Your browser doesn't support javascript.
Mostrar: 20 | 50 | 100
Resultados 1 - 18 de 18
Filtrar
Mais filtros










Base de dados
Intervalo de ano de publicação
1.
Nature ; 581(7806): 89-93, 2020 05.
Artigo em Inglês | MEDLINE | ID: mdl-32376953

RESUMO

Small interfering RNAs (siRNAs) are essential for proper development and immunity in eukaryotes1. Plants produce siRNAs with lengths of 21, 22 or 24 nucleotides. The 21- and 24-nucleotide species mediate cleavage of messenger RNAs and DNA methylation2,3, respectively, but the biological functions of the 22-nucleotide siRNAs remain unknown. Here we report the identification and characterization of a group of endogenous 22-nucleotide siRNAs that are generated by the DICER-LIKE 2 (DCL2) protein in plants. When cytoplasmic RNA decay and DCL4 are deficient, the resulting massive accumulation of 22-nucleotide siRNAs causes pleiotropic growth disorders, including severe dwarfism, meristem defects and pigmentation. Notably, two genes that encode nitrate reductases-NIA1 and NIA2-produce nearly half of the 22-nucleotide siRNAs. Production of 22-nucleotide siRNAs triggers the amplification of gene silencing and induces translational repression both gene specifically and globally. Moreover, these 22-nucleotide siRNAs preferentially accumulate upon environmental stress, especially those siRNAs derived from NIA1/2, which act to restrain translation, inhibit plant growth and enhance stress responses. Thus, our research uncovers the unique properties of 22-nucleotide siRNAs, and reveals their importance in plant adaptation to environmental stresses.


Assuntos
Aclimatação/genética , Arabidopsis/genética , Regulação da Expressão Gênica de Plantas , Biossíntese de Proteínas/genética , RNA de Plantas/genética , RNA Interferente Pequeno/genética , Arabidopsis/crescimento & desenvolvimento , Proteínas de Arabidopsis/genética , Proteínas de Arabidopsis/metabolismo , Proteínas Argonauta/metabolismo , Proteínas de Ciclo Celular , Inativação Gênica , Mutação , Nitrato Redutase/genética , Doenças das Plantas/genética , Estabilidade de RNA , RNA Mensageiro/genética , RNA Interferente Pequeno/biossíntese , Ribonuclease III/metabolismo
2.
Sci Total Environ ; 682: 541-552, 2019 Sep 10.
Artigo em Inglês | MEDLINE | ID: mdl-31129542

RESUMO

A three-dimensional variational (3DVAR) lidar data assimilation method is developed based on the Community Radiative Transfer Model (CRTM) and Weather Research and Forecasting model coupled to Chemistry (WRF-Chem) model. A 3DVAR data assimilation (DA) system using lidar extinction coefficient observation data is established, and variables from the Model for Simulating Aerosol Interactions and Chemistry (MOSAIC) mechanism of the WRF-Chem model are employed. Hourly lidar extinction coefficient data from 12:00 to 18:00 UTC on March 13, 2018 at four stations in Beijing are assimilated into the initial field of the WRF-Chem model; subsequently, a 24 h PM2.5 concentration forecast is made. Results indicate that assimilating lidar data can effectively improve the subsequent forecast. PM2.5 forecasts without using lidar DA are remarkably underestimated, particularly during heavy haze periods; in contrast, forecasts of PM2.5 concentrations with lidar DA are closer to observations, the model low bias is evidently reduced, and the vertical distribution of the PM2.5 concentration in Beijing is distinctly improved from the surface to 1200 m. Of the five aerosol species, improvements of NO3- are the most significant. The correlation coefficient between PM2.5 concentration forecasts with lidar DA and observations at 12 stations in Beijing is increased by 0.45, and the corresponding average RMSE is decreased by 25 µg·m-3, which respectively compared to those without DA.

