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Phosphate Ions (phosphate + ion)
Selected AbstractsA Metal,Macrocycle Complex as a Fluorescent Sensor for Biological Phosphate Ions in Aqueous SolutionEUROPEAN JOURNAL OF ORGANIC CHEMISTRY, Issue 10 2010Xiao-huan Huang Abstract We synthesized tetraazamacrocycles 1 and 2 bearing two anthryl groups as sidearms, both of which exhibited high selectivity for the ZnII ion in switching-on-type responses in aqueous solution. For ligand 1, ZnII is coordinated by four nitrogen atoms of the macrocycle and two amino groups on the pendent arms, which results in proximity between the twofluorophores. So, 1 -ZnII shows obvious excimer emission in aqueous solution. When PPi or ATP was added (pH 7.4), the excimer emission of 1 -ZnII was quenched, whereas monomer emission was revived. To the best of our knowledge, no other known sensor has this characteristic under physiological pH conditions. At the same time, the obvious different fluorescence response of 1 -ZnII for PPi and ATP in water shows that receptor 1 -ZnII can be used as a selective fluorescent chemosensor for PPi and ATP anions. [source] Structure of grouper iridovirus purine nucleoside phosphorylaseACTA CRYSTALLOGRAPHICA SECTION D, Issue 2 2010You-Na Kang Purine nucleoside phosphorylase (PNP) catalyzes the reversible phosphorolysis of purine ribonucleosides to the corresponding free bases and ribose 1-phosphate. The crystal structure of grouper iridovirus PNP (givPNP), corresponding to the first PNP gene to be found in a virus, was determined at 2.4,Ĺ resolution. The crystals belonged to space group R3, with unit-cell parameters a = 193.0, c = 105.6,Ĺ, and contained four protomers per asymmetric unit. The overall structure of givPNP shows high similarity to mammalian PNPs, having an ,/, structure with a nine-stranded mixed ,-barrel flanked by a total of nine ,-helices. The predicted phosphate-binding and ribose-binding sites are occupied by a phosphate ion and a Tris molecule, respectively. The geometrical arrangement and hydrogen-bonding patterns of the phosphate-binding site are similar to those found in the human and bovine PNP structures. The enzymatic activity assay of givPNP on various substrates revealed that givPNP can only accept 6-oxopurine nucleosides as substrates, which is also suggested by its amino-acid composition and active-site architecture. All these results suggest that givPNP is a homologue of mammalian PNPs in terms of amino-acid sequence, molecular mass, substrate specificity and overall structure, as well as in the composition of the active site. [source] Structural analysis of Tityus serrulatus Ts1 neurotoxin at atomic resolution: insights into interactions with Na+ channelsACTA CRYSTALLOGRAPHICA SECTION D, Issue 3 2003Carlos Basílio Pinheiro The structure of the Ts1 toxin from the Brazilian scorpion Tityus serrulatus was investigated at atomic resolution using X-ray crystallography. Several positively charged niches exist on the Ts1 molecular surface, two of which were found to coordinate phosphate ions present in the crystallization solution. One phosphate ion is bound to the conserved basic Lys1 residue at the Ts1 N-terminus and to residue Asn49. The second ion was found to be caged by residues Lys12, Trp54 and Arg56. Lys12 and Tyr/Trp54 residues are strictly conserved in all classical scorpion ,-neurotoxins. The cavity formed by these residues may represent a special scaffold required for interaction between ,-neurotoxins and sodium channels. The charge distribution on the Ts1 surface and the results of earlier chemical modification studies and side-directed mutagenesis experiments strongly indicate that the phosphate-ion positions mark plausible binding sites to the Na+ channel. The existence of two distinct binding sites on the Ts1 molecular surface provides an explanation for the competition between Ts1, depressant (LqhIT2) and excitatory (AaHIT) neurotoxins. [source] Preliminary X-ray crystallographic analysis of the d -xylulose 5-phosphate phosphoketolase from Lactococcus lactisACTA CRYSTALLOGRAPHICA SECTION F (ELECTRONIC), Issue 7 2010Georgiana Petrareanu Phosphoketolases are thiamine