RESUMEN
THz waves have been intensively applied in many fields, e.g., spectroscopy, imaging, and communications. However, owing to the rarity of available techniques for manipulating circularly polarized few-cycle THz waves on picosecond time scales, most of the current studies are conducted with linearly polarized THz waves. Here we demonstrate circularly polarized (CP) THz (dual) pulses generated by a polarization-twisting pulse/dual pulse (PTP/PTDP). The polarization-twisting optical dual pulses can be generated via a modified Michelson interferometer (MI) system, which provides the ability to control the frequency, helicity, and time interval of the dual pulses arbitrarily and individually. Such a novel, to the best of our knowledge, modulation technique shows huge potential for applications, not only in imaging and spectroscopy but also in next-generation communications.
RESUMEN
We discuss our recently reported femtosecond (fs) X-ray emission spectroscopy results on the ligand dissociation and recombination in nitrosylmyoglobin (MbNO) in the context of previous studies on ferrous haem proteins. We also present a preliminary account of femtosecond X-ray absorption studies on MbNO, pointing to the presence of more than one species formed upon photolysis.
Asunto(s)
Hemo , Ligandos , Fotólisis , Análisis Espectral , Rayos XRESUMEN
A polarization-twisting dual-pulse (PTDP) system is demonstrated using a modified Michelson interferometer (MI), in which a pellicle beam splitter is inserted into each arm. By tuning the positions of the end mirrors and pellicle beam splitters in the MI, the polarization-twisting frequency, the helicity, and the interval between two pulses can be individually manipulated. This PTDP generation system has a high degree of freedom in terms of tuning and has applications in the study of helicity dynamics in quantum matter, particularly in the terahertz (THz) regime.
RESUMEN
In haemoglobin the change from the low-spin (LS) hexacoordinated haem to the high spin (HS, S = 2) pentacoordinated domed deoxy-myoglobin (deoxyMb) form upon ligand detachment from the haem and the reverse process upon ligand binding are what ultimately drives the respiratory function. Here we probe them in the case of Myoglobin-NO (MbNO) using element- and spin-sensitive femtosecond Fe Kα and Kß X-ray emission spectroscopy at an X-ray free-electron laser (FEL). We find that the change from the LS (S = 1/2) MbNO to the HS haem occurs in ~800 fs, and that it proceeds via an intermediate (S = 1) spin state. We also show that upon NO recombination, the return to the planar MbNO ground state is an electronic relaxation from HS to LS taking place in ~30 ps. Thus, the entire ligand dissociation-recombination cycle in MbNO is a spin cross-over followed by a reverse spin cross-over process.
Asunto(s)
Hemo/química , Hemoglobinas/química , Mioglobina/química , Hemo/metabolismo , Hemoglobinas/metabolismo , Cinética , Ligandos , Modelos Moleculares , Mioglobina/metabolismo , Espectrometría por Rayos XRESUMEN
In this study, we demonstrate the switching of the direction of the photocurrent in an n-type GaAs/Al0.3Ga0.7As modulation-doped quantum well using a polarization pulse-shaping apparatus containing a 4f setup. The right- and left-polarization-twisting pulses with a polarization rotation frequency in the THz-regime are incident on a modulation-doped quantum well. The results show that the sign of the photovoltage is dependent on the direction of rotation of the polarization-twisting pulses, which can be explained by the circular photogalvanic effect combined with the production of a classical edge photocurrent from the acceleration of free electrons in the vicinity of the sample edge by the incident optical electric field. The wide range over which the polarization-rotation frequency may be tuned makes this method a powerful tool to investigate the response of an extensive variety of materials in the THz-regime.
RESUMEN
A toxin-antitoxin system, vp1842/vp1843, locates within a superintegron on the Vibrio parahaemolyticus genome chromosome I whose toxin gene vp1843 encodes a DNA nicking endonuclease. We found that the vp1843 expression in Escherichia coli cells strongly induced chromosomal DNA degradation. On the basis of these observations, we discuss a possible physiological role of vp1842/vp1843 in V. parahaemolyticus.
Asunto(s)
Cromosomas Bacterianos/genética , ADN Bacteriano/metabolismo , Escherichia coli/genética , Toxinas Biológicas/genética , Vibrio parahaemolyticus/genética , Escherichia coli/metabolismo , Expresión Génica , Toxinas Biológicas/metabolismoRESUMEN
The charge-carrier dynamics of anatase TiO2 nanoparticles in an aqueous solution were studied by femtosecond time-resolved X-ray absorption spectroscopy using an X-ray free electron laser in combination with a synchronized ultraviolet femtosecond laser (268 nm). Using an arrival time monitor for the X-ray pulses, we obtained a temporal resolution of 170 fs. The transient X-ray absorption spectra revealed an ultrafast Ti K-edge shift and a subsequent growth of a pre-edge structure. The edge shift occurred in ca. 100 fs and is ascribed to reduction of Ti by localization of generated conduction band electrons into shallow traps of self-trapped polarons or deep traps at penta-coordinate Ti sites. Growth of the pre-edge feature and reduction of the above-edge peak intensity occur with similar time constants of 300-400 fs, which we assign to the structural distortion dynamics near the surface.