3.
Mol Genet Genomic Med ; 7(3): e554, 2019 03.
Artigo em Inglês | MEDLINE | ID: mdl-30623608

RESUMO

BACKGROUND: Globally, colon cancer (CC) is the third reason of tumor-related deaths. Previous reports indicate that Forkhead box O3 (FOXO3) is involved in the development of various tumors and may have different effects depending upon the types of tumors. Hence, this study was to examine the effects of FOXO3 on CC cells and uncover the possible mechanisms. METHODS: MTT and cell count assay were applied to analyze the viability of transfected CC cells. rVista, dual luciferase reporter assay, and chromatin immunoprecipitation assay were used to identify the downstream target of FOXO3 in HCT116 cells. The mRNA and protein abundance of FOXO3 and MDR1 were determined by quantitative PCR and Western blot, respectively. RESULTS: Forkhead box O3 stimulated the proliferation of both HCT116 and DLD1 cells. Moreover, FOXO3 overexpression inhibited doxorubicin sensitivity of HCT116 cells, while the knockout of FOXO3 by FOXO3 shRNA restored the doxorubicin sensitivity in doxorubicin-resistant HCT116 DR cells. Next, we found that FOXO3 directly bound to the promoter of MDR1 and enhanced MDR1 expression in HCT116 cells. MDR1 overexpression enhanced the viability and doxorubicin resistance of CC cells. Besides, MDR1 overexpression plasmid significantly abrogated the decrease in cell proliferation and resistance of HCT116 cells to doxorubicin caused by FOXO3 knockout. CONCLUSION: Forkhead box O3 exhibited promotive effects on the proliferation and doxorubicin resistance in CC cells via targeting MDR1.


Assuntos
Neoplasias do Colo/metabolismo , Resistencia a Medicamentos Antineoplásicos , Proteína Forkhead Box O3/metabolismo , Subfamília B de Transportador de Cassetes de Ligação de ATP/genética , Subfamília B de Transportador de Cassetes de Ligação de ATP/metabolismo , Proliferação de Células/efeitos dos fármacos , Proliferação de Células/genética , Doxorrubicina/farmacologia , Proteína Forkhead Box O3/genética , Regulação Neoplásica da Expressão Gênica , Células HCT116 , Humanos
4.
Sci Rep ; 8(1): 14422, 2018 09 26.
Artigo em Inglês | MEDLINE | ID: mdl-30258105

RESUMO

The current application of genome editing to crop plants is limited to cultivars that are amenable to in vitro culture and regeneration. Here, we report an in planta genome-editing which does not require callus culture and regeneration. Shoot apical meristems (SAMs) contain a subepidermal cell layer, L2, from which germ cells later develop during floral organogenesis. The biolistic delivery of gold particles coated with plasmids expressing CRISPR/Cas9 components designed to target TaGASR7 were bombarded into SAM-exposed embryos of imbibed seeds. Bombarded embryos showing transient GFP expression within SAM were selected and grown into adult plants. Mutations in the target gene were assessed in fifth-leaf tissue by cleaved amplified polymorphic sequence analysis. Eleven (5.2%) of the 210 bombarded plants carried mutant alleles, and the mutations of three (1.4%) of these were inherited in the next generation. Genotype analysis of T1 plants identified plants homozygous for the three homeologous genes, which were all derived from one T0 plant. These plants showed no detectable integration of the Cas9 and guide RNA genes, indicating that transient expression of CRISPR/Cas9 introduced the mutations. Together, our current method can be used to achieve in planta genome editing in wheat using CRISPR/Cas9 and suggests possible applications to other recalcitrant plant species and variations.


Assuntos
Biolística/métodos , Sistemas CRISPR-Cas , Edição de Genes/métodos , Triticum/genética , Meristema/genética , Mutagênese , Mutação , Plantas Geneticamente Modificadas/genética , RNA Guia/genética
5.
Front Plant Sci ; 9: 125, 2018.
Artigo em Inglês | MEDLINE | ID: mdl-29472942

RESUMO

Ribosome biogenesis is a highly complex process that requires several cofactors, including DExD/H-box RNA helicases (RHs). RHs are a family of ATPases that rearrange the secondary structures of RNA and thus remodel ribonucleoprotein complexes. DExD/H-box RHs are found in most organisms and play critical roles in a variety of RNA-involved cellular events. In human and yeast cells, many DExD/H box RHs participate in multiple steps of ribosome biogenesis and regulate cellular proliferation and stress responses. In plants, several DExD/H-box RHs have been demonstrated to be associated with plant development and abiotic stress tolerance through their functions in modulating pre-rRNA processing. In this review, we summarize the pleiotropic roles of DExD/H-box RHs in rRNA biogenesis and other biological functions. We also describe the overall function of the DExD/H-box RH family in ribosome biogenesis based on data from human and yeast.

