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Ca2+ Ions (ca2+ + ion)
Selected AbstractsTemperature and Ca2+ ion as modulators in cellular immunity of the Sunn pest Eurygaster integriceps Puton (Heteroptera: Scutelleridae)ENTOMOLOGICAL RESEARCH, Issue 6 2009Arash ZIBAEE Abstract Environmental conditions in addition to divalent cations may affect the interactions between pathogens and insects. Elucidation of factors which modulate insect immune responses could be a significant part of investigations in this area. In this study, adults of Eurygaster integriceps, as the destructive pest of wheat, were kept at different temperatures in addition to injection with different concentrations of Ca2+ to find the effect on cellular immune reactions against Beauveria bassiana. Results showed that total and differentiate hemocyte numbers, nodule formation and phenoloxidase activity increased with elevation of temperature so that the higher values were obtained at 30 and 40°C at various intervals. Higher concentrations of Ca2+ ion (5 mM) caused an increase in plasmatocyte length and width especially after 60 min. Similar results were observed for nodule formation and phenoloxidase activity of E. integriceps adults after injection by B. bassiana spores and phenoloxidase activity. It is clear from the current study that thermoregulation and Ca2+ ion can positively affect the hemocyte numbers especially plasmatocytes and granulocytes, nodule formation and phenoloxidase activity in E. integriceps. The understanding of modulators of the insect immune response may directly influence novel approaches to obtain safe and effective biological control agents. [source] Molecular cloning, genomic organization and functional characterization of a new short-chain potassium channel toxin-like peptide BmTxKS4 from Buthus martensii Karsch(BmK)JOURNAL OF BIOCHEMICAL AND MOLECULAR TOXICOLOGY, Issue 4 2004Sheng Jiqun Abstract Scorpion venom contains many small polypeptide toxins, which can modulate Na+, K+, Cl,, and Ca2+ ion,channel conductance in the cell membrane. A full-length cDNA sequence encoding a novel type of K+ -channel toxin (named BmTxKS4) was first isolated and identified from a venom gland cDNA library of Buthus martensii Karsch (BmK). The encoded precursor contains 78 amino acid residues including a putative signal peptide of 21 residues, propeptide of 11 residues, and a mature peptide of 43 residues with three disulfide bridges. BmTxKS4 shares the identical organization of disulfide bridges with all the other short-chain K+ -channel scorpion toxins. By PCR amplification of the genomic region encoding BmTxKS4, it was shown that BmTxKS4 composed of two exons is disrupted by an intron of 87 bp inserted between the first and the second codes of Phe (F) in the encoding signal peptide region, which is completely identical with that of the characterized scorpion K+ -channel ligands in the size, position, consensus junctions, putative branch point, and A+T content. The GST-BmTxKS4 fusion protein was successfully expressed in BL21 (DE3) and purified with affinity chromatography. About 2.5 mg purified recombinant BmTxKS4 (rBmTxKS4) protein was obtained by treating GST-BmTxKS4 with enterokinase and sephadex chromatography from 1 L bacterial culture. The electrophysiological activity of 1.0,M rBmTxKS4 was measured and compared by whole cell patch-clamp technique. The results indicated that rBmTxKS4 reversibly inhibited the transient outward K+ current (Ito), delayed inward rectifier K+ current (Ik1), and prolonged the action potential duration of ventricular myocyte, but it has no effect on the action potential amplitude. Taken together, BmTxKS4 is a novel subfamily member of short-strain K+ -channel scorpion toxin. © 2004 Wiley Periodicals, Inc. J Biochem Mol Toxicol 18:187,195, 2004; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/jbt.20026 [source] Temperature dependence of structure and dynamics of the hydrated Ca2+ ion according to ab initio quantum mechanical charge field and classical molecular dynamicsJOURNAL OF COMPUTATIONAL CHEMISTRY, Issue 6 2010Len Herald V. Lim Abstract Simulations using ab initio quantum mechanical charge field molecular dynamics (QMCF MD) and classical molecular dynamics using two-body and three-body potentials were performed to investigate the hydration of the Ca2+ ion at different temperatures. Results from the simulations demonstrate significant effects of temperature on solution dynamics and the corresponding composition and structure of hydrated Ca2+. Substantial increase in ligand exchange events was observed in going from 273.15 K to 368.15 K, resulting in a redistribution of coordination