diphosphate-dependent enzymes which play a central role in the pentose-phosphate pathway of heterofermentative lactic acid bacteria. They belong to the family of aldehyde-lyases and in the presence of phosphate ion cleave the carbon,carbon bond of the specific substrate d -xylulose 5-phosphate (or d -fructose 6-phosphate) to give acetyl phosphate and d -glyceraldehyde 3-phosphate (or d -erythrose 4-phosphate). Structural information about phosphoketolases is particularly important in order to fully understand their mechanism as well as the steric course of phosphoketolase-catalyzed reactions. Here, the purification, preliminary crystallization and crystallographic characterization of d -xylulose 5-phosphate phosphoketolase from Lactococcus lactis are reported. The presence of thiamine diphosphate during purification was essential for the enzymatic activity of the purified protein. The crystals belonged to the monoclinic space group P21. Diffraction data were obtained to a resolution of 2.2,Ĺ. [source] New structural insights and molecular-modelling studies of 4-methyl-5-,-hydroxyethylthiazole kinase from Pyrococcus horikoshii OT3 (PhThiK)ACTA CRYSTALLOGRAPHICA SECTION F (ELECTRONIC), Issue 10 2009Jeyaraman Jeyakanthan 4-Methyl-5-,-hydroxyethylthiazole kinase (ThiK) catalyses the phosphorylation of the hydroxyl group of 4-methyl-5-,-hydroxyethylthiazole. This work reports the first crystal structure of an archaeal ThiK: that from Pyrococcus horikoshii OT3 (PhThiK) at 1.85,Ĺ resolution with a phosphate ion occupying the position of the ,-phosphate of the nucleotide. The topology of this enzyme shows the typical ribokinase fold of an ,/, protein. The overall structure of PhThiK is similar to those of Bacillus subtilis ThiK (BsThiK) and Enterococcus faecalis V583 ThiK (EfThiK). Sequence analysis of ThiK enzymes from various sources indicated that three-quarters of the residues involved in interfacial regions are conserved. It also revealed that the amino-acid residues in the nucleotide-binding, magnesium ion-binding and substrate-binding sites are conserved. Binding of the nucleotide and substrate to the ThiK enzyme do not influence the quaternary association (trimer) as revealed by the crystal structure of PhThiK. [source] Proposal for molecular mechanism of thionins deduced from physico-chemical studies of plant toxinsCHEMICAL BIOLOGY & DRUG DESIGN, Issue 6 2004B. Stec Abstract:, We propose a molecular model for phospholipid membrane lysis by the ubiquitous plant toxins called thionins. Membrane lysis constitutes the first major effect exerted by these toxins that initiates a cascade of cytoplasmic events leading to cell death. X-ray crystallography, solution nuclear magnetic resonance (NMR) studies, small angle X-ray scattering and fluorescence spectroscopy provide evidence for the mechanism of membrane lysis. In the crystal structures of two thionins in the family, ,1 - and , -purothionins (MW: approximately 4.8 kDa), a phosphate ion and a glycerol molecule are modeled bound to the protein. 31P NMR experiments on the desalted toxins confirm phosphate-ion binding in solution. Evidence also comes from phospholipid partition experiments with radiolabeled toxins and with fluorescent phospholipids. This data permit a model of the phospholipid,protein complex to be built. Further, NMR experiments, one-dimensional (1D)- and two-dimensional (2D)-total correlation spectroscopy (TOCSY), carried out on the model compounds glycerol-3-phosphate (G3P) and short chain phospholipids, supported the predicted mode of phospholipid binding. The toxins' high positive charge, which renders them extremely soluble (>300 mg/mL), and the phospholipid-binding specificity suggest the toxin,membrane interaction is mediated by binding to patches of negatively charged phospholipids [phosphatidic acid (PA) or phosphatidyl serine (PS)] and their subsequent withdrawal. The formation of proteolipid complexes causes solubilization of the membrane and its lysis. The model suggests that the oligomerization may play a role in toxin's activation process and provides insight into the structural principles of protein,membrane interactions. [source] Caries clinical