6.
Biosens Bioelectron ; 90: 39-45, 2017 Apr 15.
Artigo em Inglês | MEDLINE | ID: mdl-27871048

RESUMO

A novel non-enzymatic superoxide anion (O2•-) sensor was fabricated based on Ag nanoparticles (NPs)/L-cysteine functioned carbon nanotubes (Cys-MWCNTs) nanocomposites and used to measure the release of O2•- from living cells. In this strategy, AgNPs could be uniformly electrodeposited on the MWCNTs surface with average diameter of about 20nm as exhibited by scanning electronmicroscopy (SEM). Electrochemical study demonstrated that the AgNPs/Cys-MWCNTs modified glassy carbon electrode exhibited excellent catalytic activity toward the reduction of O2•- with a super wide linear range from 7.00×10-11 to 7.41×10-5M and a low detection limit (LOD) of 2.33×10-11M (S/N=3). Meanwhile, the mechanism for O2•- reduction was also proposed for the first time. Importantly, this novel non-enzymatic O2•- sensor can detect O2•- release from cancer cells under both the external stimulation and the normal condition, which has the great potential application in clinical diagnostics to assess oxidative stress of living cells.


Assuntos
Técnicas Biossensoriais/métodos , Nanopartículas Metálicas/química , Neoplasias/diagnóstico , Superóxidos/isolamento & purificação , Cisteína/química , Humanos , Peróxido de Hidrogênio/química , Nanocompostos/química , Nanotubos de Carbono/química , Neoplasias/patologia , Estresse Oxidativo/genética , Prata/química , Superóxidos/química
7.
Biosens Bioelectron ; 86: 671-676, 2016 Dec 15.
Artigo em Inglês | MEDLINE | ID: mdl-27471158

RESUMO

8-Hydroxy-2'-deoxyguanosine (8-OHdG) is commonly identified as a biomarker of oxidative DNA damage. In this work, a novel and facile 8-OHdG sensor was developed based on the multi-walled carbon nanotubes (MWCNTs) modified glassy carbon electrode (GCE). It exhibited good electrochemical responses toward the oxidation of 8-OHdG, and the linear ranges were 5.63×10(-8)-6.08×10(-6)M and 6.08×10(-6)-1.64×10(-5)M, with the detection limit of 1.88×10(-8)M (S/N=3). Moreover, the fabricated sensor was applied for the determination of 8-OHdG generated from damaged DNA and guanine, respectively, and the oxidation currents of 8-OHdG increased along with the damaged DNA and guanine within certain concentrations. These results could be used to evaluate the DNA damage, and provide useful information on diagnosing diseases caused by mutation and deficiency of the immunity system.


Assuntos
Condutometria/instrumentação , Dano ao DNA/genética , DNA/genética , Desoxiguanosina/análogos & derivados , Guanina/química , 8-Hidroxi-2'-Desoxiguanosina , DNA/análise , Desoxiguanosina/química , Desoxiguanosina/genética , Eletrodos , Desenho de Equipamento , Análise de Falha de Equipamento , Guanina/análise , Nanotubos de Carbono/química , Oxirredução , Estresse Oxidativo , Reprodutibilidade dos Testes , Sensibilidade e Especificidade
8.
PLoS One ; 11(4): e0154040, 2016.
Artigo em Inglês | MEDLINE | ID: mdl-27116354

RESUMO

DEAD-box RNA helicases comprise a large family and are involved in a range of RNA processing events. Here, we identified one of the Arabidopsis thaliana DEAD-box RNA helicases, AtRH7, as an interactor of Arabidopsis COLD SHOCK DOMAIN PROTEIN 3 (AtCSP3), which is an RNA chaperone involved in cold adaptation. Promoter:GUS transgenic plants revealed that AtRH7 is expressed ubiquitously and that its levels of the expression are higher in rapidly growing tissues. Knockout mutant lines displayed several morphological alterations such as disturbed vein pattern, pointed first true leaves, and short roots, which resemble ribosome-related mutants of Arabidopsis. In addition, aberrant floral development was also observed in rh7 mutants. When the mutants were germinated at low temperature (12°C), both radicle and first leaf emergence were severely delayed; after exposure of seedlings to a long period of cold, the mutants developed aberrant, fewer, and smaller leaves. RNA blots and circular RT-PCR revealed that 35S and 18S rRNA precursors accumulated to higher levels in the mutants than in WT under both normal and cold conditions, suggesting the mutants are partially impaired in pre-rRNA processing. Taken together, the results suggest that AtRH7 affects rRNA biogenesis and plays an important role in plant growth under cold.


