Nuclear-magnetic-resonance study of the conformation of a dinucleotide in solution using the lanthanide probe method.
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The conformation of the dinucleotide adenylyl(3'-5')adenosine 2'-phosphate (ApA2'p) in aqueous solution at different pH values and temperatures has been studied using the lanthanide(III) ethylenodiaminetetraacetate(EDTA) 1:1 complexes as shift and relaxation probes. The conformational analysis, based on mixing different conformations in fast exchange within the nuclear magnetic resonance time scale, agrees well with the results from vicinal coupling constants and dimerization shifts obtained for the metal-free system. The dinucleotide exists in a temperature-dependent and pH-dependent conformational equilibrium between unstacked and base-stacked forms. At neutral pH and low temperature, the stacked form predominates, and it is a predominantly right helical structure, characterized as an anti, 3E, g-, g- g-, g'g', gg, 3E, anti conformation. This situation contrasts with adenylyl(3'-5')adenosine (ApA), where both right and left helices contribute to the stacked form. The nucleotidyl units of the unstacked form of ApA2'p have average conformations which are very similar to those of the corresponding mononucleotides in similar conditions. (+info)
Lanthanide ions induce hydrolysis of hemoglobin-bound 2,3-diphosphoglycerate (2,3-DPG), conformational changes of globin and bidirectional changes of 2,3-DPG-hemoglobin's oxygen affinity.
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The changes in structure and function of 2,3-diphosphoglycerate-hemoglobin (2,3-DPG-Hb) induced by Ln(3+) binding were studied by spectroscopic methods. The binding of lanthanide cations to 2,3-DPG is prior to that to Hb. Ln(3+) binding causes the hydrolysis of either one from the two phosphomonoester bonds in 2,3-DPG non-specifically. The results using the ultrafiltration method indicate that Ln(3+) binding sites for Hb can be classified into three categories: i.e. positive cooperative sites (N(I)), non-cooperative strong sites (N(S)) and non-cooperative weak sites (N(W)) with binding constants in decreasing order: K(I)>K(S)>K(W). The total number of binding sites amounts to about 65 per Hb tetramer. Information on reaction kinetics was obtained from the change of intrinsic fluorescence in Hb monitored by stopped-flow fluorometry. Fluctuation of fluorescence dependent on Ln(3+) concentration and temperature was observed and can be attributed to the successive conformational changes induced by Ln(3+) binding. The results also reveal the bidirectional changes of the oxygen affinity of Hb in the dependence on Ln(3+) concentration. At the range of [Ln(3+)]/[Hb]<2, the marked increase of oxygen affinity (P(50) decrease) with the Ln(3+) concentration can be attributed to the hydrolysis of 2,3-DPG, while the slight rebound of oxygen affinity in higher Ln(3+) concentration can be interpreted by the transition to the T-state of the Hb tetramer induced by Ln(3+) binding. This was indicated by the changes in secondary structure characterized by the decrease of alpha-helix content. (+info)
Composition, characteristic and activity of rare earth element-bound polysaccharide from tea.
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The compositions and structural characteristics of rare earth elements-bound polysaccharides from tea (REE-TPS) were studied with the methods of Inductively Coupled Plasma Mass Spectrometry (ICP-MS), Gas Chromatography (GC) and Extended X-ray Absorption Fine Structure (EXAFS) spectroscopy. The results show that polysaccharide from tea (TPS) was a sort of glycoprotein and coordinated with Rare Earth Elements (REE) closely. The sugar fraction was composed of Rha, Ara, Xyl, Fuc, Glc, and Gal. There existed almost all natural amino acids with Glx, Asx, and Hyp as the major parts in the protein fraction. The REEs in REE-TPS were mainly composed of La, Ce, and Nd, especially, more than 75% of them was La. The coordination atom of the first coordination shell of La in REE-TPS was oxygen, the coordination number of which was 6, and the average distance between the atoms was 2.52 A. The second shell was formed from sulfur atoms, the coordination number and the average distance were 3 and 2.91 A, respectively. The bio-experiments show that REE-TPS could decrease the content of blood glucose in mice significantly. (+info)
Rare earth metal trifluoromethanesulfonates catalyzed benzyl-etherification.
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Rare earth metal trifluoromethanesulfonates [rare earth metal triflate, RE(OTf)3] were found to be efficient catalyst for benzyl-etherification. In the presence of a catalytic amount of RE(OTf)3, condensation of benzyl alcohols and aliphatic alcohols proceeded smoothly to afford the benzyl ethers. The condensation between benzyl alcohols and thiols also proceeded, and thio ethers were obtained in good yield. In these reactions, RE(OTf)3 could be recovered easily after the reactions were completed and could be reused without loss of activity. (+info)
Discoidal impressions and trace-like fossils more than 1200 million years old.
