RESUMEN
The light absorption coefficient of hydrogenated nanocrystalline silicon has been engineered to have a Gaussian distribution by means of absorption modification using a femtosecond laser. The absorption-modified sample exhibits a significant absorption enhancement of up to â¼700%, and the strong absorption does not depend on the incident light. We propose a model responsible for this interesting behavior. In addition, we present an optical limiter constructed through this absorption engineering method.
RESUMEN
Nonlinear absorption (NLA) of hydrogenated nanocrystalline silicon (nc-Si:H) has been investigated through the open aperture Z-scan method for the photon energy of the incident irradiance slightly less than the bandgap of the sample. NLA responses have been observed to be highly sensitive to the wavelength and intensity of the incident irradiance as well as to the bandgap of the sample, indicating greatly tunable NLA of nc-Si:H. The band tail of nc-Si:H appears to play a crucial role in such NLA responses.
RESUMEN
We have carried out detailed investigations on the light absorption mechanism in single crystalline silicon (c-Si) (core)/amorphous Si (a-Si) (shell) coaxial nanowires (NWs). Based on the Lorenz-Mie light scattering theory, we have found that the light absorption in the coaxial NWs relies on the leaky mode resonances and that the light absorption can be optimized towards photovoltaic applications when the a-Si shell thickness is about twice the c-Si core radius. The photocurrent has been found to be enhanced up to â¼ 560% compared to c-Si NWs, and to be further enhanced up to â¼ 60% by coating the nonabsorbing dielectric shells.
RESUMEN
We have successfully fabricated well-ordered silicon nanowire (SiNW) arrays of smooth surface by using a low-cost and facile Ag-assisted chemical etching technique. We have experimentally found that the reflectance can be significantly suppressed (<1%) over a wide solar spectrum (300-1000 nm) in the as-grown samples. Also, based on our bundled model, we have used rigorous coupled-wave analysis to simulate the reflectance in SiNW arrays, and found that the calculated results are in good agreement with the experimental data. From a further simulation study on the light absorption in SiNW arrays, we have obtained a photocurrent enhancement of up to 425% per unit volume of material as compared to crystalline Si, implying that effective light trapping can be realized in the as-grown samples. In addition, we have demonstrated experimentally and theoretically that the as-grown samples have an omnidirectional high-efficiency antireflection property.
RESUMEN
LB50016 was characterized as a selective and potent 5-HT1A receptor agonist and evaluate its anxiolytic and antidepressant activities. It shows high affinity for 5-HT1A receptor, moderate affinity for alpha 2 adrenergic and 5-HT2A receptors and no significant affinity for other receptors tested. Hypothermia and increased serum corticosterone level were observed in LB50016-treated rats, which are mediated mostly by post synaptic 5-HT1A receptor activation. In the mouse forced swim model for depression, LB50016-elicited dose-dependent reductions in immobility time, showing ED50 of approximately 3 mg/kg i.p., which was blocked by pretreatment of NAN-190, 5-HT1A antagonist. In face-to-face test for anxiolytic activity in mice, estimated ED50 was 2 mg/kg, i.p. In isolation-induced aggression test with mice, fifty-fold increases in latency to attack were observed at 30 min and last up to 4 h after LB50016 treatment (3 mg/kg, i.p.). Taken together, LB50016-induced pharmacological activities are mediated by activation of 5-HT1A receptors, offering an effective therapeutic candidate in the management of anxiety and depression in humans.
