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1.
Molecules ; 24(15)2019 Jul 26.
Artigo em Inglês | MEDLINE | ID: mdl-31357420

RESUMO

For the first time, orthogonally substituted azole-carboxylate adamantane ligands were synthesized and used for preparation of coordination polymers. The angle-shaped ligands were prepared by the reaction of 1-adamantanecarboxylic acid and azoles (1H-1,2,4-triazole, 3-methyl-1H-1,2,4-triazole, 3,5-dimethyl-1H-1,2,4-triazole, 1H-tetrazole, 5-methyl-1H-tetrazole) in concentrated sulfuric acid. Variation of the solvent and substituents in azole rings allowed to prepare both 1D and 2D copper(II) and nickel(II) coordination polymers, [Cu2(trzadc)4(H2O)0.7]∙DMF∙0.3H2O, [Cu(trzadc)2(MeOH)]∙MeOH, [Ni(trzadc)2(MeOH)2] and [Cu2(mtrzadc)3(MeOH)]+NO3- (trzadc-3-(1,2,4-triazol-1-yl)-adamantane-1-carboxylic acid; mtrzadc-3-(3-methyl-1,2,4-triazol-1-yl)-adamantane-1-carboxylic acid) which were structurally characterized by single crystal X-ray diffraction. Complex [Cu(trzadc)2(MeOH)]∙MeOH was shown to act as a catalyst in the Chan-Evans-Lam arylation reaction.


Assuntos
Adamantano/análogos & derivados , Polímeros/química , Adamantano/síntese química , Adamantano/química , Adamantano/farmacologia , Catálise , Técnicas de Química Sintética , Cristalografia por Raios X , Ligantes , Estruturas Metalorgânicas , Modelos Moleculares , Conformação Molecular , Estrutura Molecular , Polímeros/síntese química , Análise Espectral
2.
Scanning ; 2018: 5489596, 2018.
Artigo em Inglês | MEDLINE | ID: mdl-30057656

RESUMO

We report on the investigation of the resistive switching (RS) in the ultrathin (≈5 nm in thickness) yttria-stabilized zirconia (YSZ) films with single layers of Au nanoparticles (NPs) by conductive atomic force microscopy (CAFM). Besides the butterfly-type hysteresis loops in the current-voltage (I-V) curves of the contact of the CAFM probe to the investigated film surface corresponding to the bipolar RS, the negative differential resistance (NDR) has been observed in the I-V curves of the AFM probe contact to the YSZ films with Au NPs in the conductive ("ON") state. The NDR has been related to the resonant tunneling of electrons through the size-quantized energy states in the ultrafine (1 to 2 nm in diameter) Au NPs built in the conductive filaments in the YSZ films.

3.
Sci Rep ; 8(1): 10764, 2018 Jul 17.
Artigo em Inglês | MEDLINE | ID: mdl-30018392

RESUMO

The short-term forecast of earthquakes associated with fault rupture is a challenge in seismology and rock mechanics. The evolution of mechanical characteristics of a local fault segment may be encoded in the ambient noise, thus, converting the ambient noise to an efficient source of information about the fault stress-strain conditions. In laboratory experiments we investigate micro-vibrations of a block-fault system induced by weak external disturbances with the purpose of getting reliable evidence of how the system transits to the metastable state. We show that precursory changes of spectral characteristics of micro-vibrations are observed for the complete spectrum of failure modes. In the course of experiments we systematically change the properties of interface to perform the transition from stick-slip to steady sliding and observe the characteristics of micro-vibrations of the laboratory block-fault system. Detected were systematical alterations of the system natural frequency and those alterations were determined by the evolution of fault stiffness. The detected regularities suggest that the final stage of seismic event preparation can be revealed in analyzing the spectral characteristics of ambient noise. The detection of natural oscillations of a block-fault system can be a new useful tool to monitor active faults in real time.