trial of a remineralising toothpaste in radiation patientsGERODONTOLOGY, Issue 2 2008Athena Papas Objectives:, The purpose of this study was to determine the efficacy and safety of a specially formulated remineralising toothpaste in controlling caries in a high-risk population: head and neck radiation patients. Design:, The study compared the performance of the remineralising toothpaste with a conventional fluoride dentifrice using double-blind randomisation. Materials and methods:,Test products: The products compared contained equivalent quantities of fluoride (1100 p.p.m.). The dual-phase remineralising toothpaste, Enamelon®, also delivered soluble calcium and phosphate ions, essential components of teeth, from separate phases. Both groups had all caries restored at baseline and used a fluoride rinse daily. Subjects: Fifty-seven subjects who received radiation to the head and neck causing saliva hypofunction, entered the study, while 44 completed the 10,12 month visit. Measurements: Examinations included coronal and root caries using the Pitts Diagnostic Criteria, salivary flow rate, plaque and gingival indices and microbiological counts over a 1-year period. Results:, The average net increment per year for root caries per subject was 0.04 (±.052) in subjects completing the study using the remineralising toothpaste and 1.65 (±0.51) for root caries in subjects completing the study using the conventional fluoride dentifrice. The difference was statistically significant (p = 0.03), suggesting lower net root surface increment/year for the remineralising toothpaste relative to the conventional toothpaste. No significant differences were noted on coronal surfaces. Conclusion:, The results indicate that the remineralising toothpaste provides a significant benefit in preventing and remineralising root caries in high-risk patients. [source] Isolation and selection of Bacillus spp. as potential biological agents for enhancement of water quality in culture of ornamental fishJOURNAL OF APPLIED MICROBIOLOGY, Issue 5 2007R. Lalloo Abstract Aims:, To isolate, select and evaluate Bacillus spp. as potential biological agents for enhancement of water quality in culture of ornamental fish. Methods and Results:, Natural isolates obtained from mud sediment and Cyprinus carpio were purified and assessed in vitro for efficacy based on the inhibition of growth of pathogenic Aeromonas hydrophila and the decrease in concentrations of ammonium, nitrite, nitrate and phosphate ions. Based on suitability to predefined characteristics, the isolates B001, B002 and B003 were selected and evaluated in vitro in the presence of Aer. hydrophila and in a preliminary in vivo trial with C. carpio. The inhibitory effect on pathogen growth and the decrease in concentrations of waste ions was demonstrated. Based on 16S RNA sequence homology, the isolates were identified as Bacillus subtilis, Bacillus cereus and Bacillus licheniformis, respectively. Isolate B002 did not contain the anthrax virulence plasmids pOX1, pOX2 or the B. cereus enterotoxin. Conclusions:, Selected isolates effected synergistic reduction in pathogen load and the concentrations of waste ions in vitro and in vivo and are safe for use in ornamental aquaculture. Significance and Impact of the Study:, A new approach for assessment of biological agents was demonstrated and has yielded putative isolates for development into aquaculture products. [source] Effect of particle size of an amorphous calcium phosphate filler on the mechanical strength and ion release of polymeric composites,JOURNAL OF BIOMEDICAL MATERIALS RESEARCH, Issue 1 2007Soo-Young Lee Abstract The random clustering of amorphous calcium phosphate (ACP) particles within resin matrices is thought to diminish the strength of their polymerized composites. The objective of this study was to elucidate the effect of ball-milling on the particle size distribution (PSD) of ACP fillers and assess if improved dispersion of milled ACP in methacrylate resin sufficiently enhanced filler/matrix interactions to result in improved biaxial flexure strength (BFS), without compromising the remineralizing potential of the composites. Unmilled and