Asunto(s)
Óxidos S-Cíclicos/farmacología , Receptores de Serotonina/efectos de los fármacos , Agonistas de Receptores de Serotonina/farmacología , Tiazoles/farmacología , 8-Hidroxi-2-(di-n-propilamino)tetralin/metabolismo , Agresión/efectos de los fármacos , Animales , Ansiolíticos/farmacología , Antidepresivos/farmacología , Temperatura Corporal/efectos de los fármacos , Corticosterona/sangre , Masculino , Ratas , Ratas Sprague-Dawley , Receptores de Serotonina 5-HT1RESUMEN
The fdsGBACD operon encoding the four subunits of the NAD+-reducing formate dehydrogenase of Ralstonia eutropha H16 was cloned and sequenced. Sequence comparisons indicated a high resemblance of FdsA (alpha-subunit) to the catalytic subunits of formate dehydrogenases containing a molybdenum (or tungsten) cofactor. The NH2-terminal region (residues 1-240) of FdsA, lacking in formate dehydrogenases not linked to NAD(P)+, exhibited considerable similarity to that of NuoG of the NADH:ubiquinone oxidoreductase from Escherichia coli as well as to HoxU and the NH2-terminal segment of HndD of NAD(P)+-reducing hydrogenases. FdsB (beta-subunit) and FdsG (gamma-subunit) are closely related to NuoF and NuoE, respectively, as well as to HoxF and HndA. It is proposed that the NH2-terminal domain of FdsA together with FdsB and FdsG constitute a functional entity corresponding to the NADH dehydrogenase (diaphorase) part of NADH:ubiquinone oxidoreductase and the hydrogenases. No significant similarity to any known protein was observed for FdsD (delta-subunit). The predicted product of fdsC showed the highest resemblance to FdhD from E. coli, a protein required for the formation of active formate dehydrogenases in this organism. Transcription of the fds operon is subject to formate induction. A promoter structure resembling the consensus sequence of sigma70-dependent promoters from E. coli was identified upstream of the transcriptional start site determined by primer extension analysis.
Asunto(s)
Cupriavidus necator/enzimología , Formiato Deshidrogenasas/genética , NAD/metabolismo , Operón , Secuencia de Aminoácidos , Secuencia de Bases , Clonación Molecular , Cartilla de ADN , Electrones , Formiato Deshidrogenasas/química , Formiato Deshidrogenasas/metabolismo , Regulación Bacteriana de la Expresión Génica , Regulación Enzimológica de la Expresión Génica , Datos de Secuencia Molecular , Regiones Promotoras Genéticas , Conformación Proteica , Homología de Secuencia de AminoácidoRESUMEN
Cantilever magnetometry has been used to measure the upper critical magnetic field H(c2) of the quasi-one-dimensional molecular organic superconductor (TMTSF)2ClO4. From simultaneous resistivity and torque magnetization experiments conducted under precise field alignment, H(c2) at low temperature is shown to reach 5 T, nearly twice the Pauli paramagnetic limit imposed on spin singlet superconductors. These results constitute the first thermodynamic evidence for a large H(c2) in this system and provide support for spin triplet pairing in this unconventional superconductor.
RESUMEN
Here we show that the extent of electron flow through the cbb(3) oxidase of Rhodobacter sphaeroides is inversely related to the expression levels of those photosynthesis genes that are under control of the PrrBA two-component activation system: the greater the electron flow, the stronger the inhibitory signal generated by the cbb(3) oxidase to repress photosynthesis gene expression. Using site-directed mutagenesis, we show that intramolecular electron transfer within the cbb(3) oxidase is involved in signal generation and transduction and this signal does not directly involve the intervention of molecular oxygen. In addition to the cbb(3) oxidase, the redox state of the quinone pool controls the transcription rate of the puc operon via the AppA-PpsR antirepressor-repressor system. Together, these interacting regulatory circuits are depicted in a model that permits us to understand the regulation by oxygen and light of photosynthesis gene expression in R.SPHAEROIDES:
Asunto(s)
Proteínas Bacterianas , Complejo IV de Transporte de Electrones/química , Electrones , Regulación Enzimológica de la Expresión Génica , Oxidación-Reducción , Rhodobacter sphaeroides/química , Antifúngicos/farmacología , Western Blotting , Carbonil Cianuro m-Clorofenil Hidrazona/farmacología , Proteínas de Unión al ADN/química , Relación Dosis-Respuesta a Droga , Electroforesis en Gel de Poliacrilamida , Ionóforos/farmacología , Luz , Metacrilatos , Modelos Biológicos , Mutagénesis Sitio-Dirigida , Operón , Oxígeno/metabolismo , Fotosíntesis/genética , Proteínas Represoras/química , Transducción de Señal , Espectrofotometría , Tiazoles/farmacología , Factores de Tiempo , Transcripción Genética , Rayos Ultravioleta , Desacopladores/farmacologíaRESUMEN
The volume of electron flow through the cbb3 branch of the electron transport chain and the redox state of the quinone pool generate signals that regulate photosynthesis gene expression in Rhodobacter sphaeroides. An inhibitory signal is generated at the level of the catalytic subunit of the cbb3 cytochrome c oxidase and is transduced through the membrane-localized PrrC polypeptide to the PrrBA two-component activation system, which controls the expression of most of the photosynthesis genes in response to O2. The redox state of the quinone pool is monitored by the redox-active AppA antirepressor protein, which determines the functional state of the PpsR repressor protein. The antirepressor/repressor system as well as a modulator of AppA function, TspO, together with FnrL and PrrA stringently control photopigment gene expression. These regulatory elements, together with spectral complex-specific assembly factors, control the ultimate cellular levels and composition of the photosynthetic membrane.