4.
Nanotechnology ; 29(30): 305603, 2018 Jul 27.
Artigo em Inglês | MEDLINE | ID: mdl-29676733

RESUMO

Semiconductor quantum dots have attracted tremendous attention owing to their novel electrical and optical properties as a result of their size dependent quantum confinement effects. This provides the advantage of tunable wavelength detection, which is essential to realize spectrally selective photodetectors. We report on the fabrication and characterization of a high performance narrow band ultraviolet photodetector (UV-B) based on Indium oxide (In2O3) nanocrystals embedded in aluminium oxide (Al2O3) matrices. The In2O3 nanocrystals are synthesized in an Al2O3 matrix by sequential implantation of In+ and [Formula: see text] ions and post-implantation annealing. The photodetector exhibits excellent optoelectronic performances with high spectral responsivity and external quantum efficiency. The spectral response shows a band-selective nature with a full width half maximum of ∼60 nm, and a responsivity reaching up to 70 A W-1 under 290 nm at 5 V bias. The corresponding rejection ratio to visible region was as high as 8400. The high performance of this photodetector makes it highly suitable for practical applications such as narrow-band spectrum-selective photodetectors. The device design based on ion-synthesized nanocrystals could provide a new approach for realizing a visible-blind photodetector.

5.
Magn Reson Chem ; 51(7): 414-23, 2013 Jul.
Artigo em Inglês | MEDLINE | ID: mdl-23695830

RESUMO

In the (1)H NMR spectra of the 1-vinylpyrroles with amino- and alkylsulfanyl groups in 5 and 2 positions, an extraordinarily large difference between resonance positions of the HA and HB terminal methylene protons of the vinyl group is discovered. Also, the one-bond (1)J(C(ß),H(B)) coupling constant is surprisingly greater than the (1)J(C(ß),H(A)) coupling constant in pyrroles under investigation, while in all known cases, there was a reverse relationship between these coupling constants. These spectral anomalies are substantiated by quantum chemical calculations. The calculations show that the amine nitrogen lone pair is removed from the conjugation with the π-system of the pyrrole ring so that it is directed toward the HB hydrogen. These factors are favorable to the emergence of the intramolecular C-HB •••N hydrogen bonding in the s-cis(N) conformation. On the other hand, the spatial proximity of the sulfur to the HB hydrogen provides an opportunity of the intramolecular C-HB •••S hydrogen bonding in the s-cis(S) conformation. Presence of the hydrogen bond critical points as well as ring critical point for corresponding chelate ring revealed by a quantum theory of atoms in molecules (QTAIM) approach confirms the existence of the weak intramolecular C-H•••N and C-H•••S hydrogen bonding. Therefore, an unusual high-frequency shift of the HB signal and the increase in the (1)J(C(ß),H(B)) coupling constant can be explained by the effects of hydrogen bonding.

6.
Magn Reson Chem ; 51(6): 339-49, 2013 Jun.
Artigo em Inglês | MEDLINE | ID: mdl-23558848

RESUMO

Comparative analysis of the (1)Н and (13)С NMR data for a series of the E and Z-1-styrylpyrroles, E and Z-1-(1-propenyl)pyrroles, 1-vinylpyrroles and styrene suggests that the conjugation between the unsaturated fragments in the former compounds is reduced. This is the result of the mutual influence of the donor p-π and π-π conjugation having opposite directions. According to the NMR data combined with the density functional theory calculations, the Z isomer of 1-styrylpyrrole has essentially a nonplanar structure because of the steric hindrance. However, the E isomer of 1-styrylpyrrole is also an out-of-plane structure despite the absence of a sterical barrier for the planar one. Deviation of the E isomer from the planar structure seems to be caused by an electronic hindrance produced by a mutual influence of the p-π and π-π conjugation. The structure of the E isomer of the 2-substituted 1-styrylpyrroles is similar to that of the 2-substituted 1-vinylpyrroles. The steric effects in the Z isomer of the 2-substituted 1-styrylpyrroles result in the large increase of the dihedral angle between planes of the pyrrole ring and double bond.