numbers to lower values. The effect of temperature is also visible in a red-shift of the ion-oxygen stretching frequencies, reflecting weakened ligand binding. Even the moderate increase from ambient to body temperature leads to significant changes in the properties of Ca2+ in aqueous environment. © 2009 Wiley Periodicals, Inc. J Comput Chem, 2010 [source] The molecular mechanism of human group IIA phospholipase A2 inactivation by bolinaquinoneJOURNAL OF MOLECULAR RECOGNITION, Issue 6 2009Maria Chiara Monti Abstract The molecular basis of the human group IIA secretory phospholipase A2 inactivation by bolinaquinone (BLQ), a hydroxyquinone marine terpenoid, has been investigated for the comprehension of its relevant antiinflammatory properties, through the combination of spectroscopic techniques, biosensors analysis, mass spectrometry (MS) and molecular docking. Indeed, sPLA2s are well known to be implicated in the pathogenesis of inflammation such as rheumatoid arthritis, septic shock, psoriasis and asthma. Our results suggest a mechanism of competitive inhibition guided by a non-covalent molecular recognition event, disclosing the key role of the BLQ hydroxyl-quinone moiety in the chelation of the catalytic Ca2+ ion inside the enzyme active site. The understanding of the sPLA2 -IIA inactivation mechanism by BLQ could be useful for the development of a new chemical class of PLA2 inhibitors, able to specifically target the enzyme active site. Copyright © 2009 John Wiley & Sons, Ltd. [source] Ca2+ -dependent components of inactivation of unitary cardiac L-type Ca2+ channelsTHE JOURNAL OF PHYSIOLOGY, Issue 1 2010Ira R. Josephson A Ca2+ ion-dependent inactivation (CDI) of L-type Ca2+ channels (LCC) is vital in limiting and shaping local Ca2+ ion signalling in a variety of excitable cell types. However, under physiological conditions the unitary LCC properties that underlie macroscopic inactivation are unclear. Towards this end, we have probed the gating kinetics of individual cardiac LCCs recorded with a physiological Ca2+ ion concentration (2 mm) permeating the channel, and in the absence of channel agonists. Upon depolarization the ensemble-averaged LCC current decayed with a fast and a slow exponential component. We analysed the unitary behaviour responsible for this biphasic decay by means of a novel kinetic dissection of LCC gating parameters. We found that inactivation was caused by a rapid decrease in the frequency of LCC reopening, and a slower decline in mean open time of the LCC. In contrast, with barium ions permeating the channel ensemble-averaged currents displayed only a single, slow exponential decay and little time dependence of the LCC open time. Our results demonstrate that the fast and slow phases of macroscopic inactivation reflect the distinct time courses for the decline in the frequency of LCC reopening and the open dwell time, both of which are modulated by Ca2+ influx. Analysis of the evolution of CDI in individual LCC episodes was employed to examine the stochastic nature of the underlying molecular switch, and revealed that influx on the order of a thousand Ca2+ ions may be sufficient to trigger CDI. This is the first study to characterize both the unitary kinetics and the stoichiometry of CDI of LCCs with a physiological Ca2+ concentration. These novel findings may provide a basis for understanding the mechanisms regulating unitary LCC gating, which is a pivotal element in the local control of Ca2+ -dependent signalling processes. [source] High-resolution structure of human phosphoserine phosphatase in open conformationACTA CRYSTALLOGRAPHICA SECTION D, Issue 6 2003Yves Peeraer The crystal structure of human phosphoserine phosphatase (HPSP) in the open conformation has been determined at a resolution of 1.53,Ĺ. The crystals are orthorhombic, belonging to space group C2221, with unit-cell parameters a = 49.03, b = 130.25, c = 157.29,Ĺ. The asymmetric unit contains two molecules. Phase information was derived from a multiwavelength anomalous dispersion (MAD) experiment conducted at three wavelengths using a selenomethionine-derivative crystal of HPSP. The structure was refined using CNS to a final crystallographic R value of 21.6% (Rfree = 23.4%). HPSP is a dimeric enzyme responsible for the third and final step of the l -serine biosynthesis pathway. It catalyses the Mg2+ -dependent hydrolysis of l -phosphoserine. Recently, the structure of HPSP in complex with an inhibitor bound to the active site has been reported to be the open conformation of the enzyme. Here, the structure of HPSP is reported in the absence of substrate in the active site. Evidence is presented that HPSP in an uncomplexed