Asunto(s)
Proteínas Bacterianas/metabolismo , Regulación Bacteriana de la Expresión Génica , Fotosíntesis/genética , Proteínas del Complejo del Centro de Reacción Fotosintética/metabolismo , Rhodobacter sphaeroides/fisiología , Proteínas Bacterianas/genética , Oxidación-Reducción , Proteínas del Complejo del Centro de Reacción Fotosintética/genética , Rhodobacter sphaeroides/genéticaRESUMEN
The transcriptional regulator gene fdsR was identified 150 bp upstream of the divergently oriented fdsGBACD operon encoding the soluble, NAD+-linked formate dehydrogenase in the chemoautotrophic bacterium Ralstonia eutropha H16. Its deduced product, FdsR, displays a basal sequence similarity to the regulatory proteins of the LysR family. The carboxy-terminal domain of FdsR contains a short region that is conserved in formate dehydrogenases. Deletion of fdsR revealed a dual regulatory effect of FdsR on the fds operon by acting as transcriptional activator in the presence of formate or as repressor in the absence of formate. Studies with fdsR transcriptional fusions also suggested a negative autoregulation of the gene. A promoter structure resembling sigma70-dependent promoters from Escherichia coli was identified upstream of the fdsR transcriptional start site. FdsR purified to homogeneity after overexpression of fdsR in E. coli is a 130 kDa homotetramer binding to the fds control region located between the fdsR and fdsG genes. Formate significantly increased the binding affinity of FdsR for this region. Two FdsR binding sites characterized by the inverted-repeat structure ATANG-N10-CNTAT were identified. The regulatory pattern found in R. eutropha was also observed in the heterologous host E. coli and results from a novel mode of control of formate dehydrogenase genes.
Asunto(s)
Proteínas Bacterianas , Cupriavidus necator/genética , Formiato Deshidrogenasas/genética , Regulación Bacteriana de la Expresión Génica , Genes Reguladores , Operón , Proteínas Represoras/genética , Transactivadores/genética , Secuencia de Aminoácidos , Secuencia de Bases , Cupriavidus necator/enzimología , Formiato Deshidrogenasas/metabolismo , Datos de Secuencia Molecular , NAD/metabolismo , Plásmidos/genética , Proteínas Represoras/química , Proteínas Represoras/metabolismo , Análisis de Secuencia de ADN , Transactivadores/química , Transactivadores/metabolismo , Transcripción GenéticaRESUMEN
We have previously shown that the flow of reductant through the cbb3 terminal cytochrome c oxidase of Rhodobacter sphaeroides is essential to the repression of photosynthesis (PS) gene expression in the presence of oxygen by inhibiting the functional activity of the Prr two-component activation system. To gain further insight into the role of the cbb3 oxidase and the cognate ccoNOQP operon in the oxygen regulation of PS gene expression, we constructed nonpolar, in-frame deletions within the ccoN and ccoQ genes. Whereas mutations in ccoN, ccoQ, and ccoP resulted in PS gene expression in the presence of oxygen, only the ccoQ mutation showed both the normal flow of reductant through the cbb3 oxidase and the absence of any alteration in the relative levels of spheroidene and spheroidenone, as is observed for those mutations in the cco operon that result in the loss of terminal oxidase activity. Consistent with these findings is the observation that extra copies of the ccoNOQP operon in trans resulted in the decreased formation of both the B800-850 and B875 spectral complexes under anaerobic growth conditions. These results in conjunction with our earlier findings indicate that (1) the flow of reductant through the cbb3 terminal oxidase is a prerequisite to the regulation of PS gene expression by the Prr two-component regulatory system, (2) the CcoQ protein is involved in conveying the signal derived from reductant flow through the cbb3 terminal oxidase to the Prr regulatory pathway, (3) there is reductant flow through this terminal oxidase under anaerobic conditions, and as a result, the activity of the Prr system is still subject to cbb3 regulation, and (4) the acceptor for reductant flow through cbb3 under anaerobic conditions is in whole or in part involved in the conversion of spheroidene to spheroidenone.