Assuntos
Pirróis/química , Teoria Quântica , Isótopos de Carbono , Elétrons , Espectroscopia de Ressonância Magnética , Estrutura Molecular , Isótopos de Nitrogênio , Prótons , Estereoisomerismo
7.
Magn Reson Chem ; 50(7): 502-10, 2012 Jul.
Artigo em Inglês | MEDLINE | ID: mdl-22615146

RESUMO

In the (13) C NMR spectra of methylglyoxal bisdimethylhydrazone, the (13) C-5 signal is shifted to higher frequencies, while the (13) C-6 signal is shifted to lower frequencies on going from the EE to ZE isomer following the trend found previously. Surprisingly, the (1) H-6 chemical shift and (1) J(C-6,H-6) coupling constant are noticeably larger in the ZE isomer than in the EE isomer, although the configuration around the -CH═N- bond does not change. This paradox can be rationalized by the C-H⋯N intramolecular hydrogen bond in the ZE isomer, which is found from the quantum-chemical calculations including Bader's quantum theory of atoms in molecules analysis. This hydrogen bond results in the increase of δ((1) H-6) and (1) J(C-6,H-6) parameters. The effect of the C-H⋯N hydrogen bond on the (1) H shielding and one-bond (13) C-(1) H coupling complicates the configurational assignment of the considered compound because of these spectral parameters. The (1) H, (13) C and (15) N chemical shifts of the 2- and 8-(CH(3) )(2) N groups attached to the -C(CH(3) )═N- and -CH═N- moieties, respectively, reveal pronounced difference. The ab initio calculations show that the 8-(CH(3) )(2) N group conjugate effectively with the π-framework, and the 2-(CH(3) )(2) N group twisted out from the plane of the backbone and loses conjugation. As a result, the degree of charge transfer from the N-2- and N-8- nitrogen lone pairs to the π-framework varies, which affects the (1) H, (13) C and (15) N shieldings.


Assuntos
Hidrazonas/química , Prótons , Aldeído Pirúvico/análogos & derivados , Isótopos de Carbono , Espectroscopia de Ressonância Magnética/normas , Estrutura Molecular , Isótopos de Nitrogênio , Aldeído Pirúvico/química , Padrões de Referência , Estereoisomerismo
8.
J Cheminform ; 3(1): 37, 2011 Oct 14.
Artigo em Inglês | MEDLINE | ID: mdl-21999342

RESUMO

BACKGROUND: The Blue Obelisk movement was established in 2005 as a response to the lack of Open Data, Open Standards and Open Source (ODOSOS) in chemistry. It aims to make it easier to carry out chemistry research by promoting interoperability between chemistry software, encouraging cooperation between Open Source developers, and developing community resources and Open Standards. RESULTS: This contribution looks back on the work carried out by the Blue Obelisk in the past 5 years and surveys progress and remaining challenges in the areas of Open Data, Open Standards, and Open Source in chemistry. CONCLUSIONS: We show that the Blue Obelisk has been very successful in bringing together researchers and developers with common interests in ODOSOS, leading to development of many useful resources freely available to the chemistry community.