Assuntos
Aclimatação , Proteínas de Arabidopsis/metabolismo , Arabidopsis/crescimento & desenvolvimento , RNA Helicases DEAD-box/metabolismo , Regulação da Expressão Gênica de Plantas , Proteínas de Choque Térmico/metabolismo , Arabidopsis/genética , Arabidopsis/fisiologia , Proteínas de Arabidopsis/genética , Temperatura Baixa , RNA Helicases DEAD-box/genética , Regulação da Expressão Gênica no Desenvolvimento , Técnicas de Inativação de Genes , Germinação , Proteínas de Choque Térmico/genética , Mutação , Filogenia , Plantas Geneticamente Modificadas/genética , Plantas Geneticamente Modificadas/crescimento & desenvolvimento , Plantas Geneticamente Modificadas/metabolismo , Mapas de Interação de Proteínas , Precursores de RNA/genética , Precursores de RNA/metabolismo , RNA de Plantas/genética , RNA de Plantas/metabolismo
9.
Plant Signal Behav ; 10(8): e1042637, 2015.
Artigo em Inglês | MEDLINE | ID: mdl-26252779

RESUMO

Cold shock domain (CSD) proteins are RNA chaperones that destabilize RNA secondary structures. Arabidopsis Cold Shock Domain Protein 2 (AtCSP2), one of the 4 CSD proteins (AtCSP1-AtCSP4) in Arabidopsis, is induced during cold acclimation but negatively regulates freezing tolerance. Here, we analyzed the function of AtCSP2 in salt stress tolerance. A double mutant, with reduced AtCSP2 and no AtCSP4 expression (atcsp2-3 atcsp4-1), displayed higher survival rates after salt stress. In addition, overexpression of AtCSP2 resulted in reduced salt stress tolerance. These data demonstrate that AtCSP2 acts as a negative regulator of salt stress tolerance in Arabidopsis.


Assuntos
Proteínas de Arabidopsis/genética , Arabidopsis/genética , Proteínas e Peptídeos de Choque Frio/genética , Regulação da Expressão Gênica de Plantas , RNA de Plantas/metabolismo , Proteínas de Ligação a RNA/genética , Tolerância ao Sal/genética , Cloreto de Sódio/metabolismo , Arabidopsis/metabolismo , Proteínas de Arabidopsis/metabolismo , Proteínas e Peptídeos de Choque Frio/metabolismo , Temperatura Baixa , Perfilação da Expressão Gênica , Genes de Plantas , Chaperonas Moleculares/metabolismo , Proteínas de Ligação a RNA/metabolismo
10.
Plant Physiol Biochem ; 84: 251-260, 2014 Nov.
Artigo em Inglês | MEDLINE | ID: mdl-25306528

RESUMO

A novel cold-inducible GSK3/shaggy-like kinase, TaSK5, was isolated from winter wheat using a macroarray-based differential screening approach. TaSK5 showed high similarity to Arabidopsis subgroup I GSK3/shaggy-like kinases ASK-alpha, AtSK-gamma and ASK-epsilon. RNA gel blot analyses revealed TaSK5 induction by cold and NaCl treatments and to a lesser extent by drought treatment. TaSK5 functionally complemented the cold- and salt-sensitive phenotypes of a yeast GSK3/shaggy-like kinase mutant, △mck1. Transgenic Arabidopsis plants overexpressing TaSK5 cDNA showed enhanced tolerance to salt and drought stresses. By contrast, the tolerance of the transgenic plants to freezing stress was not altered. Microarray analysis revealed that a number of abiotic stress-inducible genes were constitutively induced in the transgenic Arabidopsis plants, suggesting that TaSK5 may function in a novel signal transduction pathway that appears to be unrelated to DREB1/CBF regulon and may involve crosstalk between abiotic and hormonal signals.


