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排序方式: 共有352条查询结果,搜索用时 570 毫秒
1.
Ze'ev Barak Bela Ohana Yael Allon Joel Margalit 《Applied microbiology and biotechnology》1987,27(1):88-93
Summary PST, a spontaneous mutant of Bacillus thuringiensis var. israelensis (B.t.i.) resistant to penicillin, streptomycin and tetracycline was isolated by serial selections. In the absence of antibiotics it showed genetic stability for 16 generations. Mosquito larvicidal activity of PST was similar to that of B.t.i., its parental strain. It also maintained the specific antigenicity of B.t.i. although its rate of growth was somewhat lower, a generation time of 55 min for PST vs. 38 min for B.t.i. Cell concentration plays a major role in the phenomenon of PST resistance to penicillin.This antibiotic resistant mutant of b.t.i. provides us with an efficient tool to trace B.t.i. among the indigenous bacteria present in septic habitats in the field as well as inside the larval gut. 相似文献
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In a recent paper (P Ohana, DP Delmer, JC Steffens, DE Matthews, R Mayer, M Benziman [1991] J Biol Chem 266: 13472-13475), we described the purification and structural characterization of β-furfuryl-β-glucoside (FG), an endogenous activator of plant UDP-glucose:(1→3)-β-glucan (callose) synthase. In the present report, we provide evidence that FG specifically stimulates callose synthase. The effects of FG on the kinetic properties of callose synthase were studied, and we ascertained that FG, or at least a very similar compound, is present in other plant systems. Chemically synthesized α-furfuryl-β-glucoside also stimulates callose synthase, exhibiting a slightly higher Ka of 80 micromolar, compared with 50 micromolar for FG. In addition, we have identified and partially characterized an enzyme that catalyzes the synthesis of FG using β-furfuryl alcohol and UDP-glucose as substrates. A model for the regulation of callose synthesis in vivo, involving changes in intracellular compartmentation of FG and Ca2+, is proposed. 相似文献
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Glutaraldehyde has been used for several decades as an effective crosslinking agent for many applications including sample fixation for microscopy, enzyme and cell immobilization, and stabilization of protein crystals. Despite of its common use as a crosslinking agent, the mechanism and chemistry involved in glutaraldehyde crosslinking reaction is not yet fully understood. Here we describe feasibility study and results obtained from a new approach to investigate the process of protein crystals stabilization by glutaraldehyde crosslinking. It involves exposure of a model protein crystal (Lysozyme) to glutaraldehyde in alkaline or acidic pH for different incubation periods and reaction arrest by medium exchange with crystallization medium to remove unbound glutaraldehyde. The crystals were subsequently incubated in diluted buffer affecting dissolution of un-crosslinked crystals. Samples from the resulting solution were subjected to protein composition analysis by gel electrophoresis and mass spectroscopy while crosslinked, dissolution resistant crystals were subjected to high resolution X-ray structural analysis. Data from gel electrophoresis indicated that the crosslinking process starts at specific preferable crosslinking site by lysozyme dimer formation, for both acidic and alkaline pH values. These dimer formations were followed by trimer and tetramer formations leading eventually to dissolution resistant crystals. The crosslinking initiation site and the end products obtained from glutaraldehyde crosslinking in both pH ranges resulted from reactions between lysine residues of neighboring protein molecules and the polymeric form of glutaraldehyde. Reaction rate was much faster at alkaline pH. Different reaction end products, indicating different reaction mechanisms, were identified for crosslinking taking place under alkaline or acidic conditions. 相似文献
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Lee H Hubbert ML Osborne TF Woodford K Zerangue N Edwards PA 《The Journal of biological chemistry》2007,282(30):21653-21661