9.
Magn Reson Chem ; 49(11): 740-8, 2011 Nov.
Artigo em Inglês | MEDLINE | ID: mdl-22002712

RESUMO

In the (1)H and (13)C NMR spectra of selenophene-2-carbaldehyde azine, the (1)H-5, (13)C-3 and (13)C-5 signals of the selenophene ring are shifted to higher frequencies, whereas those of the (1)H-1, (13)C-1, (13)C-2 and (13)C-4 are shifted to lower frequencies on going from the EE to ZZ isomer or from the E moiety to the Z moiety of EZ isomer. The (15)N chemical shift is significantly larger in the EE isomer relative to the ZZ isomer and in the E moiety relative to the Z moiety of EZ isomer. A very pronounced difference (60-65 mg/g) between the (77)Se resonance positions is revealed in the studied azine isomers, the (77)Se peak being shifted to higher frequencies in the ZZ isomer and in the Z moiety of EZ isomer. The trends in the changes of the measured chemical shifts are reasonably reproduced by the GIAO calculations at the MP2 level of the (1)H, (13)C, (15)N and (77)Se shielding constants in the energy-favorable conformation with the syn orientation of both selenophene rings relative to the C = N groups. The NBO analysis suggests that such an arrangement of the selenophene rings may take place because of a higher energy of some intramolecular interactions.


Assuntos
Compostos Organosselênicos/química , Teoria Quântica , Selênio/química , Isótopos , Espectroscopia de Ressonância Magnética , Conformação Molecular , Prótons , Estereoisomerismo
10.
Environ Monit Assess ; 181(1-4): 539-53, 2011 Oct.
Artigo em Inglês | MEDLINE | ID: mdl-21264683

RESUMO

The Norilsk industrial ore smelting complex (Taymyr Peninsula, Russian Federation) has significantly impacted many components of local terrestrial and aquatic environments. Whether it has had a major impact on the wider Russian Arctic remains controversial as studies are scarce. From 1986 to 2004, data on heavy metal (Cu, Ni, Zn, Hg, Cd and Hg) concentrations in fish (burbot), moss, lichens, periphyton, hydric soils and snow in and around Norilsk and the most northern parts of the Taymyr Peninsula were analysed. Very high concentrations of Cu (203 µg L⁻¹ ± 51 µg L⁻¹) and Ni (113 µg L⁻¹ ± 15 µg L⁻¹) were found in the water of the Schuchya River close to Norilsk. Heavy metal concentrations in burbot liver were highest in Lake Pyasino near Norilsk compared to other study regions that were >100 km distant. From 1989-1996, Cu (121 µg L⁻¹ ± 39 µg L⁻¹ SD), Zn (150 µg L⁻¹) ± 70 µg L⁻¹) and Ni (149 µg L⁻¹ ± 72 µg L⁻¹) snow concentrations were greatest in Norilsk, but were low elsewhere. By 2004, these concentrations had dropped significantly, especially for Cu-74 µg L⁻¹ (±18.7 µg L⁻¹ SD), Zn-81.7 µg L⁻¹ (± 31.3 µg L⁻¹ SD) and Ni-80 µg L⁻¹(±18.0 µg L⁻¹ SD). Norilsk and its surroundings are subject to heavy pollution from the Norilsk metallurgical industry but these are absent from the greater Arctic region due to the prevailing winds and the Byrranga Mountains. Pollution abatement measures have been made so further investigations are necessary in order to assess their efficiency.


Assuntos
Monitoramento Ambiental , Metais Pesados/análise , Poluentes do Solo/análise , Enxofre/análise , Poluentes Químicos da Água/análise , Ecossistema , Poluição Ambiental/estatística & dados numéricos , Água Doce/química , Indústrias , Federação Russa , Neve/química , Solo/química , Sphagnopsida/química
11.
Magn Reson Chem ; 48(9): 685-92, 2010 Sep.
Artigo em Inglês | MEDLINE | ID: mdl-20623827