Assuntos
Arabidopsis/efeitos dos fármacos , Arabidopsis/metabolismo , Secas , Plantas Geneticamente Modificadas/efeitos dos fármacos , Plantas Geneticamente Modificadas/metabolismo , Cloreto de Sódio/farmacologia , Triticum/enzimologia , Arabidopsis/genética , Proteínas de Arabidopsis/genética , Proteínas de Arabidopsis/metabolismo , Regulação da Expressão Gênica de Plantas/efeitos dos fármacos , Regulação da Expressão Gênica de Plantas/genética , Plantas Geneticamente Modificadas/genética , Triticum/genética
11.
Mol Cell Biochem ; 362(1-2): 141-8, 2012 Mar.
Artigo em Inglês | MEDLINE | ID: mdl-22045061

RESUMO

MicroRNAs (miRNAs) are increasingly reported to have important roles in diverse biological and pathological processes. Changes in abundance of muscle-specific microRNA, miR-1, have been implicated in cardiac disease, including arrhythmia and heart failure. However, the specific molecular targets and cellular mechanisms involved in the miR-1 function in the heart are only beginning to emerge. In this study, we investigated miR-1 expression and its potential role in the mouse model of viral myocarditis (VMC). The expression levels of miR-1 and its target gene Connexin 43 (Cx43) were measured by real-time PCR and western blotting, respectively. The miR-1 expression levels were significantly increased in cardiac myocytes from VMC mice in comparison with control samples (relative expression: 10 ± 2.5 vs. 31 ± 7.6, P < 0.05). Among the target genes of miR-1, the expression Cx43 protein was significantly reduced in such mice while there was no significant difference in the its mRNA levels. Our results revealed an inverse correlation between miR-1 levels and Cx43 protein expression in VMC samples. Using a bioinformatics-based approach, we found two identical potential binding sites were found in mouse miR-1 and Cx43 3'- untranslated region, this confirms a possible regulatory role of miR-1. In cultured, miRNA transfected myocardial cells, we show overexpression of miR-1 accompanied by a decrease in Cx43 protein's expression. There was only a slight (not statistically significant) drop in Cx43 mRNA levels. Our results indicate that miR-1 is involved in VMC via post-transcriptional repression of Cx43, and might constitute potentially valuable data for the development of a new approach in the treatment of this disease.


Assuntos
Conexina 43/metabolismo , Infecções por Coxsackievirus/genética , MicroRNAs/genética , Miocardite/genética , Miocardite/virologia , Miócitos Cardíacos/metabolismo , Animais , Células Cultivadas , Conexina 43/genética , Infecções por Coxsackievirus/metabolismo , Enterovirus Humano B , Masculino , Camundongos , Camundongos Endogâmicos BALB C , MicroRNAs/metabolismo , Miocardite/metabolismo , Miócitos Cardíacos/patologia , Miócitos Cardíacos/virologia , RNA Mensageiro/genética , RNA Mensageiro/metabolismo , Ratos
12.
Fa Yi Xue Za Zhi ; 27(1): 5-8, 2011 Feb.
Artigo em Chinês | MEDLINE | ID: mdl-21542217

RESUMO

OBJECTIVE: To explore the relationship between beta-actin mRNA degradation in SD rat's brain, heart and kidney and early postmortem interval (PMI) in order to find new markers for estimating early PMI. METHODS: Rats were sacrificed and kept in the place at a temperature of 20 degrees C. The total RNA were extracted from the brain, heart and kidney at different PMI points. Real time RT-PCR was applied to determine beta-actin mRNA levels in total RNA and the results were given in the form of Ct values. Linear relationships between PMI and Ct values were obtained and the functions of linear regression were established. RESULTS: The great decrease of beta-actin mRNA level were observed in the three organs. The degradation rate was obviously higher in 24 hours after death in the heart and kidney. However, there were no significant changes in the brain. The changes of Ct values and PMI showed a good linear relationship. CONCLUSION: beta-actin mRNA in rat's brain, heart and kidney degrades obviously after death and can be used for estimating early PMI by its degradation rules.