form is in an even more open conformation than in the inhibitor complex. In this state, the enzyme is partially unfolded to allow the substrate to enter the active site. Binding of the substrate causes HPSP to shift to the closed conformation by stabilizing the partially unfolded region. In the present structure a Ca2+ ion is bound to the active site and an explanation is given why HPSP is not active when in the active site Mg2+ is replaced by a Ca2+ ion. [source] Metal-free MIRAS phasing: structure of apo-S100A3ACTA CRYSTALLOGRAPHICA SECTION D, Issue 8 2002Peer R. E. Mittl S100 proteins are involved in metal-dependent intracellular signalling. Metal-free S100A3, a cysteine-rich Ca2+ - and Zn2+ -binding protein, has been crystallized by vapour diffusion under the strict exclusion of oxygen and in the absence of divalent metal ions. Metal binding induces large conformational changes, rendering the apo-S100A3 crystals very sensitive to various metal compounds. Therefore, the structure was solved by MIRAS phasing using potassium iodide and xenon derivatives. Iodide replaces a water molecule at the surface of the S100A3 protein, whereas xenon binds in a hydrophobic cavity at the dimer interface. Despite significant non-isomorphism, the combination of both derivatives was sufficient for structure determination. The overall apo-S100A3 structure resembles the structures of metal-free S100B and S100A6 solution structures. In contrast to the NMR structures, the EF-hand loops are well ordered in the apo-S100A3 crystal structure. In the N-terminal pseudo-EF-hand loop a water molecule occupies the position of the Ca2+ ion. The C-terminal canonical EF-hand loop shows an extended conformation and a different helix arrangement to other S100/metal complex crystal structures. [source] Gating of the expressed T-type Cav3.1 calcium channels is modulated by Ca2+ACTA PHYSIOLOGICA, Issue 4 2006L. Lacinová Abstract Aim:, We have investigated the influence of Ca2+ ions on the basic biophysical properties of T-type calcium channels. Methods:, The Cav3.1 calcium channel was transiently expressed in HEK 293 cells. Current was measured using the whole cell patch clamp technique. Ca2+ or Na+ ions were used as charge carriers. The intracellular Ca2+ was either decreased by the addition of 10 mm ethyleneglycoltetraacetic acid (EGTA) or increased by the addition of 200 ,m Ca2+ into the non-buffered intracellular solution. Various combinations of extra- and intracellular solutions yielded high, intermediate or low intracellular Ca2+ levels. Results:, The amplitude of the calcium current was independent of intracellular Ca2+ concentrations. High levels of intracellular Ca2+ accelerated significantly both the inactivation and the activation time constants of the current. The replacement of extracellular Ca2+ by Na+ as charge carrier did not affect the absolute value of the activation and inactivation time constants, but significantly enhanced the slope factor of the voltage dependence of the inactivation time constant. Slope factors of voltage dependencies of channel activation and inactivation were significantly enhanced. The recovery from inactivation was faster when Ca2+ was a charge carrier. The number of available channels saturated for membrane voltages more negative than ,100 mV for the Ca2+ current, but did not reach steady state even at ,150 mV for the Na+ current. Conclusions:, Ca2+ ions facilitate transitions of Cav3.1 channel from open into closed and inactivated states as well as backwards transition from inactivated into closed state, possibly by interacting with its voltage sensor. [source] Developmental characteristics of AMPA receptors in chick lumbar motoneuronsDEVELOPMENTAL NEUROBIOLOGY, Issue 11 2007Xianglian Ni Abstract Ca2+ fluxes through ionotropic glutamate receptors regulate a variety of developmental processes, including neurite outgrowth and naturally occurring cell death. In the CNS, NMDA receptors were originally thought to be the sole source of Ca2+ influx through glutamate receptors; however, AMPA receptors also allow a significant influx of Ca2+ ions. The Ca2+ permeability of AMPA receptors is regulated by the insertion of one or more edited GluR2 subunits. In this study, we tested the possibility that changes in GluR2 expression regulate the Ca2+ permeability of AMPA receptors during a critical period of neuronal development in chick lumbar motoneurons. GluR2 expression is absent between embryonic day (E) 5 and E7, but increases significantly by E8 in the chick ventral spinal cord. Increased GluR2 protein expression is correlated with parallel changes in GluR2 mRNA in the motoneuron pool. Electrophysiological recordings