RESUMO

The (1)H, (13)C and (15)N NMR studies have shown that the E and Z isomers of pyrrole-2-carbaldehyde oxime adopt preferable conformation with the syn orientation of the oxime group with respect to the pyrrole ring. The syn conformation of E and Z isomers of pyrrole-2-carbaldehyde oxime is stabilized by the N-H...N and N-H...O intramolecular hydrogen bonds, respectively. The N-H...N hydrogen bond in the E isomer causes the high-frequency shift of the bridge proton signal by about 1 ppm and increase the (1)J(N, H) coupling by approximately 3 Hz. The bridge proton shows further deshielding and higher increase of the (1)J(N, H) coupling constant due to the strengthening of the N-H...O hydrogen bond in the Z isomer. The MP2 calculations indicate that the syn conformation of E and Z isomers is by approximately 3.5 kcal/mol energetically less favorable than the anti conformation. The calculations of (1)H shielding and (1)J(N, H) coupling in the syn and anti conformations allow the contribution to these constants from the N-H...N and N-H...O hydrogen bondings to be estimated. The NBO analysis suggests that the N-H...N hydrogen bond in the E isomer is a pure electrostatic interaction while the charge transfer from the oxygen lone pair to the antibonding orbital of the N-H bond through the N-H...O hydrogen bond occurs in the Z isomer.


Assuntos
Simulação de Dinâmica Molecular , Oximas/química , Pirróis/química , Teoria Quântica , Isótopos de Carbono , Ligação de Hidrogênio , Espectroscopia de Ressonância Magnética , Conformação Molecular , Isótopos de Nitrogênio , Prótons , Padrões de Referência , Estereoisomerismo
12.
Biochemistry ; 49(18): 3919-27, 2010 May 11.
Artigo em Inglês | MEDLINE | ID: mdl-20361759

RESUMO

The antiparallel dimer (APD) is a unique actin species, which can be detected in the early stages of actin polymerization. In this work, we introduce novel tools for examination of the effects of the APD on actin polymerization. We document that bifunctional methanothiosulfonate (MTS) reagents are an attractive alternative to the routinely used p-phenylene maleimide (pPDM) for APD detection, allowing for fast and efficient cross-linking under conditions of actin polymerization at neutral pH. We report also that pyrene-labeled yeast actin mutant A167C/C374A (C167PM) forms significant amounts of stable APD in solution, without chemical cross-linking or polymerization-affecting compounds, and that the kinetics of APD transformation and decay upon actin polymerization can be easily monitored. The dimerization of C167PM has been characterized in sedimentation equilibrium experiments (K(d) approximately 0.3 microM). This new system offers the advantage of assessing the effects of the APD under physiological conditions (pH, ionic strength, and Mg(2+) concentration) and testing for conformational transitions in the APD during nucleation-polymerization reactions or/and in the presence of actin-interacting factors. The results obtained using two different systems (C167PM actin and polylysine-induced polymerization of alpha-actin) show that the APD decays at a rate slower than that at which the filaments elongate, revealing its transient incorporation into filaments, and confirm that it inhibits the nucleation and elongation of actin filaments.


Assuntos
Actinas/química , Leveduras/química , Citoesqueleto de Actina/química , Citoesqueleto de Actina/genética , Citoesqueleto de Actina/metabolismo , Actinas/genética , Actinas/metabolismo , Dimerização , Cinética , Ligação Proteica , Leveduras/genética , Leveduras/metabolismo
13.
Magn Reson Chem ; 47(10): 879-84, 2009 Oct.
Artigo em Inglês | MEDLINE | ID: mdl-19582802

RESUMO

In the (1)H and (13)C NMR spectra of 1-(2-selenophenyl)-1-alkanone oximes, the (1)H, the (13)C-3 and (13)C-5 signals of the selenophene ring are shifted by 0.1-0.4, 2.5-3.0 and 5.5-6.0 ppm, respectively, to higher frequencies, whereas those of the (13)C-1, (13)C-2 and (13)C-4 carbons are shifted by 4-5, approximately 11 and approximately 1.7 ppm to lower frequencies on going from the E to Z isomer. The (15)N chemical shift of the oximic nitrogen is larger by 13-16 ppm in the E isomer relative to the Z isomer. An extraordinarily large difference (above 90 ppm) between the (77)Se resonance positions is revealed in the studied oxime isomers, the (77)Se peak being shifted to higher frequencies in the Z isomer. The trends in the changes of the measured chemical shifts are well reproduced by the GIAO calculations of the (1)H, (13)C, (15)N and (77)Se shielding constants in the energy-favorable conformation with the syn orientation of the-C=N-O-H group relative to the selenophene ring.


