvage of purines from the extracellular medium in T. brucei brucei.

4,4'-Diisothiocyanostilbene-2,2'-Disulfonic Acid↗
PubMed2006

Protein phosphorylation and membrane association of sucrose synthase in developing tomato fruit.

Calcium-dependent protein kinase (CDPK) activities were detected both in the soluble and the membrane fraction of various tomato (Lycopersicon esculentum Mill.) organs, using a synthetic peptide mimicking the serine 11 phosphorylation site of a tomato sucrose synthase (SS, EC 2.4.1.13) isoform as substrate. The levels of membrane and soluble Ser-CDPK activities were differentially regulated during fruit development. The membrane Ser-CDPK activity was maximal in young fruit but decreased as the fruit developed, suggesting a specific role during fruit growth. Using an in gel assay with purified tomato SS as substrate, we showed that partially purified soluble and membrane Ser-CDPK preparations both contained a SS-kinase polypeptide of 55 kDa. The membrane and soluble Ser-CDPK activities were largely inactivated in the absence of calcium or when MgCl(2) was replaced by MnCl(2). Both soluble and membrane Ser-CDPK activities were very sensitive to staurosporine. Using Fe(III)-immobilized metal chromatography to determine the apparent phosphorylation status of the enzyme in vivo, we showed that soluble SS was largely dephosphorylated in fruits fed EGTA or staurosporine, compared to fruits fed water or sucrose. Moreover, the level of SS increased by about two-fold in the membrane fraction of fruits fed the Ser-CDPK inhibitors, compared to the control. The level of SS protein in the membrane and soluble fractions of tomato fruit was developmentally regulated, the membrane form being specifically detected in actively growing fruits. Together, our results suggest that a mechanism involving protein phosphorylation/dephosphorylation and/or calcium would in part control the association of SS isoforms with membranes in developing tomato fruit.

Calcium↗
PubMed1988

Elucidation of the 2-aminoethylphosphonate biosynthetic pathway in Tetrahymena pyriformis.

The biosynthetic reaction pathway leading to the natural product, 2-aminoethylphosphonate in Tetrahymena pyriformis has been elucidated. Incubation of [32P]PEP and [14C]PEP with T.pyriformis cellular homogenate fortified with Mg2+ and alanine/pyridoxal phosphate, yielded 2-aminoethylphosphonate as the minor reaction product (2-5% yield) and phosphoglycerate and pyruvate plus orthophosphate as the major products. Inclusion of thiamine pyrophosphate in the reaction mixture increased the yield of 2-aminoethylphosphonate by a factor of 10. Incubation of phosphonoacetaldehyde or phosphonopyruvate in the cellular homogenate also provided 2-aminoethylphosphonate. The cellular homogenate catalyzed the transformation of phosphonoacetaldehyde to 2-aminoethylphosphonate in an ca. 80% yield. However, the maximum yield of 2-aminoethylphosphonic acid obtained by use of phosphonopyruvate was only 15%. The major reaction pathways induced by treatment of phosphonopyruvate with the cellular extract involved its competitive conversion to PEP and pyruvate plus orthophosphate.

Acetaldehyde↗
PubMed1979

Arsenazo III forms 2:1 complexes with Ca and 1:1 complexes with Mg under physiological conditions. Estimates of the apparent dissociation constants.

Experiments to determine the apparent dissociation constants of the Ca and Mg complexes of arsenazo III clearly indicated that the predominant Ca complex contains one Ca ion and two dye molecules, although previous reports have either claimed or assumed 1:1 complexing. The evidence is based on the effects of varying [dye] as well as [Ca] and [Mg], and clear evidence for the formation of 1:1 complexes with Ca was obtained only at submicromolar [dye], whereas Mg formed 1:1 complexes exclusively. The implications of these findings with regard to the use of arsenazo III as an indicator of intracellular free [Ca] are discussed, with particular reference to its selectivity for Ca and the interference effects of other ions.

Arsenazo III↗
PubMed1994

Condensation of supercoiled DNA induced by MnCl2.

Multivalent cations condense DNA in vitro, but it had been thought that a valence of at least + 3 was required in aqueous solution. We have found that Mn2+ can produce toroidal condensates of supercoiled plasmid DNA, but not of linearized plasmid. Mg2+ does not cause condensation, and neither MgCl2 nor NaCl can negate the effect of MnCl2, indicating that the condensation mechanism with Mn is not primarily electrostatic. Supercoiled MnDNA is more extensively digested than the linear form by S1 nuclease. Supercoiling appears to cooperate with Mn2+ in stabilizing helix distortions and also provides a "pressure" that enhances lateral association.

Chlorides↗
PubMed1992

Effects of the N-methyl-D-aspartate antagonists on the rise in [Ca2+]i following depolarization in aged rat brain synaptosomes.

The effects of non-competitive NMDA antagonists, MK-801 and dextrorphan in relation to the rise in intracellular Ca2+ concentrations ([Ca2+]i) after stimulation with 15 mM K+ in whole brain synaptosomes from young (3 months old) and aged (24 months old) Fisher344 rats were examined. A fluorescent chelating agent, Rhod-2, was employed to monitor any alterations of K(+)-evoked [Ca2+]i. In young rats, the rise in [Ca2+]i following depolarization was affected by neither dextrorphan (1, 10, 100 microM) nor MK-801 (0.1, 1, 10 microM), while in aged rats, 1 microM dextrorphan and 0.1 microM MK-801 brought about a significant increase in [Ca2+]i following depolarization. In low Mg2+ medium, 10 microM MK-801 and 100 microM dextrorphan significantly inhibited the rise in [Ca2+]i after stimulation with 15 mM K+ in young rats, while neither dextrorphan nor MK-801 could affect the rise in [Ca2+]i significantly in aged rats. When 100 microM NMDA was applied in a medium containing 1.2 mM Mg2+, the rise in [Ca2+]i following depolarization was slightly inhibited by 1 microM MK-801 in young rats, but it was not inhibited significantly by dextrorphan. In aged rats, both 100 microM dextrorphan and 10 microM MK-801 strongly inhibited the rise in [Ca2+]i following depolarization in the presence of 100 microM NMDA. Instead of NMDA, when 100 microM alpha-amino-3-hydroxy-5-methyl-4-isoxazolepropionic acid (AMPA), a non-NMDA receptor agonist, was applied, dextrorphan did not inhibit the rise in [Ca2+]i. In low Mg2+ medium, 100 microM NMDA potentiated the inhibitory effect of 10 microM dextrorphan in young rats, while 100 microM dextrorphan or MK-801 did not show any further inhibition by adding 100 microM NMDA. The addition of 100 microM AMPA did not affect the effect of dextrorphan in a low Mg2+ medium in young rats. These results suggest that NMDA antagonist-mediated [Ca2+]i homeostatic system may alter through aging. In addition, the findings that NMDA potentiated the inhibitory effect of NMDA antagonist, which being further potentiated by aging or lowered extrasynaptosomal Mg2+, indicate the possibility that the Mg2+ block to NMDA receptors might be attenuated through aging.

Aging↗