Assuntos
Actinas/metabolismo , Encéfalo/metabolismo , Rim/metabolismo , Miocárdio/metabolismo , Mudanças Depois da Morte , RNA Mensageiro/metabolismo , Actinas/genética , Animais , Medicina Legal/métodos , Masculino , Estabilidade de RNA , RNA Mensageiro/genética , Ratos , Ratos Sprague-Dawley , Reação em Cadeia da Polimerase Via Transcriptase Reversa/métodos , Fatores de Tempo
13.
J Phys Condens Matter ; 23(13): 135501, 2011 Apr 06.
Artigo em Inglês | MEDLINE | ID: mdl-21415475

RESUMO

Employing a first-principles method, we have studied the stability, diffusivity, and permeation properties of hydrogen (H) and its isotopes in bcc vanadium (V). A single H atom is found to favor the tetrahedral interstitial site (TIS) in V. The charge density distribution exhibits a strong interaction between H and its neighbor V atoms. Analysis of DOS and Bader charge reveals that the occupation number of H-induced low energy states is directly associated with the stability of H in V. Further, H is shown to diffuse between the neighboring TISs with a diffusion barrier of 0.07 eV. Diffusion coefficients and permeabilities of H isotopes in V are estimated with empirical theory. At a typical temperature of 800 K, the diffusion coefficient and the permeability of H are 2.48 × 10(-4) cm(2) s(-1) and 2.19 × 10(-9) mol m(-1) s(-1) Pa(- 1/2), respectively.


Assuntos
Hidrogênio/química , Modelos Químicos , Vanádio/química , Difusão , Cinética , Teoria Quântica , Temperatura
14.
Yi Chuan ; 32(6): 571-6, 2010 Jun.
Artigo em Chinês | MEDLINE | ID: mdl-20566460

RESUMO

Bacteria often sequentially utilize coexisting carbohydrates in environment and firstly select the one (frequently glucose) easiest to metabolize. This phenomenon is known as carbon catabolite repression (CCR). In existing Chinese teaching materials of molecular biology and related courses, unclear or even wrong interpretations are given about CCR mechanism. A large number of studies have shown that rather than the existence of intracellular glucose, CCR is mainly caused by the glucose transport process coupling with glucose phosphorylation via the phosphoenolpyruvate: carbohydrate phosphotransferase system PTS. The transport process leads to accumulation of dephosphorylated form of EAGlc.This form of EAGlc can bind the membrane-localized LacY protein to block the uptake of lactose inducer. cAMP functions in activation of key genes involved in PTS system to strengthen the role of inducer exclusion. In addition, dephosphorylated form of EBGlc and Yee bind global transcription repressor Mlc to ensure the expression of key genes involved in the PTS system. This review summarizes the current advancement in mechanism of Escherichia coli carbon catabolite repression.


Assuntos
Metabolismo dos Carboidratos , Escherichia coli/metabolismo , AMP Cíclico/fisiologia , Proteína Receptora de AMP Cíclico/fisiologia , Sistema Fosfotransferase de Açúcar do Fosfoenolpiruvato/fisiologia
15.
J Phys Condens Matter ; 22(44): 445504, 2010 Nov 10.
Artigo em Inglês | MEDLINE | ID: mdl-21403351

RESUMO

We have investigated the structure, solution and diffusion behavior of carbon (C) in tungsten (W) based on first-principles calculations. The single C atom is energetically favorable sitting at the octahedral interstitial site (OIS) with a solution energy of 0.78 eV in W. Double C atoms tend to be paired up at the two neighboring OISs along the (210) direction with a distance of ∼ 3.57 Å and a binding energy of + 0.50 eV. This suggests that a positive attractive interaction between C atoms exists, which might lead to a local higher concentration of C in W and form carbide. Kinetically, the C and vacancy diffusion co-efficients as a function of temperature have been determined, and are 1.32 × 10(-19) m(2) s(-1) and 3.11 × 10(-23) m(2) s(-1) at a typical temperature of 600 K, respectively.