Assuntos
Espectroscopia de Ressonância Magnética/normas , Compostos Organosselênicos/química , Oximas/química , Prótons , Selênio/química , Isótopos de Carbono , Espectroscopia de Ressonância Magnética/métodos , Estrutura Molecular , Isótopos de Nitrogênio , Padrões de Referência , Estereoisomerismo
14.
Magn Reson Chem ; 47(7): 601-4, 2009 Jul.
Artigo em Inglês | MEDLINE | ID: mdl-19437455

RESUMO

In the acetylenic aldehyde oximes with substituents containing silicon and germanium, the (13)C NMR signal of the C-2 carbon of triple bond is shifted by 3.5 ppm to lower frequency and that of the C-3 carbon is moved by 7 ppm to higher frequency on going from E to Z isomer. A greater low-frequency effect of 5.5 ppm on the C-2 carbon signal and a greater high-frequency effect of 11 ppm on the C-3 carbon signal are observed in the analogous acetylenic ketone oximes. The carbon chemical shift of the C=N bond is larger by 4 ppm in E isomer relative to Z isomer for the aldehyde and ketone oximes. The (29)Si chemical shifts in the silicon containing acetylenic aldehyde and ketone oximes are almost the same for the diverse isomers. The trends in changes of the measured chemical shifts are well reproduced by the gauge-including atomic orbital (GIAO) calculations of the (13)C and (29)Si shielding constants.

15.
J Mol Biol ; 365(5): 1350-8, 2007 Feb 02.
Artigo em Inglês | MEDLINE | ID: mdl-17134718

RESUMO

Cofilin is essential for cell viability and for actin-based motility. Cofilin severs actin filaments, which enhances the dynamics of filament assembly. We investigated the mechanism of filament severing by cofilin with direct fluorescence microscopy observation of single actin filaments in real time. In cells, actin filaments are likely to be attached at multiple points along their length, and we found that attaching filaments in such a manner greatly increased the efficiency of filament severing by cofilin. Cofilin severing increased and then decreased with increasing concentration of cofilin. Together, these results indicate that cofilin severs the actin filament by a mechanism of allosteric and cooperative destabilization. Severing is more efficient when relaxation of this cofilin-induced instability of the actin filament is inhibited by restricting the flexibility of the filament. These conclusions have particular relevance to cofilin function during actin-based motility in cells and in synthetic systems.


Assuntos
Citoesqueleto de Actina/metabolismo , Cofilina 1/metabolismo , Citoesqueleto de Actina/efeitos dos fármacos , Actinas/metabolismo , Animais , Caenorhabditis elegans/metabolismo , Gelsolina/metabolismo , Camundongos , Subfragmentos de Miosina/metabolismo , Rodaminas/farmacologia , Saccharomyces cerevisiae/metabolismo
16.
Biophys J ; 91(12): 4490-9, 2006 Dec 15.
Artigo em Inglês | MEDLINE | ID: mdl-16997870