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The Stirling Range Formation of southwestern Australia contains discoidal impressions and trace-like fossils in tidal sandstones. The various disks have previously been linked to the Ediacaran biota, younger than 600 million years old. From this unit, we report U-Th-Pb geochronology of detrital zircon and monazite, as well as low-grade metamorphic monazite, constraining the depositional age to between 2016 +/- 6 and 1215 +/- 20 million years old. Although nonbiological origins for the discoidal impressions cannot be completely discounted, the structures resembling trace fossils clearly have a biological origin and suggest the presence of vermiform, mucus-producing, motile organisms. (+info)
Validity of specifically applied rare earth elements and compartmental models for estimating flux of undigested plant tissue residues through the gastrointestinal tract of ruminants.
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The validity of using rare earth elements as flow markers of undigested residues was evaluated by comparing mean gastrointestinal residence time (GMRT) of rare earths specifically applied to cottonseed hulls (CSH) to that of the indigestible fiber of CSH. Feces were collected from five lambs fed a mineral supplemented diet of CSH containing 52 g CP/kg DM and five lambs fed a CSH plus cottonseed meal diet (CSH+CSM) containing 123 g CP/kg DM. Rare earth elements (La, Yb, and Tb) specifically bound to CSH were included in the diet for a 5-d period and then deleted from the diet for a 3-d period. Following the last fecal collection, lambs were slaughtered for collection of digesta from segments of the gastrointestinal tract. Potentially indigestible NDF (PIF) was determined in diets and digesta from each segment of the gastrointestinal tract. Mean turnover rate, time delay, and GMRT for each rare earth element was estimated by fitting an age-dependent compartment model to profiles of markers appearing in the feces (compartmental model-marker method, CMM). The GMRT also was computed by the indigestible entity pool dilution method (IEPD) as grams of PIF in sampled segment/mean intake rate of PIF proceeding slaughter, g/h. The GMRT computed by the CMM and the IEPD methods did not significantly (P < 0.05) differ (99.6 vs 94.8 h and 58.9 vs 59.5 h for CMM vs IEPD and CSH and CSH+CSM diets, respectively). Regression of GMRT estimated for rare earths vs PIF yielded a highly significant regression (P = 0.001) with a regression coefficient of 0.94 +/- 0.016. It was concluded that rare earth elements applied to specific feeds are valid flow markers for the undigested residues derived from such marked feeds. (+info)
An analysis of the action of cations of the lanthanide series on the mechanical responses of guinea-pig ileal longitudinal muscle.
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1. The inhibitory effects of lanthanide cations (Ln3+) on mechanical responses and 45Ca uptake in guinea-pig ileal longitudinal smooth muscle were studied. 2. Ln3+ strongly inhibited the phasic and tonic component of the response to the muscarinic agonist cis-2-methyl-4-dimethylaminomethyl-1,3-dioxolane methiodide (CD) the two components being affected to the same extent. Inhibition was also obtained for the responses evoked by high K+ but here the effect was mainly on the phasic response, the tonic component was merely delayed. 3. Other members of the Ln3+ series, with the exception of cerium, were found to be more effective than lanthanum in their ability to inhibit the CD response. Thulium, Tm3+, the thirteenth member of the series was the most effective cation. 4. Analysis of 170Tm uptake revealed at least two components. The concentration-dependence of one component, saturating at 2-5 x 10(-6) Tm, corresponded closely to that of the inhibitory effect of Tm3+ on contraction. 5. 170Tm uptake as a function of time showed a secondary rise after 30 min of exposure to the lanthanide. 6. Although 2-5 x 10(-6) M-Tm3+ produced 90% inhibition of the CD and the high K+ induced responses significant reduction of 45Ca uptake by the muscle was only detected when much higher Tm3+ concentrations (greater than or equal 10(-3) M-Tm3+) were used. 7. It is concluded that Ln3+ combine with membrane sites specifically involved in Ca2+ translocation during excitation-contraction coupling. (+info)
Rare earth-doped glass microbarcodes.
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The development of ultraminiaturized identification tags has applications in fields ranging from advanced biotechnology to security. This paper describes micrometer-sized glass barcodes containing a pattern of different fluorescent materials that are easily identified by using a UV lamp and an optical microscope. A model DNA hybridization assay using these "microbarcodes" is described. Rare earth-doped glasses were chosen because of their narrow emission bands, high quantum efficiencies, noninterference with common fluorescent labels, and inertness to most organic and aqueous solvents. These properties and the large number (>1 million) of possible combinations of these microbarcodes make them attractive for use in multiplexed bioassays and general encoding. (+info)