wet-milled zirconia-hybridized ACP (Zr-ACP) fillers were characterized by PSD analysis, X-ray diffraction, thermogravimetric and chemical analysis, infrared spectroscopy, and scanning electron microscopy. Composite specimens made from a photoactivated, ternary methacrylate resin admixed with a mass fraction of 40% of un-milled or milled Zr-ACP were evaluated for the BFS (dry and wet) and for the release of calcium and phosphate ions into saline solutions. While having no apparent effect on the structure, composition, and morphology/topology of the fillers, milling significantly reduced the average size of Zr-ACP particulates (median diameter, dm = 0.9 ± 0.2 ,m) and the spread of their PSD. Better dispersion of milled Zr-ACP in the resins resulted in the improved BFS of the composites, even after aqueous soaking, and also gave a satisfactory ion release profile. The demonstrated improvement in the mechanical stability of anti-demineralizing/remineralizing ACP composites based on milled Zr-ACP filler may be beneficial in potentially extending their dental utility. © 2006 Wiley Periodicals, Inc. J Biomed Mater Res Part B: Appl Biomater, 2007 [source] Highly Ordered Interstitial Water Observed in Bone by Nuclear Magnetic Resonance,JOURNAL OF BONE AND MINERAL RESEARCH, Issue 4 2005Erin E Wilson Abstract NMR was used to study the nanostructure of bone tissue. Distance measurements show that the first water layer at the surface of the mineral in cortical bone is structured. This water may serve to couple the mineral to the organic matrix and may play a role in deformation. Introduction: The unique mechanical characteristics of bone tissue have not yet been satisfactorily connected to the exact molecular architecture of this complex composite material. Recently developed solid-state nuclear magnetic resonance (NMR) techniques are applied here to the mineral component to provide new structural distance constraints at the subnanometer scale. Materials and Methods: NMR dipolar couplings between structural protons (OH, and H2O) and phosphorus (PO4) or carbon (CO3) were measured using the 2D Lee-Goldburg Cross-Polarization under Magic-Angle Spinning (2D LG-CPMAS) pulse sequence, which simultaneously suppresses the much stronger proton-proton dipolar interactions. The NMR dipolar couplings measured provide accurate distances between atoms, e.g., OH and PO4 in apatites. Excised and powdered femoral cortical bone was used for these experiments. Synthetic carbonate (,2-4 wt%)-substituted hydroxyapatite was also studied for structural comparison. Results: In synthetic apatite, the hydroxide ions are strongly hydrogen bonded to adjacent carbonate or phosphate ions, with hydrogen bond (O-H) distances of ,1.96 Ĺ observed. The bone tissue sample, in contrast, shows little evidence of ordered hydroxide. Instead, a very ordered (structural) layer of water molecules is identified, which hydrates the small bioapatite crystallites through very close arrangements. Water protons are ,2.3-2.55 Ĺ from surface phosphorus atoms. Conclusions: In synthetic carbonated apatite, strong hydrogen bonds were observed between the hydroxide ions and structural phosphate and carbonate units in the apatite crystal lattice. These hydrogen bonding interactions may contribute to the long-range stability of this mineral structure. The biological apatite in cortical bone tissue shows evidence of hydrogen bonding with an ordered surface water layer at the faces of the mineral particles. This structural water layer has been inferred, but direct spectroscopic evidence of this interstitial water is given here. An ordered structural water layer sandwiched between the mineral and the organic collagen fibers may affect the biomechanical properties of this complex composite material. [source] Chitosan-Pectin Composite Gel Spheres: Effect of Some Formulation Variables on Drug ReleaseMACROMOLECULAR SYMPOSIA, Issue 1 2004Pornsak Sriamornsak Abstract Chitosan-pectin composite gel spheres were prepared by ionotropic gelation method. Pectin solution containing indomethacin, a model drug, was extruded into a mixture of chitosan and calcium chloride. The release behavior of indomethacin