of kainate-evoked currents indicate a significant reduction in the Ca2+ -permeability of AMPA receptors between E6 and E11. Kainate-evoked currents were sensitive to the AMPA receptor blocker GYKI 52466. Application of AMPA or kainate generates a significant increase in the intracellular Ca2+ concentration in E6 spinal motoneurons, but generates a small response in older neurons. Changes in the Ca2+ -permeability of AMPA receptors are not mediated by age-dependent changes in the editing pattern of GluR2 subunits. These findings raise the possibility that Ca2+ influx through Ca2+ -permeable AMPA receptors plays an important role during early embryonic development in chick spinal motoneurons. © 2007 Wiley Periodicals, Inc. Develop Neurobiol, 2007 [source] Biphasic Resorbable Calcium Phosphate Ceramic for Bone Implants and Local Alendronate Delivery,ADVANCED ENGINEERING MATERIALS, Issue 5 2010Shashwat S. Banerjee A novel biphasic calcium phosphate ceramic composed of tricalcium phosphate (TCP) and calcium pyrophosphate (CP) is synthesized in order to tailor the biodegradation behavior of the ceramic. The results show that biphasic TCP/CP ceramic has a strength of 62.2,±,2.1 MPa, which is superior to single-phase TCP and CP ceramics, which show strengths of 44.3,±,3.0 and 53.0,±,4.8 MPa, respectively. In addition, biphasic TCP/CP ceramic displays a controlled strength degradation from 62.2,±,2.1 to 40.5,±,1.0 MPa in stimulated body fluid over a period of 28 d. An in vitro cell materials interaction study using human fetal osteoblast cells indicates that TCP/CP ceramic is cytocompatible. TCP/CP ceramic also show a good loading capacity for alendronate. Adsorption of alendronate (AD) on the TCP/CP surface is found to proceed via ligand exchange mechanism and the in vitro release profile of AD from TCP/CP surface is characterized by an initial fast release followed by a slow and sustained release. Strong electrostatic interactions between AD groups and surface Ca2+ ions enable the slow and sustained release of AD. These results demonstrate that the newly developed biphasic ceramic, with its controlled strength degradation and drug release, shows promise for use in orthopedic and tissue engineering applications. [source] Kinetics of Calcium Carbonate (CaCO3) Precipitation from a Icel-Yavca Dolomite Leach Solution by a Gas (Carbon Dioxide)/Liquid ReactionHELVETICA CHIMICA ACTA, Issue 3 2009Mehmet Yildirim Abstract The effects of time, CO2 -gas-injection pressure, and bulk temperature on the precipitation of Ca2+ ions as a precipitated calcium carbonate (PCC) from a dolomite leach solution were investigated. Precipitation periods from 1 to 7,min were examined, and experiments were run at CO2 -injection pressures of 200,800,kPa. Effects of bulk temperature were studied in the range from 40 to 70°, and precipitation rates of PCC were determined by measuring the Ca2+ concentrations in the initial and effluent solutions. Influences of these parameters on the subsequent incorporation of Mg2+ ions with the precipitate are discussed in detail. Kinetic analysis of the precipitation was performed by considering the rates as a function of CO -ion concentrations. Results obtained by this process clearly show that Ca2+ ions in the solution can successfully be precipitated as a calcium carbonate product containing 54.70% of CaO and 0.77% MgO, at the rate of 2.01,mM h,1. [source] Cloning and expression of Bacillus phytase gene (phy) in Escherichia coli and recovery of active enzyme from the inclusion bodiesJOURNAL OF APPLIED MICROBIOLOGY, Issue 4 2008D.E.C.S. Rao Abstract Aims:, To isolate, clone and express a novel phytase gene (phy) from Bacillus sp. in Escherichia coli; to recover the active enzyme from inclusion bodies; and to characterize the recombinant phytase. Methods and Results:, The molecular weight of phytase was estimated as 40 kDa on SDS-polyacrylamide gel electrophoresis. A requirement of Ca2+ ions was found essential both for refolding and activity of the enzyme. Bacillus phytase exhibited a specific activity of 16 U mg,1 protein; it also revealed broad pH and temperature ranges of 5·0 to 8·0 and 25 to 70°C, respectively. The Km value of phytase for hydrolysis of sodium phytate has been determined as 0·392 mmol l,1. The activity of enzyme has been inhibited by EDTA. The enzyme exhibited ample thermostability upon exposure to high temperatures from 75 to 95°C. After 9 h of cultivation of transformed E. coli in the bioreactor, the cell biomass reached 26·81 g wet weight (ww) per l accounting for 4289 U enzyme activity compared with 1·978 g ww per l producing 256 U activity in shake-flask cultures. In silico analysis