Asunto(s)
Complejo IV de Transporte de Electrones/química , Proteínas Hierro-Azufre , Oxidorreductasas/química , Rhodobacter sphaeroides/enzimología , Carotenoides/química , Complejo IV de Transporte de Electrones/genética , Complejo IV de Transporte de Electrones/metabolismo , Activación Enzimática/genética , Dosificación de Gen , Regulación Bacteriana de la Expresión Génica , Genes Reporteros , Prueba de Complementación Genética , Vectores Genéticos/síntesis química , Sustancias Macromoleculares , Mutagénesis Sitio-Dirigida , Oxidación-Reducción , Oxidorreductasas/genética , Oxidorreductasas/metabolismo , Fotosíntesis/genética , Rhodobacter sphaeroides/genética , Eliminación de Secuencia , Espectrofotometría , Relación Estructura-ActividadRESUMEN
The PrrBA two-component activation system of Rhodobacter sphaeroides plays a major role in the induction of photosynthesis gene expression under oxygen-limiting or anaerobic conditions. The PrrB histidine kinase is composed of two structurally identifiable regions, the conserved C-terminal kinase/phosphatase domain and the N-terminal membrane-spanning domain with six transmembrane helices framing three periplasmic and two cytoplasmic loops. Using a set of PrrB mutants with lesions in the transmembrane domain, we demonstrate that the central portion of the PrrB transmembrane domain including the second periplasmic loop plays an important role in both sensing and signal transduction. Signal transduction via the transmembrane domain is ultimately manifested by controlling the activity of the C-terminal kinase/phosphatase domain. The extent of signal transduction is determined by the ability of the transmembrane domain to sense the strength of the inhibitory signal received from the cbb(3) terminal oxidase (J.-I Oh, and S. Kaplan, EMBO J. 19:4237-4247, 2000). Therefore, the intrinsic ("default") state of PrrB is in the kinase-dominant mode. It is also demonstrated that the extent of prrB gene expression is subject to the negative autoregulation of the PrrBA system.
Asunto(s)
Proteínas Quinasas/fisiología , Rhodobacter sphaeroides/enzimología , Transducción de Señal , Secuencia de Aminoácidos , Regulación Bacteriana de la Expresión Génica , Histidina Quinasa , Proteínas de la Membrana/fisiología , Datos de Secuencia Molecular , Operón , Fotosíntesis/genética , Proteínas Quinasas/genética , Rhodobacter sphaeroides/genéticaRESUMEN
FnrL, the homolog of the global anaerobic regulator Fnr, is required for the induction of the photosynthetic apparatus in Rhodobacter sphaeroides 2.4.1. Thus, the precise role of FnrL in photosynthesis (PS) gene expression and its interaction(s) with other regulators of PS gene expression are of considerable importance to our understanding of the regulatory circuitry governing spectral complex formation. Using a CcoP and FnrL double mutant strain, we obtained results which suggested that FnrL is not involved in the transduction of the inhibitory signal, by which PS gene expression is "silenced," emanating from the cbb(3) oxidase encoded by the ccoNOQP operon under aerobic conditions. The dominant effect of the ccoP mutation in the FnrL mutant strain with respect to spectral complex formation under aerobic conditions and restoration of a PS-positive phenotype suggested that inactivation of the cbb(3) oxidase to some extent bypasses the requirement for FnrL in the formation of spectral complexes. Additional analyses revealed that anaerobic induction of the bchE, hemN, and hemZ genes, which are involved in the tetrapyrrole biosynthetic pathways, requires FnrL. Thus, FnrL appears to be involved at multiple loci involved in the regulation of PS gene expression. Additionally, bchE was also shown to be regulated by the PrrBA two-component system, in conjunction with hemN and hemZ. These and other results to be discussed permit us to more accurately describe the role of FnrL as well as the interactions between the FnrL, PrrBA, and other regulatory circuits in the regulation of PS gene expression.