RESUMEN
Type II toxins in toxin-antitoxin (TA) systems fold into a similar fold and belong to the RelE/ParE superfamily. However, they display two distinct biochemical activities: RelE toxins are mRNA interferases, while ParE toxins are DNA gyrase (Gyr) inhibitors. Previously, we found a TA system, vp1842/vp1843, on the Vibrio parahaemolyticus genome whose toxin Vp1843 belongs to the RelE/ParE toxin superfamily. Vp1843, unlike RelE toxins, has neither protein synthesis inhibitory activity nor ribonuclease activity. In this study, we examined the inhibitory potency of Vp1843 with Escherichia coli Gyr. The result showed that Vp1843, unlike other ParE toxins, had little Gyr inhibitory activity, but rather converted supercoiled DNA to open-circular DNA. Analysis showed further that Vp1843 cleaves a single strand in DNA, and that the antitoxin Vp1842 neutralized the nicking endonuclease activity of Vp1843. Mutations of Lys37 and Pro45 in Vp1843 abolished its nicking activity, suggesting that they play a crucial role in nicking endonuclease activity. To our knowledge, Vp1843 is the first toxin with DNA nicking endonuclease activity among the RelE/ParE toxin superfamily.
Asunto(s)
Toxinas Bacterianas/farmacología , Girasa de ADN/metabolismo , Inhibidores de Topoisomerasa II/farmacología , Vibrio parahaemolyticus/química , Toxinas Bacterianas/química , Toxinas Bacterianas/aislamiento & purificación , Relación Dosis-Respuesta a Droga , Escherichia coli/enzimología , Relación Estructura-Actividad , Inhibidores de Topoisomerasa II/químicaRESUMEN
We have successfully developed a circularly polarized near-field scanning optical microscope (NSOM) that enables us to irradiate circularly polarized light with spatial resolution below the diffraction limit. As a demonstration, we perform real-space mapping of the quantum Hall chiral edge states near the edge of a Hall-bar structure by injecting spin polarized electrons optically at low temperature. The obtained real-space mappings show that spin-polarized electrons are injected optically to the two-dimensional electron layer. Our general method to locally inject spins using a circularly polarized NSOM should be broadly applicable to characterize a variety of nanomaterials and nanostructures.
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Dicroismo Circular/instrumentación , Campos Magnéticos , Ensayo de Materiales/instrumentación , Microscopía de Sonda de Barrido/instrumentación , Teoría Cuántica , Radiometría/instrumentación , Diseño de Equipo , Análisis de Falla de Equipo , Reproducibilidad de los Resultados , Sensibilidad y Especificidad , Marcadores de SpinRESUMEN
Proteoglycans (PGs) are a major component of the extracellular matrix in many tissues and function as structural and regulatory molecules. PGs are composed of core proteins and glycosaminoglycan (GAG) side chains. The biosynthesis of GAGs starts with the linker region that consists of four sugar residues and is followed by repeating disaccharide units. By exome sequencing, we found that B3GALT6 encoding an enzyme involved in the biosynthesis of the GAG linker region is responsible for a severe skeletal dysplasia, spondyloepimetaphyseal dysplasia with joint laxity type 1 (SEMD-JL1). B3GALT6 loss-of-function mutations were found in individuals with SEMD-JL1 from seven families. In a subsequent candidate gene study based on the phenotypic similarity, we found that B3GALT6 is also responsible for a connective tissue disease, Ehlers-Danlos syndrome (progeroid form). Recessive loss-of-function mutations in B3GALT6 result in a spectrum of disorders affecting a broad range of skeletal and connective tissues characterized by lax skin, muscle hypotonia, joint dislocation, and spinal deformity. The pleiotropic phenotypes of the disorders indicate that B3GALT6 plays a critical role in a wide range of biological processes in various tissues, including skin, bone, cartilage, tendon, and ligament.