from composite gel spheres was investigated in-vitro. The influence of factors affecting release behavior, such as type of pectin, molecular weight of chitosan, cross-linking time and release medium, were discussed in this study. Adding chitosan into gelation medium could retard the release of indomethacin from gel spheres. The different type of pectin used demonstrated slightly different drug release profiles. The higher molecular weight of chitosan showed less indomethacin release than the lower one. The increased cross-linking time slowed the drug release from composite gel spheres. The release of indomethacin from composite gel spheres was also dependent on the release medium. The drug release was slower in tris buffer where no phosphate ions which can induce the precipitation of calcium phosphate. The results suggested that the composite gel spheres of pectin and chitosan could be used as a controlled release drug delivery carrier. [source] A Novel In Vitro Assessment of Tissue Valve Calcification by a Continuous Flow Type MethodARTIFICIAL ORGANS, Issue 2 2000Jong-Chul Park Abstract: A dynamic flow type testing to study calcification was self-designed to investigate calcification in bioprosthetic heart valves. The apparatus consists of a container into which leaflets from a porcine aortic valve are placed, a chamber that contains calcium solution, and a peristaltic pump that provides a continuous supply of the solution toward the container. Efficacy of the apparatus was compared with the conventional batch type calcification testing at 37°C through measuring the amount of calcium and phosphate deposited by inductively coupled plasma (ICP) and scanning electron microscope (SEM). After 14 days, calcium levels detected from the calcified deposit on leaflets were 470.4 ± 37.0 ,g/cm3 in the flow type testing whereas in the batch type testing levels were 81.0 ± 6.7 ,g/cm3. Though the calcium level on the leaflet increased as the exposure time to calcium solution increased in both testings, the rate and the tendency of calcification could be assessed very rapidly by flow type testing in comparison with batch type testing. [Ca]/[P] molar ratio decreased over time, and after 14 days, the ratio was close to 1.83 ± 0.18 in the flow type testing. The ratio could not be determined in the batch type testing because the deposit was too small to assess. The descending rate of [Ca]/[P] molar ratio demonstrates that deposited calcium-complex at the earliest stage may interact with inorganic phosphate ions to create a calcified deposit mineral precursor. This in vitro dynamic flow type calcification testing was a favorable tool for rapid investigation of calcification. [source] Structure of murine angiogenin: features of the substrate- and cell-binding regions and prospects for inhibitor-binding studiesACTA CRYSTALLOGRAPHICA SECTION D, Issue 12 2005Daniel E. Holloway Angiogenin is an unusual member of the pancreatic ribonuclease superfamily that induces blood-vessel formation and is a promising anticancer target. The three-dimensional structure of murine angiogenin (mAng) has been determined by X-ray crystallography. Two structures are presented: one is a complex with sulfate ions (1.5,Ĺ resolution) and the other a complex with phosphate ions (1.6,Ĺ resolution). Residues forming the putative B1, P1 and B2 subsites occupy positions similar to their hAng counterparts and are likely to play similar roles. The anions occupy the P1 subsite, sulfate binding conventionally and phosphate adopting two orientations, one of which is novel. The B1 subsite is obstructed by Glu116 and Phe119, with the latter assuming a less invasive position than its hAng counterpart. Hydrophobic interactions between the C-terminal segment and the main body of the protein are more extensive than in hAng and may underly the lower enzymatic activity of the murine protein. Elsewhere, the structure of the H3,B2 loop supports the view that hAng Asn61 interacts directly with cell-surface molecules and does not merely stabilize adjacent regions of the hAng structure. mAng crystals appear to offer small-molecule inhibitors a clear route to the active site and may even