Asunto(s)
Coproporfirinógeno Oxidasa , Fotosíntesis/genética , Rhodobacter sphaeroides/genética , Transactivadores , Aerobiosis , Proteínas Bacterianas/genética , Bacterioclorofilas/biosíntesis , Regulación Bacteriana de la Expresión Génica , Genes Bacterianos , Hemo/biosíntesis , Oxidorreductasas/genética , Protoclorofilida/análogos & derivados , Protoclorofilida/metabolismo , Protoporfirinas/metabolismo , Pirroles/metabolismo , Transducción de Señal , TetrapirrolesRESUMEN
During in vitro incubation for several hours human circulating blood leucocytes developed procoagulant activity (PCA) which was identified as tissue thromboplastin-like activity and which remained specifically associated with monocytes. Adherence of monocytes to glass stimulated these cells to generate PCA. When cuprophane was used, both the degree of adherence of monocytes and PCA generation by these cells was significantly less. In addition, when the monocytes were incubated upon a monolayer of cultured endothelial cells only minor PCA generation was detectable. After incubation on glass the non-adherent monocytes had negligible PCA in comparison to the adherent monocytes. Protein synthesis inhibitors (cycloheximide and actinomycin D) inhibited PCA generation but did not affect monocyte adherence. These results demonstrate that adherence of monocytes is a stimulus for the generation of PCA.
Asunto(s)
Coagulación Sanguínea , Monocitos/fisiología , Proteínas Sanguíneas/biosíntesis , Adhesión Celular , Cicloheximida/farmacología , Dactinomicina/farmacología , Endotelio/citología , Vidrio , Humanos , Técnicas In Vitro , Monocitos/efectos de los fármacosRESUMEN
Immune reactions are often associated with fibrin deposition. The mechanisms that lead to this fibrin formation have not yet been clarified. In this study, we show that mononuclear leukocytes (MNL) from donors with a high proliferative response to protein derivative of tuberculin (PPD) have on average 2.5 to 15-fold more thromboplastin (TP) activity, both exposed and intracellularly, compared with MNL from low responder after 4, 7 and 11 days of culture in the presence of PPD. This difference was not observed between the two groups of donors when PPD was omitted from the culture medium. Further evidence for a specific enhancement of the leukocyte TP activity can be derived from the about 4-fold increase in TP activity of the bilateral mixed leukocyte culture relative to the individually cultured controls after 7 days of incubation. TP activity was associated selectively with the monocytes in a PPD-stimulated culture of MNL. The PPD-specific enhancing effect on the leukocyte TP activity could be transferred by soluble factor(s) from stimulated lymphocytes to purified monocytes, which suggests that the effect is, at least partially, mediated by lymphokine(s).
Asunto(s)
Coagulación Sanguínea , Activación de Linfocitos , Monocitos/metabolismo , Tromboplastina/metabolismo , Tuberculina/inmunología , Humanos , Prueba de Cultivo Mixto de LinfocitosRESUMEN
In vitro activity of LB10522 was compared with those of cefpirome, ceftazidime, ceftriaxone, and cefoperazone against clinical isolates. Against gram-positive bacteria, LB10522 was most active among the compounds tested. It was fourfold more active than cefpirome against methicillin-susceptible Staphylococcus aureus and Enterococcus faecalis. LB10522 was highly effective against most members of the family Enterobacteriaceae tested. Ninety percent of isolates of Escherichia coli, Klebsiella oxytoca, Proteus vulgaris, Proteus mirabilis, and Salmonella spp. were inhibited at a concentration of < or = 0.5 micrograms/ml. These activities were comparable to those of cefpirome. Against Pseudomonas aeruginosa, LB10522 with a MIC at which 90% of the isolates are inhibited of 2 micrograms/ml was 16- and 32-fold more active than ceftazidime and ceftazidime against systemic infections caused by Staphylococcus aureus giorgio, Streptococcus pneumoniae III, Pseudomonas aeruginosa 1912E, Escherichia coli 851E, Proteus mirabilis 1315E, Serratia marcescens 1826E, and Acinetobacter calcoaceticus Ac-54. LB10522 was very resistant to hydrolysis by various beta-lactamases such as TEM-3, TEM-7, SHV-1, FEC-1, and P-99. LB10522 did not induce beta-lactamase in Enterobacter cloacae 1194E, although most of the reference cephalosporins acted as inducers of beta-lactamase in this strain. Time-kill study showed that LB10522, at concentrations of two or four times the MIC, had a rapid bactericidal activity against Staphylococcus aureus 6538p, Escherichia coli 851E, and Pseudomonas aeruginosa 1912E.