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Anomalías Múltiples/genética , Galactosiltransferasas/genética , Inestabilidad de la Articulación/genética , Mutación Missense , Osteocondrodisplasias/genética , Adulto , Niño , Preescolar , Femenino , Estudios de Asociación Genética , Glicosaminoglicanos/biosíntesis , Secuenciación de Nucleótidos de Alto Rendimiento , Humanos , Inestabilidad de la Articulación/enzimología , Masculino , Osteocondrodisplasias/enzimología , Análisis de Secuencia de ADNRESUMEN
We report results of a study on steric effects appearing in the scattering of an oriented CH(3)Cl molecular beam from Si(111) at surface temperatures > or = 300 K. Data presented here show that the scattered CH(3)Cl beam intensity measured at fixed scattering angles clearly depends on the initial molecular (CH(3)Cl) orientation toward the Si surface. The scattered CH(3)Cl beam intensity for the CH(3)-end collision is larger than that for the Cl-end collision, suggesting that strong anisotropy of the interaction potential induces the molecular-orientation-dependent energy dissipation during transient trapping into a shallow potential well.
Asunto(s)
Cloruro de Metilo/química , Silicio/química , Propiedades de Superficie , TemperaturaRESUMEN
SKP1-Cullin1-F-box protein (SCF) ubiquitin-ligases regulate numerous aspects of eukaryotic growth and development. Cullin-Associated and Neddylation-Dissociated (CAND1) modulates SCF function through its interactions with the CUL1 subunit. Although biochemical studies with human CAND1 suggested that CAND1 plays a negative regulatory role by sequestering CUL1 and preventing SCF complex assembly, genetic studies in Arabidopsis have shown that cand1 mutants exhibit reduced SCF activity, demonstrating that CAND1 is required for optimal SCF function in vivo. Together, these genetic and biochemical studies have suggested a model of CAND1-mediated cycles of SCF complex assembly and disassembly. Here, using the SCF(TIR1) complex of the Arabidopsis auxin response pathway, we test the SCF cycling model with Arabidopsis mutant derivatives of CAND1 and CUL1 that have opposing effects on the CAND1-CUL1 interaction. We find that the disruption of the CAND1-CUL1 interaction results in an increased abundance of assembled SCF(TIR1) complex. In contrast, stabilization of the CAND1-CUL1 interaction diminishes SCF(TIR1) complex abundance. The fact that both decreased and increased CAND1-CUL1 interactions result in reduced SCF(TIR1) activity in vivo strongly supports the hypothesis that CAND1-mediated cycling is required for optimal SCF function.
Asunto(s)
Proteínas de Arabidopsis/metabolismo , Arabidopsis/metabolismo , Proteínas Cullin/metabolismo , Proteínas Ligasas SKP Cullina F-box/metabolismo , Arabidopsis/genética , Proteínas de Arabidopsis/genética , Proteínas Cullin/genética , Análisis Mutacional de ADN , Mutación , Proteínas Ligasas SKP Cullina F-box/genética , Técnicas del Sistema de Dos HíbridosRESUMEN
The knee was assessed by normal plain radiographs in 20 achondroplasia patients (40 lower extremities), whose age ranged from 10.5 to 23 years. Five patients (seven knees) had permanent patellar dislocation. There was a significant difference between the achondroplasia group and control group (50 knees without skeletal dysplasia) for femoral sulcus angle but not for femorotibial angle, Insall-Salvati index and Q angle. Patellar dislocation for achondroplasia may be caused not only by the abnormalities of soft tissue but also a small groove of patellofemoral joint as a bony malformation.
Asunto(s)
Acondroplasia/complicaciones , Acondroplasia/diagnóstico por imagen , Rótula/diagnóstico por imagen , Luxación de la Rótula/diagnóstico por imagen , Luxación de la Rótula/etiología , Acondroplasia/fisiopatología , Adolescente , Adulto , Niño , Femenino , Humanos , Masculino , Luxación de la Rótula/fisiopatología , Radiografía , Rango del Movimiento Articular/fisiología , Estudios RetrospectivosRESUMEN
Accumulating evidence suggests the possible association between the concentrations of serum brain-derived neurotrophic factor (BDNF) and psychiatric disease with impaired brain development. Yet the reasons remain unclear. We therefore investigated the characteristics of serum BDNF as well as its age-related changes in healthy controls in comparison to autism cases. BDNF was gradually released from platelets at 4 degrees C, reached a maximal concentration after around 24 h, and remained stable until 42 h. At room temperature, BDNF was found to be immediately degraded. Circadian changes, but not seasonal changes, were found in serum levels of BDNF existing as the mature form with a molecular mass of 14 kDa. In healthy controls, the serum BDNF concentration increased over the first several years, then slightly decreased after reaching the adult level. There were no sex differences between males and females. In the autism cases, mean levels were significantly lower in children 0-9 years old compared to teenagers or adults, or to age-matched healthy controls, indicating a delayed BDNF increase with development. In a separate study of adult rats, a circadian change in serum BDNF was found to be similar to that in the cortex, indicating a possible association with cortical functions.