revealed a ,-propeller structure of phytase. Conclusions:, This is the first report of its kind on the purification and successful in vitro refolding of Bacillus phytase from the inclusion bodies formed in the transformed E. coli. Significance and Impact of the Study:, Efficient and reproducible protocols for cloning, expression, purification and in vitro refolding of Bacillus phytase enzyme from the transformed E. coli have been developed. The novel phytase, with broad pH and temperature range, renaturation ability and substrate specificity, appears promising as an ideal feed supplement. Identification of site between 179th amino acid leucine and 180th amino acid asparagine offers scope for insertion of small peptides/domains for production of chimeric genes without altering enzyme activity. [source] Purification and characterization of an organic solvent and detergent-tolerant novel protease produced by Bacillus sp.JOURNAL OF CHEMICAL TECHNOLOGY & BIOTECHNOLOGY, Issue 11 2008Abstract BACKGROUND: Purification and characterization of a novel protease produced by Bacillus sp. RKY3, has been investigated, with special emphasis on the stability of the enzyme in the presence of different oxidizing and reducing agents as well as organic solvents. The enzyme was purified in two steps through concentration of the crude enzyme by ammonium sulfate precipitation, followed by anion exchange chromatography. RESULTS: The purified protease had a molecular mass of approximately 38 kDa, which was highly active over a broad range of pH between 7.0 and 9.0 and was also stable over a wide pH range from 5.0 to 11.0. Although the optimum temperature for enzyme activity was found to be 60 °C, it was rapidly deactivated at temperatures above 60 °C. It also showed good stability at 50 °C, with a 70 min half-life. Ca2+ ions did not greatly enhance the activity or the stability of the enzyme. PMSF (1 mmol L,1) completely inhibited the protease activity, and thus the purified protease was considered to be serine protease. The purified protease was stable with oxidants (H2O2, 2%), reducing agents (sodium dodecyl sulfate, 2%), and organic solvents (25%) such as benzene, hexane, and toluene. CONCLUSION: The purified enzyme, protease, seems to possess potential applications in protease-based detergent and bleaching industries. The enzymatic activity against a wide variety of substrates suggests that the purified enzyme should be investigated for a range of commercial applications, especially for soy protein and gelatin hydrolysis in the food processing industry. Copyright © 2008 Society of Chemical Industry [source] CREB-dependent Nur77 induction following depolarization in PC12 cells and neurons is modulated by MEF2 transcription factorsJOURNAL OF NEUROCHEMISTRY, Issue 4 2010Brian Yee Hong Lam J. Neurochem. (2010) 112, 1065,1073. Abstract Expression of the nuclear orphan receptor gene Nur77 in neuronal cells is induced by activity-dependent increases in intracellular Ca2+ ions. Ca2+ responsiveness of the Nur77 gene has been attributed to two distinct DNA regulatory regions that recruit the transcription factors cAMP response element binding protein (CREB) and myocyte enhancer factor-2 (MEF2). Here we used dominant interfering and constitutively active mutants of CREB and MEF2 proteins to assess their relative contribution to depolarization-induced Nur77 expression in undifferentiated PC12 cells and hippocampal neurons. We show that while CREB is necessary for Ca2+ -activated Nur77 expression MEF2 functions to modulate CREB-dependent Nur77 expression by acting as a repressor in quiescent cells. [source] Ca2+ -Mediated Interaction Between Microsilica and Polycarboxylate Comb Polymers in a Model Cement Pore SolutionJOURNAL OF THE AMERICAN CERAMIC SOCIETY, Issue 10 2010Matthias Lesti Interaction between polycarboxylate (PCE) comb polymers and microsilica suspended in a highly alkaline, Ca2+ -loaded model cement pore solution was studied via zeta potential, adsorption, and paste flow experiments. Zeta potential measurements reveal that in an alkaline suspension, microsilica possesses a negative surface charge stemming from deprotonated silanolate groups. Addition of soluble calcium salts (e.g., CaCl2) was found to cause a charge reversal to positive, owing to the adsorption of Ca2+ ions forming a monolayer on the microsilica surface. Further experiments demonstrate that through Ca2+ mediation, anionic PCE graft polymers adsorb in high amount on the microsilica surface. Polymers possessing a stronger anionic character exhibit a higher affinity to the positive microsilica surface, and consequently, exercise a more powerful dispersing effect than