Asunto(s)
Cefalosporinas/farmacología , Bacterias Gramnegativas/efectos de los fármacos , Bacterias Grampositivas/efectos de los fármacos , Animales , Cefalosporinas/metabolismo , Cefalosporinas/uso terapéutico , Estabilidad de Medicamentos , Enterobacteriaceae/efectos de los fármacos , Inducción Enzimática , Infecciones por Bacterias Gramnegativas/tratamiento farmacológico , Infecciones por Bacterias Gramnegativas/microbiología , Infecciones por Bacterias Grampositivas/tratamiento farmacológico , Infecciones por Bacterias Grampositivas/microbiología , Masculino , Ratones , Ratones Endogámicos ICR , Pruebas de Sensibilidad Microbiana , beta-Lactamasas/biosíntesis , beta-Lactamasas/metabolismoRESUMEN
The deposition of fibrin on infected vegetations and the presence of mononuclear phagocytes that have phagocytized bacteria are remarkabe features in experimental bacterial endocarditis. In a study in vitro, we show that phagocytosis of bacteria by human monocytes enhances thromboplastin generation by these cells. Maximal enhancement of the generation of thromboplastin by monocytes was about six times compared with that in the control experiment without bacteria, and it was obtained by preincubation of the monocytes with 5 to 10 bacteria per monocyte. No quantitative difference was observed between Staphylococcus epidermidis and Streptococcus sanguis as to the enhancement of the monocyte thromboplastin generation. An enhancement of the procoagulant activity generation was also observed after addition of bacteria to human or rabbit whole blood. Probably, this generation was also due to synthesis of thromboplastin by monocytes. It is conceivable that fibrin deposition on infected vegetations during bacterial endocarditis is mediated by thromboplastin synthesis by monocytes.
Asunto(s)
Endocarditis Bacteriana/sangre , Fibrina/metabolismo , Monocitos/metabolismo , Fagocitosis , Tromboplastina/biosíntesis , Animales , Humanos , Técnicas In Vitro , Biosíntesis de Proteínas , Conejos , Staphylococcus , Streptococcus sanguisRESUMEN
LB10517 is a new injectable cephalosporin with a broad spectrum of antibacterial activity against Gram-positive and Gram-negative bacteria. LB10517 inhibited 90% of methicillin-susceptible Staphylococcus aureus (MSSA) at 0.25 mg/L (MIC90), and was 8-fold more active than cefpirome. LB10517 was two- or four-fold more active than cefpirome against methicillin-susceptible Staphylococcus epidermidis (MSSE), Streptococcus pyogenes and Enterococcus faecalis. Both methicillin-resistant S. aureus (MRSA) and methicillin-resistant S. epidermidis (MRSE) were highly resistant to all compounds. LB10517 activity against most Enterobacteriaceae was comparable to or greater than that of cefpirome, and it also showed high activity against Pseudomonas aeruginosa. In a mouse septicaemia model, LB10517 exhibited excellent protective effects. In a respiratory tract infection model, the protective effect of LB10517 was comparable to that of cefpirome and ceftazidime. It was highly stable to hydrolysis by beta-lactamases, showing better physiological efficiency for TEM-9 than the other test compounds. LB10517 had the most potent antibacterial activity against beta-lactamase producing resistant strains. LB10517 did not induce beta-lactamase production in Enterobacter cloacae 1194E.