Fxralpha is known to regulate a variety of metabolic processes, including bile acid, cholesterol, and carbohydrate metabolism. In this study, we show direct evidence that Fxralpha is a key player in maintaining sulfate homeostasis. We identified and characterized the sodium/sulfate co-transporter (NaS-1; Slc13a1) as an Fxralpha target gene expressed in the kidney and intestine. Electromobility shift assays, chromatin immunoprecipitation, and promoter reporter studies identified a single functional Fxralpha response element in the second intron of the mouse Slc13a1 gene. Treatment of wild-type mice with GW4064, a synthetic Fxralpha agonist, induced Slc13a1 mRNA in the intestine and kidney. Slc13a1 mRNA was also induced in the kidney and intestine of wild-type, but not Fxralpha-/- mice, after treatment with the hepatotoxin alpha-naphthylisothiocyanate, which is known to result in elevated blood bile acid levels. Finally, we observed a decrease in Slc13a1 mRNA in the kidney and intestine of Fxralpha-/- mice and a corresponding increase in urinary excretion of free sulfates as compared with wild-type mice. These results demonstrate that mouse Slc13a1 is a novel Fxralpha target gene expressed in the kidney and intestine and that in the absence of Fxralpha, mice waste sulfate into the urine. Thus, Fxralpha is necessary for normal sulfate homeostasis in vivo. 相似文献
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Noa Vaisman 《The journal of the Royal Anthropological Institute》2022,28(Z1):103-117
In Argentina, irreconciliation is created through everyday practices of vigilance against closure and collective struggles against impunity. In this essay, I show how over several decades since the fall of the dictatorial regime (1976-83), human rights activists and laypeople have devised ways to keep the past alive while attending to injustices through embodied collective engagements with the country's history and its legacies. By examining large protests, the everyday experiences of impunity, and a filmic exploration of kinship bonds and their entanglement with civilian complicity in the repression, the essay illustrates the ways in which irreconciliation is materialized and enacted as a form of social reconstruction many years after state terrorism. 相似文献
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Jacquamet L Ohana J Joly J Borel F Pirocchi M Charrault P Bertoni A Israel-Gouy P Carpentier P Kozielski F Blot D Ferrer JL 《Structure (London, England : 1993)》2004,12(7):1219-1225
Crystallogenesis, usually based on the vapor diffusion method, is currently considered one of the most difficult steps in macromolecular X-ray crystallography. Due to the increasing number of crystallization assays performed by protein crystallographers, several automated analysis methods are under development. Most of these methods are based on microscope images and shape recognition. We propose an alternative method of identifying protein crystals: by directly exposing the crystallization drops to an X-ray beam. The resulting diffraction provides far more information than classical microscope images. Not only is the presence of diffracting crystals revealed, but also a first estimation of the space group, cell parameters, and mosaicity is obtained. In certain cases, it is also possible to collect enough data to verify the presence of a specific substrate or a heavy atom. All these steps are performed without the sometimes tedious necessity of removing crystals from their crystallization drop. 相似文献
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This study investigates the anatomical aspects of heavy-metal accumulation in the waterlily (Nymphaea `Aurora', Nymphaeaceae). Epidermal glands were identified by light microscopy on the abaxial side of the leaf laminae and
on the epidermis of the rhizome; glandular trichomes were observed in the petiole epidermis. Glands were not observed in the
roots. Accumulation of heavy metals in these glands was monitored using a scanning electron microscope equipped for energy-dispersive
spectroscopy. Further experiments showed maximal cadmium and calcium accumulation in the mature leaf lamina in daylight, and
this accumulation was inhibited by the herbicide 3-(3′,4′-dichlorophenyl)-1,1-dimethylurea. These results suggest that, in
Nymphaea, heavy metals are accumulated primarily in association with glands found in plant organs that have direct contact with water
or mud. Deposition and storage of heavy metals by these glands may represent a stage in the sequestration and detoxification
of the metals. Our results raise the possibility of utilizing waterlilies for the removal of heavy metals from polluted environments.
Received: 29 April 2000 / Accepted: 8 June 2000 相似文献
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