PCE showing less anionic character. A model summarizing the processes occurring at the surface of microsilica in this fluid system is proposed. The study suggests that the high fluidity of concrete containing microsilica depends on the effective dispersion of microsilica, and not of cement. [source] Calcium Phosphate Crystallization on Electrospun Cellulose Non-Woven Fabrics Containing Synthetic Phosphorylated PolypeptidesMACROMOLECULAR MATERIALS & ENGINEERING, Issue 5 2009Shinya Hayashi Abstract The preparation of electrospun non-woven fabrics composed of cellulose and synthetic phosphorylated polypeptides, copoly[Ser(PO3H2)XAspY]s (X:Y,=,100:0, 75:25, 50:50, 25:75), is described. The non-wovens were subjected to an alternate immersion in CaCl2 and Na2HPO4 solutions to induce crystallization of calcium phosphate. The deposited calcium phosphate crystals were analyzed by means of EDX analysis and WXRD. The amounts of calcium phosphate deposition are greater for the cellulose non-woven fabrics containing copoly[Ser(PO3H2)XAspY] than those of cellulose-only non-woven fabrics. These results indicate that copoly[Ser(PO3H2)XAspY] can entrap Ca2+ ions around the fine fiber matrix to accelerate crystallization of the calcium phosphate. [source] Tartaric Acid Starch Ether: A Novel Biopolymer-Based PolyelectrolyteMACROMOLECULAR RAPID COMMUNICATIONS, Issue 16 2003Carsten Grote Abstract New tartaric acid starch ethers have been synthesized applying starch sources of different amylose content. The reactions were carried out heterogeneously in ethanol/water mixtures with cis -disodiumepoxysuccinate as etherifying reagent leading to products of a degree of substitution (DS) up to 0.3. The molecular structure of the new starch ethers was evaluated by elemental analysis, FTIR and 13C NMR spectroscopy. Preliminary studies using a convenient titration method indicate a high binding capacity for Ca2+ ions which is dependent on the starch source and DS. Tartaric acid starch ethers. [source] Synergistic or additive corrosion inhibition of mild steel by a mixture of HEDP and metasilicate at pH 7 and 11MATERIALS AND CORROSION/WERKSTOFFE UND KORROSION, Issue 11 2004D. Mohammedi Abstract Electrochemical measurements (steady-state current-voltage curves and AC impedance) were coupled with mass-loss measurements, SEM examinations, and EDSX analyses to investigate the inhibition of corrosion of a carbon steel by a mixture of phosphonic acid HEDP (acid 1, hydroxyethylene, 1-1 diphosphonic) and sodium metasilicate pentahydrate Na2SiO3. 5H2O in an industrial hard water containing 3.10,3 M Ca2+ ions. At pH 7, HEDP and Ca2+ act in a synergistic manner, by formation of a HEDP and calcium containing layer. Addition of silicate at this pH value, allows to reach an efficiency of 94% due to an additive inhibition effect. At pH 11, metasilicate, HEDP, and Ca2+ ions reinforce the passive layer in a synergistic way. The mixture (1.7 · 10,5 M HEDP + 2.6 · 10 -3 M SiO2,3) in the Ca2+ containing electrolyte is shown to be able to inhibit efficaciously the corrosion of iron at room temperature, considering uniform corrosion at pH 7 or pitting corrosion at pH 11. [source] Deterioration in mechanical properties of glass fiber-reinforced nylon 6,6 composites by aqueous calcium chloride mixture solutionsPOLYMER COMPOSITES, Issue 4 2009D. Manjula Dhevi In this article, nylon 6,6 (NY66) and glass fiber-(30 wt%) reinforced NY66 (GFNY66) specimens were immersed in various aqueous calcium chloride (aq. CaCl2) mixture solutions at different thermal conditions for varying intervals of time, and analyzed using attenuated total reflection-infrared (ATR-IR) spectroscopy, inductively coupled plasma (ICP), energy dispersive X-ray (EDX), gel permeation chromatography (GPC), and mechanical studies. ICP data revealed increasing concentration of absorbed Ca2+ ions with increasing immersion time resulting in disruption of intra- and intermolecular H-bonding as confirmed using ATR-IR results. From EDX data, the ratio of Ca2+ and Cl, ions absorbed by NY66 was calculated and found to follow its stoichiometric equivalence. GPC data exhibited less reduction in Mn and Mw for aq. CaCl2 -treated NY66 specimens suggesting the absence of any significant chemical degradation, but the occurrence of only physical changes involving H-bond breakage and the formation of new CO···Ca2+ dative bond in NY66 matrix. The mechanical properties of GFNY66 samples treated with various types of aq. CaCl2 solutions exhibited pronounced deterioration, possibly due to the interfacial failure between glass fiber and NY66 matrix. The results obtained from this study were quite useful toward understanding the