148,117 research outputs found
SPECIFIC RECOGNITION OF N-ACETYLNEURAMINIC ACID IN THE G(M2) EPITOPE BY HUMAN G(M2) ACTIVATOR PROTEIN
No full textG(M2) Activator is a low molecular weight protein cofactor that stimulates the enzymatic conversion of G(M2) into G(M3) by human beta-hexosaminidase A and also the conversion of G(M2) into G(A2) by clostridial sialidase (Wu, Y.-Y., Lockyer, J. M., Sugiyama, E., Pavlova, N. V., Li, Y.-T., and Li, S.- C. (1994) J. Biol. Chem. 269, 16276-16283). Among the five known activator proteins for the enzymatic hydrolysis of glycosphingolipids, only G(M2) activator is effective in stimulating the hydrolysis of G(M2). However, the mechanism of action of G(M2) activator is still not well understood, Using a unique disialosylganglioside, GalNAc-G(D1a), as the substrate, we were able to show that in the presence of G(M2) activator, GalNAc-G(D1a) was specifically converted into GalNAc-G(M1a) by clostridial sialidase, while in the presence of saposin B, a nonspecific activator protein, GalNAc-G(D1a) was converted into both GalNAc-G(M1a) and GalNAc-G(M1b). individual products generated from GalNAc-G(D1a) by clostridial sialidase were identified by thin layer chromatography, negative secondary ion mass spectrometry, and immunostaining with a monoclonal IgM that recognizes the G(M2) epitope. Our results clearly show that G(M2) activator recognizes the G(M2) epitope in GalNAc-G(D1a). Thus, G(M2) activator may interact with the trisaccharide structure of the G(M2) epitope and render the GalNAc and NeuAc residues accessible to beta-hexosaminidase A and sialidase, respectively
A new structure of Nd1+?Fe4B4 phase in NdFeB magnet
No full textA new structure for Nd1+eFe4B4 phase has been observed, which has the same structure as Gd1+eFe4B4. The compound has Pccn structure with a = 0.71 nm and c = 2.74 nm, and its composition was found to be Nd2Fe7B7
Characterization of an alternatively spliced G(M2) activator protein, G(M2A) protein - An activator protein which stimulates the enzymatic hydrolysis of N-acetylneuraminic acid, but not N-acetylgalactosamine, from G(M2)
No full textG(M2) activator protein is a protein cofactor which stimulates the enzymatic hydrolysis of both GalNAc and NeuAc from G(M2). We have previously isolated two cDNA clones, G(M2) activator cDNA and G(M2A) cDNA, for human G(M2) activator protein (Nagarajan, S., Chen, H.-C., Li, S.-C., Li, Y.-T., and Lockyer, J. M. (1992) Biochem. J. 282, 807-813). G(M2A) mRNA is an RNA alternative splicing product that contains exons 1, 2, 3, and intron 3 of the genomic DNA sequence of G(M2) activator protein (Klima, H., Tanaka, A., Schnabel, D., Nakano, T., Schroder, M., Suzuki, K., and Sandhoff, K. (1991) FEES Left. 289, 260-264). G(M2A) cDNA encodes a protein (G(M2A) protein) containing 1-109 of the 160 amino acids of human G(M2) activator protein, plus a tripeptide (VST) encoded by intron 3 at the COOH terminus. Thus, G(M2A) protein can be regarded as a form (truncated version) of G(M2) activator protein. We have expressed G(M2A) cDNA in Escherichia coli using pT7-7 as the vector. The recombinant G(M2A) protein was purified to an electrophoretically homogeneous form and was found to stimulate the hydrolysis of NeuAc from G(M2) by clostridial sialidase, but not the hydrolysis of GalNAc from G(M2) by beta-hexosaminidase A. Like G(M2) activator protein, G(M2A) protein also specifically recognized the terminal G(M2) epitope in GalNAc-GD1a and stimulated the hydrolysis of only the external NeuAc from this ganglioside by clostridial sialidase. These results enabled us to discern the enzymatic hydrolyses of GalNAc and NeuAc from the G(M2) epitope and established that the NeuAc recognition domain of G(M2) activator protein is located within amino acids 1-109. The presence of G(M2A) mRNA in human tissues and the selective stimulation of NeuAc hydrolysis by G(M2A) protein indicate that this activator protein may be involved in the catabolism of G(M2) through the asialo-G(M2) pathway
GABI-Kat SimpleSearch: an Arabidopsis thaliana T-DNA mutant database with detailed information for confirmed insertions
No full textLi Y, Rosso MG, Viehöver P, Weisshaar B. GABI-Kat SimpleSearch: an Arabidopsis thaliana T-DNA mutant database with detailed information for confirmed insertions. Nucleic Acids Research. 2007;35(Database):D874-D878
Li–Yorke and distributionally chaotic operators
No full textWe study Li-Yorke chaos and distributional chaos for operators on Banach spaces. More precisely, we characterize Li-Yorke chaos in terms of the existence of irregular vectors. Sufficient "computable" criteria for distributional and Li-Yorke chaos are given, together with the existence of dense scrambled sets under some additional conditions. We also obtain certain spectral properties. Finally, we show that every infinite dimensional separable Banach space admits a distributionally chaotic operator which is also hypercyclic. © 2010 Elsevier Inc.The second author is supported in part by MEC and FEDER, Project MTM2008-05891. The third and fourth authors are supported in part by MEC and FEDER, Projects MTM2007-64222, MTM2010-14909 and by Generalitat Velenciana. Project PROMETEO/2008/101. We want to thank the referee for the suggestions.Bermúdez, T.; Bonilla, A.; Martínez Jiménez, F.; Peris Manguillot, A. (2011). Li–Yorke and distributionally chaotic operators. Journal of Mathematical Analysis and Applications. 373:83-93. https://doi.org/10.1016/j.jmaa.2010.06.011S839337
Low-energy excitations in the electron-doped metal phtalocyanine LiO.5MnPc from Li and 1H NMR