RESUMO

Cofilin/ADF, beryllium fluoride complex (BeFx), and phalloidin have opposing effects on actin filament structure and dynamics. Cofilin/ADF decreases the stability of F-actin by enhancing disorder in subdomain 2, and by severing and accelerating the depolymerization of the filament. BeFx and phalloidin stabilize the subdomain 2 structure and decrease the critical concentration of actin, slowing the dissociation of monomers. Yeast cofilin, unlike some other members of the cofilin/ADF family, binds to F-actin in the presence of BeFx; however, the rate of its binding is strongly inhibited by BeFx and decreases with increasing pH. The inhibition of the cofilin binding rate increases with the time of BeFx incubation with F-actin, indicating the existence of two BeFx-F-actin complexes. Cofilin dissociates BeFx from the filament, while BeFx does not bind to F-actin saturated with cofilin, presumably because of the cofilin-induced changes in the nucleotide-binding cleft of F-actin. These changes are apparent from the increase in the fluorescence intensity of F-actin bound epsilon-ADP upon cofilin binding and a decrease in its accessibility to collisional quenchers. BeFx also affects the nucleotide-binding cleft of F-actin, as indicated by an increase in the fluorescence intensity of epsilon-ADP-F-actin. Phalloidin and cofilin inhibit, but do not exclude each other binding to their complexes with F-actin. Phalloidin promotes the dissociation of cofilin from F-actin and slowly reverses the cofilin-induced disorder in the DNase I binding loop of subdomain 2.


Assuntos
Fatores de Despolimerização de Actina/química , Actinas/química , Difosfato de Adenosina/química , Berílio/química , Fluoretos/química , Faloidina/química , Citoesqueleto de Actina/química , Actinas/antagonistas & inibidores , Animais , Sítios de Ligação , Proteínas Fúngicas/antagonistas & inibidores , Proteínas Fúngicas/química , Estrutura Terciária de Proteína , Coelhos
17.
Cell Motil Cytoskeleton ; 63(9): 533-42, 2006 Sep.
Artigo em Inglês | MEDLINE | ID: mdl-16847879

RESUMO

Cofilin plays an important role in actin turnover in cells by severing actin filaments and accelerating their depolymerization. The role of pH in the severing by cofilin was examined using fluorescence microscopy. To facilitate the imaging of actin filaments and to avoid the use of rhodamine phalloidin, which competes with cofilin, alpha-actin was labeled with tetramethylrhodamine cadaverine (TRC) at Gln41. The TRC-labeling inhibited actin treadmilling strongly, as measured by epsilonATP release. Cofilin binding, detected via an increase in light scattering, and the subsequent conformational change in filament structure, as detected by TRC fluorescence decay, occurred 2-3 times faster at pH 6.8 than at pH 8.0. In contrast, actin filaments severing by cofilin was pH-independent. The pH-independent severing by cofilin was confirmed using actin labeled at Cys374 with Oregon Green 488 maleimide. The depolymerization of actin by cofilin was faster at high pH.


Assuntos
Fatores de Despolimerização de Actina/metabolismo , Actinas/metabolismo , Saccharomyces cerevisiae/metabolismo , Citoesqueleto de Actina/metabolismo , Animais , Ácidos Carboxílicos/química , Etenoadenosina Trifosfato/metabolismo , Concentração de Íons de Hidrogênio , Camundongos , Ligação Proteica , Coelhos , Rodaminas/química , Saccharomyces cerevisiae/citologia , Fatores de Tempo
18.
FEBS J ; 273(7): 1488-96, 2006 Apr.
Artigo em Inglês | MEDLINE | ID: mdl-16689934

RESUMO

Inorganic phosphate (Pi) and cofilin/actin depolymerizing factor proteins have opposite effects on actin filament structure and dynamics. Pi stabilizes the subdomain 2 in F-actin and decreases the critical concentration for actin polymerization. Conversely, cofilin enhances disorder in subdomain 2, increases the critical concentration, and accelerates actin treadmilling. Here, we report that Pi inhibits the rate, but not the extent of cofilin binding to actin filaments. This inhibition is also significant at physiological concentrations of Pi, and more pronounced at low pH. Cofilin prevents conformational changes in F-actin induced by Pi, even at high Pi concentrations, probably because allosteric changes in the nucleotide cleft decrease the affinity of Pi to F-actin. Cofilin induced allosteric changes in the nucleotide cleft of F-actin are also indicated by an increase in fluorescence emission and a decrease in the accessibility of etheno-ADP to collisional quenchers. These changes transform the nucleotide cleft of F-actin to G-actin-like. Pi regulation of cofilin binding and the cofilin regulation of Pi binding to F-actin can be important aspects of actin based cell motility.