withstand a reorientation of the C-terminal segment that provides access to the cryptic B1 subsite. These features represent considerable advantages over crystalline hAng and bAng. [source] Structural analysis of Tityus serrulatus Ts1 neurotoxin at atomic resolution: insights into interactions with Na+ channelsACTA CRYSTALLOGRAPHICA SECTION D, Issue 3 2003Carlos Basílio Pinheiro The structure of the Ts1 toxin from the Brazilian scorpion Tityus serrulatus was investigated at atomic resolution using X-ray crystallography. Several positively charged niches exist on the Ts1 molecular surface, two of which were found to coordinate phosphate ions present in the crystallization solution. One phosphate ion is bound to the conserved basic Lys1 residue at the Ts1 N-terminus and to residue Asn49. The second ion was found to be caged by residues Lys12, Trp54 and Arg56. Lys12 and Tyr/Trp54 residues are strictly conserved in all classical scorpion ,-neurotoxins. The cavity formed by these residues may represent a special scaffold required for interaction between ,-neurotoxins and sodium channels. The charge distribution on the Ts1 surface and the results of earlier chemical modification studies and side-directed mutagenesis experiments strongly indicate that the phosphate-ion positions mark plausible binding sites to the Na+ channel. The existence of two distinct binding sites on the Ts1 molecular surface provides an explanation for the competition between Ts1, depressant (LqhIT2) and excitatory (AaHIT) neurotoxins. [source] Relationship between quantitative assessments of salivary buffering capacity and ion activity product for hydroxyapatite in relation to cariogenic potentialAUSTRALIAN DENTAL JOURNAL, Issue 2 2008H Aiuchi Abstract Background:, The ion activity product for hydroxyapatite (IpHA) is a comprehensive parameter reflecting pH, calcium and phosphate ion concentration in saliva which govern the degree of saturation with respect to the dissolving tooth mineral. The aim of this study was to evaluate the relationship between quantitative assessments of salivary buffering capacity and IpHA in relation to cariogenic potential. Methods:, Stimulated whole saliva was collected from 33 patients, and the initial pH of samples was measured using a hand-held pH meter. Then samples were titrated with 0.1 N HCl to evaluate buffering capacities and divided into three groups (high, medium and low). After measuring concentrations of calcium and phosphate ions in the samples, IpHA was calculated using the values of the ion concentrations and pH. Differences in the mean pH values, the concentrations of calcium, phosphate ions and log[IpHA] among three groups were analysed using the Kruskal Wallis and the Mann-Whitney non-parametric test, p < 0.05. Results:, After HCl 50 ,L titration, there were statistical differences of the mean pH and IpHA among each buffering capacity group. Moreover, after 50 ,L HCl titration, there was an excellent correlation between the buffer capacity and log[IpHA]. Conclusions:, The pH change for saliva after HCl titration has a significant influence on the rate of IpHA. [source] The structure of phosphate-bound Escherichia coli adenylosuccinate lyase identifies His171 as a catalytic acidACTA CRYSTALLOGRAPHICA SECTION F (ELECTRONIC), Issue 9 2009Guennadi Kozlov Adenylosuccinate lyase (ASL) is an enzyme from the purine-biosynthetic pathway that catalyzes the cleavage of 5-aminoimidazole-4-(N -succinylcarboxamide) ribonucleotide (SAICAR) to 5-aminoimidazole-4-carboxamide ribonucleotide (AICAR) and fumarate. ASL is also responsible for the conversion of succinyladenosine monophosphate (SAMP) to adenosine monophosphate (AMP) and fumarate. Here, the crystal structure of adenylosuccinate lyase from Escherichia coli was determined to 1.9,Ĺ resolution. The enzyme adopts a substrate-bound conformation as a result of the presence of two phosphate ions bound in the active site. Comparison with previously solved structures of the apoenzyme and an SAMP-bound H171A mutant reveals a conformational change at His171 associated with substrate binding and confirms the role of this residue as a catalytic acid. [source] | |||||||||||||||||||