degradation mechanism in NY66 and GFNY66 caused by various aq. CaCl2 mixture solutions, and will be helpful in improving the mechanical properties of recycled NY66. POLYM. COMPOS., 2009. © 2008 Society of Plastics Engineers [source] Ca2+ -dependent components of inactivation of unitary cardiac L-type Ca2+ channelsTHE JOURNAL OF PHYSIOLOGY, Issue 1 2010Ira R. Josephson A Ca2+ ion-dependent inactivation (CDI) of L-type Ca2+ channels (LCC) is vital in limiting and shaping local Ca2+ ion signalling in a variety of excitable cell types. However, under physiological conditions the unitary LCC properties that underlie macroscopic inactivation are unclear. Towards this end, we have probed the gating kinetics of individual cardiac LCCs recorded with a physiological Ca2+ ion concentration (2 mm) permeating the channel, and in the absence of channel agonists. Upon depolarization the ensemble-averaged LCC current decayed with a fast and a slow exponential component. We analysed the unitary behaviour responsible for this biphasic decay by means of a novel kinetic dissection of LCC gating parameters. We found that inactivation was caused by a rapid decrease in the frequency of LCC reopening, and a slower decline in mean open time of the LCC. In contrast, with barium ions permeating the channel ensemble-averaged currents displayed only a single, slow exponential decay and little time dependence of the LCC open time. Our results demonstrate that the fast and slow phases of macroscopic inactivation reflect the distinct time courses for the decline in the frequency of LCC reopening and the open dwell time, both of which are modulated by Ca2+ influx. Analysis of the evolution of CDI in individual LCC episodes was employed to examine the stochastic nature of the underlying molecular switch, and revealed that influx on the order of a thousand Ca2+ ions may be sufficient to trigger CDI. This is the first study to characterize both the unitary kinetics and the stoichiometry of CDI of LCCs with a physiological Ca2+ concentration. These novel findings may provide a basis for understanding the mechanisms regulating unitary LCC gating, which is a pivotal element in the local control of Ca2+ -dependent signalling processes. [source] Ca4IrO6, Ca3MgIrO6 and Ca3ZnIrO6ACTA CRYSTALLOGRAPHICA SECTION C, Issue 11 2001Matthew J. Davis Single crystals of tetracalcium iridium hexaoxide, Ca4IrO6, tricalcium magnesium iridium hexaoxide, Ca3MgIrO6, and tricalcium zinc iridium hexaoxide, Ca3ZnIrO6, were prepared via high-temperature flux growth and structurally characterized by single-crystal X-ray diffraction. The three compounds are isostructural and adopt the K4CdCl6 structure type, comprised of chains of alternating face-shared [CaO6], [MgO6] or [ZnO6] trigonal prisms and [IrO6] octahedra, surrounded by columns of Ca2+ ions. [source] Observation of a calcium-binding site in the ,-class carbonic anhydrase from Pyrococcus horikoshiiACTA CRYSTALLOGRAPHICA SECTION D, Issue 10 2008Jeyaraman Jeyakanthan Carbonic anhydrases are zinc-containing metalloenzymes that catalyze the interconversion of carbon dioxide and bicarbonate. Three crystal structures of ,-class carbonic anhydrase (one of which is bound to a bicarbonate molecule) from the aerobic OT3 strain of the hyperthermophilic archeon Pyrococcus horikoshii have been solved by molecular replacement in space group F4132. The asymmetric unit contains a monomer of 173 amino acids and a catalytic Zn2+ ion. The protein fold is a regular prism formed by a left-handed ,-helix, similar to previously reported structures. The active-site Zn2+ ion located at the interface between the two monomers is bound to three histidyl residues and a water molecule in a tetrahedral fashion. In addition to the 20 ,-strands comprising the ,-helix, there is also a long C-terminal ,-helix. For the first time, Ca2+ ions have been observed in addition to the catalytic Zn2+ ion. It is hypothesized that Tyr159 (which corresponds to the catalytically important Asn202 in previously reported structures) utilizes C,H..., interactions to fulfill its functions. This study may shed light on the catalytic mechanism of the enzyme and throw open new questions on the mechanism of product removal in carbonic anhydrases. [source] The endoproteinase furin contains two essential Ca2+ ions stabilizing its N-terminus and the unique S1 specificity pocketACTA CRYSTALLOGRAPHICA SECTION D, Issue 5 2005Manuel E. Than The mammalian prohormone/proprotein convertase (PC) furin is responsible for the maturation of a great variety of homeostatic but also many pathogenic proteins within the secretory pathway and the endosomal pathway and at the cell surface. Similar