16.
J Phys Condens Matter ; 21(17): 175407, 2009 Apr 29.
Artigo em Inglês | MEDLINE | ID: mdl-21825422

RESUMO

We perform first-principles computational tensile and compressive tests (FPCTT and FPCCT) to investigate the intrinsic bonding and mechanical properties of a γ-TiAl intermetallic compound (L 1(0) structure) using a first-principles total energy method. We found that the stress-strain relations and the corresponding theoretical tensile strengths exhibit strong anisotropy in the [001], [100] and [110] crystalline directions, originating from the structural anisotropy of γ-TiAl. Thus, γ-TiAl is a representative intermetallic compound that includes three totally different stress-strain modes. We demonstrate that all the structure transitions in the FPCTT and FPCCT result from the breakage or formation of bonds, and this can be generalized to all the structural transitions. Furthermore, based on the calculations we qualitatively show that the Ti-Al bond should be stronger than the Ti-Ti bond in γ-TiAl. Our results provide a useful reference for understanding the intrinsic bonding and mechanical properties of γ-TiAl as a high-temperature structural material.

17.
J Phys Condens Matter ; 21(49): 495402, 2009 Dec 02.
Artigo em Inglês | MEDLINE | ID: mdl-21836196

RESUMO

We perform a first-principles computational tensile test (FPCTT) on a ZnO single crystal based on density functional theory to systematically investigate structural transitions, mechanical, and intrinsic bonding properties in the three representative directions, [Formula: see text], [0001], and [Formula: see text]. Stress as a function of tensile strain shows that the ideal tensile strengths in the three directions are 16.2 GPa, 22.4 GPa, and 19.0 GPa, corresponding to strains of 0.20, 0.16, and 0.16, respectively. The [0001] is the strongest direction due to the strongest bonding between the most closely packed Zn and O(0001) layers. We demonstrate that different structures in these three directions lead to different structural transitions, i.e. from a wurtzite (WZ) to a body-centered tetragonal (BCT) structure for [Formula: see text], to a graphite-like (GP-like) structure for [0001], and to a quasi-hexagonal (quasi-HX) structure for [Formula: see text], respectively. Bond length and charge density evolution under tension indicate the occurrence of bond formation and disassociation during these structure transitions. New O-Zn bonds form in the WZ [Formula: see text] BCT and WZ [Formula: see text] quasi-HX transitions, and the original O-Zn bonds break in the WZ [Formula: see text] GP-like transition.

18.
Toxicon ; 50(8): 1126-39, 2007 Dec 15.
Artigo em Inglês | MEDLINE | ID: mdl-17854853

RESUMO

L-amino acid oxidases (LAOs) are one of the major components of snake venoms, which possess numerous biological functions. However, little is known of the influence of LAOs on organ lesions. In the present study, a unique LAO from Agkistrodon blomhoffii ussurensis snake venom named ABU-LAO was purified by Heparin-Sepharose FF chromatography followed by an ion-exchange chromatography procedure. The purified ABU-LAO appears a dimer with a molecular mass of approximately 108.8kDa. Kinetics studies showed that ABU-LAO is very active towards its substrates L-Asn, L-Phe, L-Tyr, L-Leu, L-Ile and L-Trp. The most striking observation in the present study is that ABU-LAO causes severe pneumorrhagia, pulmonary interstitial edema, fusion of pulmonary alveoli, cardiac interstitial edema and bleeding when being intravenously injected into BALB/c mice. ABU-LAO also induces liver cell necrosis and release of cytokines including IL-6, IL-12 and IL-2 from highly purified human peripheral blood monocytes and T cells, respectively. In conclusion, ABU-LAO potently induces lesions in lungs and livers. The ability of ABU-LAO will contribute to the understanding of the pathogenesis of snakebite wound.


Assuntos
Agkistrodon , Venenos de Crotalídeos/enzimologia , L-Aminoácido Oxidase/isolamento & purificação , Pulmão/efeitos dos fármacos , Animais , Citocinas/metabolismo , Eletroforese em Gel de Poliacrilamida , Cinética , L-Aminoácido Oxidase/química , L-Aminoácido Oxidase/toxicidade , L-Lactato Desidrogenase/metabolismo , Pulmão/patologia , Camundongos , Camundongos Endogâmicos BALB C , Peso Molecular , Monócitos/efeitos dos fármacos , Monócitos/imunologia , Linfócitos T/efeitos dos fármacos , Linfócitos T/imunologia
SELEÇÃO DE REFERÊNCIAS
DETALHE DA PESQUISA