Assuntos
Fatores de Despolimerização de Actina/metabolismo , Actinas/metabolismo , Fosfatos/metabolismo , Actinas/química , Sítios de Ligação , Ligação Proteica , Estrutura Terciária de Proteína , Subtilisina/metabolismo
19.
J Mol Biol ; 356(2): 325-34, 2006 Feb 17.
Artigo em Inglês | MEDLINE | ID: mdl-16375920

RESUMO

Using site-specific fluorescence probes and cross-linking we demonstrated that cofilin (ADF), a key regulator of actin cellular dynamics, weakens longitudinal contacts in F-actin in a cooperative manner. Differential scanning calorimetry detected a dual nature of cofilin effects on F-actin conformation. At sub-stoichiometric cofilin to actin ratios, cofilin stabilized sterically and non-cooperatively protomers at the points of attachment, and destabilized allosterically and cooperatively protomers in the cofilin-free parts of F-actin. This destabilizing effect had a long range, with one cofilin molecule affecting more than 100 protomers, and concentration-dependent amplitude that reached maximum at about 1:2 molar ratio of cofilin to actin. In contrast to existing models, our results suggest an allosteric mechanism of actin depolymerization by cofilin. We propose that cofilin is less likely to sever actin filaments at the points of attachment as thought previously. Instead, due to its dual structural effect, spontaneous fragmentation occurs most likely in cofilin-free segments of filaments weakened allosterically by nearby cofilin molecules.


Assuntos
Fatores de Despolimerização de Actina/química , Actinas/química , Conformação Proteica , Fatores de Despolimerização de Actina/metabolismo , Actinas/metabolismo , Regulação Alostérica , Animais , Varredura Diferencial de Calorimetria , Dissulfetos/química , Modelos Moleculares , Coelhos
20.
J Biol Chem ; 278(8): 5517-22, 2003 Feb 21.
Artigo em Inglês | MEDLINE | ID: mdl-12468534

RESUMO

Vertebrate striated muscle contraction is regulated in a Ca(2+)-dependent fashion by tropomyosin (Tm) and troponin (Tn). This regulation involves shifts in the position of Tm and Tn on actin filaments and may include conformational changes in actin that are then communicated to myosin subfragment 1 (S1). To determine whether subdomain 2 of actin plays a role in this regulation, the DNase-I loop 38-52 of this subdomain was cleaved by subtilisin between residues Met(47) and Gly(48). Despite impaired unregulated function, the potentiation and regulation of cleaved actin movement in the in vitro motility assay was not significantly different from that of uncleaved actin. Stopped-flow measurements of ADP release from regulated and unregulated cleaved acto-S1 showed a marked increase in ADP release from acto-S1 in the presence of the regulatory complex. The enhancement of the actin affinity for S1 in the presence of regulatory proteins was greater for uncleaved than for cleaved F-actin. Finally, both cleaved and uncleaved actins protect myosin loop 1 from papain cleavage equally well. Our results suggest that the potentiation of actin function in the in vitro motility assay by regulatory proteins stems from changes in cross-bridge cycle kinetics. In addition, the unimpaired calcium-sensitive regulation of cleaved actin indicates that subdomain 2 conformation does not play an essential role in the regulation process.


Assuntos
Actinas/química , Actinas/metabolismo , Subfragmentos de Miosina/metabolismo , Subtilisina/metabolismo , Tropomiosina/metabolismo , Troponina/metabolismo , Actomiosina/metabolismo , Animais , Sítios de Ligação , Desoxirribonuclease I , Cinética , Contração Muscular/fisiologia , Músculo Esquelético/fisiologia , Subfragmentos de Miosina/química , Papaína/metabolismo , Fragmentos de Peptídeos/metabolismo , Hormônios Hipofisários/metabolismo , Coelhos
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