RESUMEN
Xyloglucans from seeds of Copaifera langsdorffii (XGC), Hymenaea courbaril (XGJ) and Mucuna sloanei (XGM) were obtained from milled and defatted cotyledons by aqueous extraction at 25 degrees C. The resulting fractions contained Glc, Xyl and Gal in molar ratios of 2.5: 1.5: 1.0 (XGC), 3.8: 2.6: 1.0 (XGJ) and 2.5: 1.6: 1.0 (XGM). HPSEC-MALLS/RI analysis showed that each polysaccharide fraction was homogeneous; M(w) values were 1.6 x 10(5), 2.0 x 10(5) and 1.5 x 10(5)g/mol, respectively. The effect of the xyloglucans on the production of O(2)*(-) and NO* and on the recruitment of macrophages to the mouse peritoneum was evaluated. All polysaccharides promoted an increase in the number of peritoneal macrophages in a dose-dependent manner. The largest increase, of 576% in comparison to the control group, was elicited by XGJ at 200 mg/kg. The effect of XGC, XGJ and XGM on O(2)*(-) production, in the presence or absence of phorbol 12-myristate 13-acetate (PMA), was not statistically significant. For NO(.) production, the lowest concentration of XGC (10 microg/ml) gave rise to an increase of 262% when compared to the control group; the effect was dose-dependent, reaching 307% at 50 microg/ml. On the other hand, XGJ at a concentration of 50 microg/ml enhanced NO* production by 92%. XGM did not affect NO* production significantly. The results indicate that xyloglucans from C. langsdorffii, H. courbaril and M. sloanei have immunomodulatory activity.
Asunto(s)
Glucanos/farmacología , Macrófagos Peritoneales/efectos de los fármacos , Xilanos/farmacología , Animales , Células Cultivadas , Cromatografía en Gel , Glucanos/química , Macrófagos Peritoneales/metabolismo , Ratones , Monosacáridos/química , Dióxido de Nitrógeno/metabolismo , Superóxidos/metabolismo , Xilanos/químicaRESUMEN
The kinetic energy of superconducting electrons in an ultrathin, doubly connected superconducting cylinder, determined by the applied flux, increases as the cylinder diameter decreases, leading to a destructive regime around half-flux quanta and a superconductor to normal metal quantum phase transition (QPT). Regular steplike features in resistance versus temperature curves taken at fixed flux values were observed near the QPT in ultrathin Al cylinders. It is proposed that these features are most likely resulting from a phase separation near the QPT in which normal regions nucleate in a homogeneous superconducting cylinder.
RESUMEN
We report the first systematic study of the electrical transport and magnetic properties of BaRu6O12, which has a quasi-one-dimensional (quasi-1D) hollandite structure. We show that BaRu6O12 is quasi-1D electronically as well. Its physical properties were found to be extremely sensitive to disorder. Furthermore, a transition from being metallic with a resistance drop around 2 K to being weakly insulating as the applied magnetic field was increased was also found. We propose that these two features are related to the possible presence of a quantum phase transition in this material system.
RESUMEN
In doubly connected superconductors, such as hollow cylinders, the fluxoid is known to be quantized, allowing the superfluid velocity to be controlled by an applied magnetic flux and the sample size. The sample-size-induced increase in superfluid velocity has been predicted to lead to the destruction of superconductivity around half-integer flux quanta. We report transport measurements in ultrathin Al and Au0.7In0.3 cylinders verifying the presence of this destructive regime characterized by the loss of the global phase coherence and reveal a phase diagram featuring disconnected phase coherent regions, as opposed to the single region seen in larger superconducting cylinders studied previously.
RESUMEN
In this study, we have demonstrated that two unique proteins in Bacillus subtilis chemotaxis, CheC and CheD, interact. We have shown this interaction both by using the yeast two-hybrid system and by precipitation of in vitro translated products using glutathione-S-transferase fusions and glutathione agarose beads. We have also shown that CheC inhibits B. subtilis CheR-mediated methylation of B. subtilis methyl-accepting chemotaxis proteins (MCPs) but not of Escherichia coli MCPs. It was previously reported that cheC mutants tend to swim smoothly and do not adapt to addition of attractant; cheD mutants have very poorly methylated MCPs and are very tumbly, similar to cheA mutants. We hypothesize that CheC exerts its effect on MCP methylation in B. subtilis by controlling the binding of CheD to the MCPs. In absence of CheD, the MCPs are poor substrates for CheR and appear to tie up, rather than activate, CheA. The regulation of CheD by CheC may be part of a unique adaptation system for chemotaxis in B. subtilis, whereby high levels of CheY-P brought about by attractant addition would allow CheC to interact with CheD and consequently leave the MCPs, reducing CheA activity and hence the levels of CheY-P.