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Envejecimiento/sangre , Trastorno Autístico/sangre , Factor Neurotrófico Derivado del Encéfalo/sangre , Encéfalo/crecimiento & desarrollo , Encéfalo/metabolismo , Adolescente , Adulto , Distribución por Edad , Animales , Trastorno Autístico/fisiopatología , Plaquetas/metabolismo , Encéfalo/fisiopatología , Factor Neurotrófico Derivado del Encéfalo/química , Corteza Cerebral/crecimiento & desarrollo , Corteza Cerebral/metabolismo , Corteza Cerebral/fisiopatología , Niño , Preescolar , Ritmo Circadiano/fisiología , Femenino , Humanos , Lactante , Recién Nacido , Masculino , Persona de Mediana Edad , Peso Molecular , Ratas , Estaciones del Año , Distribución por Sexo , Manejo de Especímenes , Temperatura , Factores de Tiempo , Regulación hacia Arriba/fisiologíaRESUMEN
Arabidopsis (Arabidopsis thaliana) contains 15 genes encoding members of the pleiotropic drug resistance (PDR) family of ATP-binding cassette transporters. These proteins have been speculated to be involved in the detoxification of xenobiotics, however, little experimental support of this hypothesis has been obtained to date. Here we report our characterization of the Arabidopsis PDR9 gene. We isolated a semidominant, gain-of-function mutant, designated pdr9-1, that exhibits increased tolerance to the auxinic herbicide 2,4-dichlorophenoxyacetic acid (2,4-D). Reciprocally, loss-of-function mutations in PDR9 confer 2,4-D hypersensitivity. This altered auxin sensitivity defect of pdr9 mutants is specific for 2,4-D and closely related compounds as these mutants respond normally to the endogenous auxins indole-3-acetic acid and indole-butyric acid. We demonstrate that 2,4-D, but not indole-3-acetic acid transport is affected by mutations in pdr9, suggesting that the PDR9 transporter specifically effluxes 2,4-D out of plant cells without affecting endogenous auxin transport. The semidominant pdr9-1 mutation affects an extremely highly conserved domain present in all known plant PDR transporters. The single amino acid change results in increased PDR9 abundance and provides a novel approach for elucidating the function of plant PDR proteins.
Asunto(s)
Transportadoras de Casetes de Unión a ATP/genética , Proteínas de Arabidopsis/genética , Arabidopsis/genética , Resistencia a Medicamentos/genética , Ácidos Indolacéticos/metabolismo , Ácido 2,4-Diclorofenoxiacético , Transportador de Casetes de Unión a ATP, Subfamilia G , Transportadoras de Casetes de Unión a ATP/fisiología , Secuencia de Aminoácidos , Arabidopsis/fisiología , Proteínas de Arabidopsis/fisiología , Resistencia a Medicamentos/fisiología , Expresión Génica , Herbicidas/toxicidad , Datos de Secuencia Molecular , MutaciónAsunto(s)
Osteogénesis Imperfecta , Hilos Ortopédicos , Colágeno/genética , Colágeno Tipo I/genética , Cadena alfa 1 del Colágeno Tipo I , Diagnóstico Diferencial , Difosfonatos/uso terapéutico , Fijación de Fractura , Humanos , Mutación , Procedimientos Ortopédicos , Aparatos Ortopédicos , Osteogénesis Imperfecta/diagnóstico , Osteogénesis Imperfecta/etiología , Osteogénesis Imperfecta/fisiopatología , Osteogénesis Imperfecta/terapia , PronósticoRESUMEN
Selective protein degradation by the ubiquitin-proteasome pathway has emerged as a key regulatory mechanism in a wide variety of cellular processes. The selective components of this pathway are the E3 ubiquitin-ligases which act downstream of the ubiquitin-activating and -conjugating enzymes to identify specific substrates for ubiquitinylation. SCF-type ubiquitin-ligases are the most abundant class of E3 enzymes in Arabidopsis. In a genetic screen for enhancers of the tir1-1 auxin response defect, we identified eta1/axr6-3, a recessive and temperature-sensitive mutation in the CUL1 core component of the SCF(TIR1) complex. The axr6-3 mutation interferes with Skp1 binding, thus preventing SCF complex assembly. axr6-3 displays a pleiotropic phenotype with defects in numerous SCF-regulated pathways including auxin signaling, jasmonate signaling, flower development, and photomorphogenesis. We used axr6-3 as a tool for identifying pathways likely to be regulated by SCF-mediated proteolysis and propose new roles for SCF regulation of the far-red light/phyA and sugar signaling pathways. The recessive inheritance and the temperature-sensitive nature of the pleiotropically acting axr6-3 mutation opens promising possibilities for the identification and investigation of SCF-regulated pathways in Arabidopsis.