No full textNMR and magnetization measurements in Li0.5MnPc (Pc=C32H16N8), recently proposed as a strongly correlated metal, are presented. Two different low-frequency dynamics are evidenced. The first one, probed by 1H nuclei, gives rise to a slowly relaxing magnetization at low temperature and is associated with the freezing of MnPc S=3/2 spins. This dynamics is similar to the one observed in pristine beta-MnPc and originates from Li-depleted chain segments. The second one, evidenced by the 7Li spin-lattice relaxation rate, is associated with the hopping of the electrons along Li-rich chains. The characteristic correlation times for the two dynamics are derived, and the role of the disorder is briefly discussed
Pleurospermum tripartitum sp nov (Umbelliferae) from western Yunnan, China
No full textPleurospermum tripartitum Pu, R. Li & H. Li, a new species of Umbelliferae from western Yunnan, China, is described and illustrated. It is closely similar to P. macrochlaenum K. T. Fu & Y. C. Ho, but differs by having unbranched stem, conspicuous calyx teeth, and white petals
A Study of the Thermodynamics and Kinetics of LiₓFePO₄ as a Cathode Material for Li Batteries
No full textOlivine-type LiFePO4 has been recognized as one of the most promising cathode materials for rechargeable Li batteries. Its advantages include high capacity, high stability, nontoxicity, and low cost. Our methods for synthesizing nanocrystalline LixFePO4 with the olivine structure are described. Solid-state reactions and precipitation reactions were both successful, and ball milling was especially effective at reducing crystallite sizes. Diffractometry and microscopy were used to characterize these materials, and results of impurity phases, excess Fe3+, and internal stresses are reported for the different types of synthesis.
Applications of lithium-ion batteries, including automotive applications, require fast kinetics and high conductivity of ions and electrons. Unfortunately, LixFePO4 has the electronic structure of an insulator, an entirely unsatisfactory situation if it is to be used as a battery electrode. Electrical conductivity in LixFePO4 occurs by the motion of small polarons, which are valence electrons at Fe atoms plus their distorted local environments. Electrical conductivity of LixFePO4 is interpreted in terms of small polaron hopping. There are other factors of importance in these measurements, such as impurities or defects that block the one-dimensional conduction channels of the olivine structure of LixFePO4.
We studied the polaron hopping directly, which allows us to understand the intrinsic electrical conductivity, and how it depends on microstructure and composition of LixFePO4. The experimental technique was Mossbauer spectrometry, which has been used for many years as a means for determining the fractions of Fe2+ and Fe3+ in a material. Usually the spectral signatures of Fe2+ and Fe3+ are distinct. When valence electrons hop between Fe2+ and Fe3+ at a frequency of 108 Hz or higher, however, the valence changes during the timescale of the Mossbauer measurement and the spectrum is blurred. By measuring Mossbauer spectra at elevated temperatures, we can determine the fractions of Fe atoms participating in polaron hopping, and determine the activation energy of the process. From this we estimate intrinsic electrical conductivities of 10-7S/cm at room temperature for nanocrystalline Li0.5FePO4, for example. We find a comparable conductivity for LixFePO4 prepared as a solid solution, but the conductivity of conventional LixFePO4 is much lower.
There has been much discussion about how surface area might thermodynamically stabilize the solid solution phase of nanocrystalline LixFePO4. In a series of X-ray diffraction measurements, some at elevated temperatures, we found the solid solution phase of LixFePO4 to be especially robust at room temperature when the material was prepared in nanocrystalline form. Moreover, the consistent phase transition temperature around 200°C was observed, as evidence for the unchanged equilibrium phase diagram by crystallite size. This is consistent with our evaluation on the boundaries of the two-phase mixture of triphylite and heterosite during Li insertion and extraction. Profiles of entropy and enthalpy changes were evaluated by open-circuit voltage measurements. The boundaries were found at x=0.05 and 0.95 in the LixFePO4 with crystal size of 70 nm, similar to the reported values on bulk-LixFePO4. These are important in practice, because electrochemical lithiation and delithiation at room temperature should remain as a two-phase transformation, even if a solid solution of lithium is present in the initial electrode material.</p
Compressible Rayleigh-Taylor turbulent mixing under different acceleration histories
No full textCompressible Rayleigh-Taylor turbulent mixing (CRTM) induced by Rayleigh-Taylor instability occurs when a compressible fluid of heavy density is accelerated or supported against gravity by a compressible fluid of light density, and is of fundamental importance in applications from combustion, to inertial confinement fusion, and to astrophysics. Traditionally, CRTFs are studied under constant acceleration histories. Due to the nature of the processes, however, it is necessary to study CRTF under general acceleration histories g(t). In this aspect, the evolution of Rayleigh-Taylor turbulent mixing under complex acceleration histories, including changes in signs, have been studied numerically[1] and experimentally[2] for incompressible flows, leaving an open question on that of compressible flows. In fact, most engineering problems are compressible. In addition, the available engineering turbulence models cannot capture the variation of mixing width for CRTM with complex acceleration histories, such as the gravity reversal. In order to better understanding the dynamic of CRTM under different variation histories, several DNS cases with different acceleration histories have been conducted and analyzed
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