Asunto(s)
Bacillus subtilis/metabolismo , Proteínas Bacterianas/metabolismo , Quimiotaxis , Proteínas de la Membrana/metabolismo , Anticuerpos Antibacterianos/metabolismo , Bacillus subtilis/genética , Proteínas Bacterianas/genética , Proteínas de Escherichia coli , Histidina Quinasa , Proteínas Quimiotácticas Aceptoras de Metilo , Metilación , Proteínas Recombinantes de Fusión/genética , Proteínas Recombinantes de Fusión/aislamiento & purificación , Proteínas Recombinantes de Fusión/metabolismoRESUMEN
We characterized mutants in two novel genes of Bacillus subtilis, cheC and cheD. Mutants in CheC had a high smooth swimming bias and exhibited poor adaptation to positive stimuli. Analysis of tethered cells revealed two distinct subpopulations which differ in their prestimulus bias and extent of adaptation. The receptors, the methyl-accepting chemotaxis proteins (MCPs), of this mutant strain were overmethylated, as a result of an increase in CheR activity. We speculate that CheC helps to control tumbling frequency by regulating CheR, perhaps by a feedback mechanism through the MCPs. In contrast, a cheD mutant exhibited very tumbly behavior, and many of the MCPs were unmethylated. It seems that some B. subtilis MCPs require the presence of CheD for CheR to methylate them, a unique feature of B. subtilis chemotaxis. It is hypothesized that CheD is part of a complex that facilitates methylation of some of the MCPs, and dissociation of CheD from this complex affects CheA activity and may help bring about adaptation.
Asunto(s)
Bacillus subtilis/citología , Proteínas Bacterianas , Quimiotaxis , Proteínas de la Membrana/fisiología , Quimiotaxis/genética , Clonación Molecular , Escherichia coli/genética , Proteínas de Escherichia coli , Prueba de Complementación Genética , Histidina Quinasa , Proteínas de la Membrana/genética , Proteínas Quimiotácticas Aceptoras de Metilo , Metilación , Metiltransferasas/metabolismo , MutaciónRESUMEN
We report the sequence and characterization of the Bacillus subtilis tlpC gene. tlpC encodes a 61.8 kDa polypeptide (TlpC) which exhibits 30% amino acid identity with the Escherichia coli methyl-accepting chemotaxis proteins (MCPs) and 38% identity with B. subtilis MCPs within the C-terminal domain. The putative methylation sites parallel those of the B. subtilis MCPs, rather than those of the E. coli receptors. TlpC is methylated both in vivo and in vitro although the level of methylation is poor. In addition, the E. coli anti-Trg antibody is shown to cross-react with this membrane protein. Inactivation of the tlpC gene confirms that TlpC is not one of the previously characterized MCPs from B. subtilis. Capillary assays were performed using a variety of chemoeffectors, which included all 20 amino acids, several sugars, and several compounds previously classified as repellents. However, no chemotactic defect was observed for any of the chemoeffectors tested. We suggest that TlpC is similar to an evolutionary intermediate from which the major chemotactic transducers from B. subtilis arose.
Asunto(s)
Bacillus subtilis/química , Proteínas Bacterianas/aislamiento & purificación , Genes Bacterianos , Secuencia de Aminoácidos , Bacillus subtilis/genética , Proteínas Bacterianas/genética , Secuencia de Bases , Escherichia coli/química , Proteínas de la Membrana/química , Proteínas Quimiotácticas Aceptoras de Metilo , Metilación , Datos de Secuencia Molecular , Sistemas de Lectura Abierta , Alineación de Secuencia , Homología de Secuencia de AminoácidoRESUMEN
We have characterized mutants in a novel gene of Bacillus subtilis, cheV, which encodes a protein homologous to both CheW and CheY. A null mutant in cheV is only slightly defective in capillary and tethered cell assays. However, a double mutant lacking both CheV and CheW has a strong tumble bias, does not respond to addition of attractant, and shows essentially no accumulation in capillary assays. Thus, CheV and CheW appear in part to be functionally redundant. A strain lacking CheW and expressing only the CheW domain of CheV is chemotactic, suggesting that the truncated CheV protein retains in vivo function. We speculate that CheV and CheW function together to couple CheA activation to methyl-accepting chemotaxis protein receptor status and that possible CheA-dependent phosphorylation of CheV contributes to adaptation.