to other members of the PC family, furin requires calcium for catalytic activity. In a previous paper, the structural association of the catalytic and the P-domain of furin was shown and data were presented indicating two or three calcium-binding sites. The exact number and the three-dimensional localization of the essential calcium sites within furin have now been determined by collecting X-ray diffraction data on either side of the Ca,K absorption edge and by calculating a novel type of double difference map from these anomalous scattering data. Two calcium ions were unambiguously identified: the purely structural Ca-1 also conserved in the bacterial digestive subtilisins and the Ca-2 site specific to PCs and essential for the formation of the P1 specificity-determining S1-binding pocket. In addition, these anomalous diffraction data show that no tightly bound K+ sites exist in furin. [source] Calcium-Induced Membrane Microdomains Trigger Plant Phospholipase D ActivityCHEMBIOCHEM, Issue 17 2008Konstantin Kuppe Abstract Plant ,-type phospholipase D proteins are calcium-dependent, lipolytic enzymes. The morphology of the aggregates of their phospholipid substrate fundamentally defines the interaction between the enzyme and the surface. Here we demonstrate that the Ca2+ -induced generation of membrane microdomains dramatically activates ,-type phospholipase D from white cabbage. 500-fold stimulation was observed upon incorporation of 10 mol,% 1-palmitoyl-2-oleoyl- sn -glycero-3-phosphate (POPA) into 1-palmitoyl-2-oleoyl- sn -glycero-3-phosphocholine (POPC) vesicles in the presence of Ca2+ ions. Enhanced association of PLD,2 with phospholipid surfaces containing anionic components was indicated by lag phase analysis and film balance measurements. Differential scanning calorimetry showed that the POPA-specific activation correlates with the phase behavior of the POPC/POPA vesicles in the presence of Ca2+ ions. We conclude from the results that the Ca2+ -induced formation of POPA microdomains is the crucial parameter that facilitates the binding of PLD to the phospholipid surface and suggest that this effect serves as a cellular switch for controlling PLD activity. [source] Production and Characteristics of an Enantioselective Lipase from Burkholderia sp.CHEMICAL ENGINEERING & TECHNOLOGY (CET), Issue 2 2008GXU5 Abstract The lipase production of Burkholderia sp. GXU56 was influenced by carbon and nitrogen sources, inorganic salts, initial pH of the medium and cultivation temperature. The maximum lipase production was 580.52,U/mL and reached 5,times the level of the basic medium in the optimum medium at pH 8.0, 32,°C, 200,rpm and 40,48,h. The lipase was purified 53.6,fold to homogeneity and the molecular weight was 35,KDa on SDS-PAGE. The optimum pH and temperature of the lipase were 8.0 and 40,°C, respectively, and it was stable in the range of pH 7,8.5 and at temperatures below 45,°C. The lipase activity was strongly inhibited by Zn2+, Cu2+, Co2+, Fe2+, Fe3+ ions and SDS, while it was stimulated by Li+ and Ca2+ ions and in presence of 0.1,% CTAB, 0.1,% Triton X-100 and 10,% DMSO. Km and Vmax of the lipase were calculated to be 0.038,mmol/L, and 0.029,mmol/L min,1, respectively, with PNPB as the substrate. The GXU56 lipase showed enantioselective hydrolysis of (R,S)-methyl mandelate to (R)-mandelic acid, which is an important intermediate in the pharmaceutical industry. [source] Convenient Synthesis of Multifunctional EDTA-Based Chiral Metal Chelates Substituted with an S -MesylcysteineCHEMISTRY - A EUROPEAN JOURNAL, Issue 11 2005Andrei Leonov Dr. Abstract We describe the synthetic route to ethylenediaminetetraacetic acid (EDTA) derivatives that can be attached to surface-exposed thiol functional groups of cysteine residues in proteins, via a methylthiosulfonate moiety that is connected in a stereochemically unique way to the C-1 carbon atom of EDTA. Such compounds can be used to align proteins in solution without the need to add liquid crystalline media, and are, therefore, of great interest for the NMR spectroscopic analysis of biomolecules. The binding constant for the paramagnetic tag to lanthanide ions was determined by measuring luminescence. For the Tb+3,ligand complex, a Kb value of 6.5×1017,M,1 was obtained. This value is in excellent agreement with literature values for the related EDTA compound. In addition, it could be shown that there is no significant reduction in the luminescence intensity upon addition of a 104 excess of Ca2+ ions, indicating that this paramagnetic tag is compatible with buffers containing high concentrations of divalent alkaline earth ions. [source] | ||||||||||||||||||||||||||||