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81.
Anaerobic enrichment culture of flooded soil and river sediment demonstrated that 2,2-dichloropropionate can be degraded by a methanogenic route. 相似文献
82.
There are two major domains of interaction between the Escherichia coli release factors (RF-1 and RF-2) and each subunit of the ribosome. RF-2 has a binding domain on the shoulder and lower head region of the small subunit at the small lobe distant from the decoding site. This is in close proximity to one of the domains on the large subunit which includes the body dimer of L7/L12 and L11. The other domains of interaction, at the decoding site on the small subunit, and at the peptidyltransferase centre of the large subunit of the ribosome, are some distance from the first two, although the evidence for direct contact with the ribosome is less comprehensive. The release factors may therefore have two distinct structural domains, and in support of this concept RF-1 and RF-2 can both be cleaved into two fragments by papain. Region-specific antibodies, and antibodies against defined peptide within the RF sequences have given an indication that a significant part of an interacting RF molecule is in close proximity to the ribosome surface, confirming an observation by immunoelectron microscopy which suggested that the RF penetrates deeply into the cleft between the two subunits. A region of highly conserved primary sequence between the two release factors from E coli is also conserved in those from B subtilis suggesting it forms an important structural or functional domain. Antibodies against peptides from the N-terminal end of this region strongly inhibit binding of the RF to the ribosome. 相似文献
83.
R. Shainkin-Kestenbaum C. Caruso G. M. Berlyne 《Biological trace element research》1991,28(3):213-221
The effect of nickel on superoxide dismutase activity (SOD), as well as on rate of hydroxydopamine oxidation, was studied in vitro since lipid peroxidation has been implicated in cell damage by nickel, whose toxicity and carcinogenicity are well established. Nickel strongly inhibits SOD activity. The degree of inhibition is directly proportion to the nickel concentration (tested range 0.066 to 0.33 microgram/mL in the reaction mixture); to the substrate concentration (tested range 0.4 x 10 4M to 1.1 x 10 4M 6-hydroxydopamine); and to reaction mixture. Autoxidation of 6-hydroxydopamine was increased by nickel concentrations higher than 15 micrograms/mL. The combination of excessive oxygen free radical production and inhibition of their elimination by inhibition of SOD activity may contribute to the nickel toxicity that has been reported in industrial accidents, as well as to the high incidence of cancer occurring in nickel workers. It may also contribute to many complications in uremic patients, in whom increased serum nickel levels were reported to be in a similar range to those inhibiting SOD. 相似文献
84.
85.
Amylin, a 37-residue polypeptide with a single disulfide bond originally isolated from the pancreas of type-II diabetic patients, has been shown to cause peripheral insulin resistance and to attenuate the inhibition of hepatic glucose output by insulin. We have also shown that amylin is present in the rat hypothalamus and that it inhibits food intake by rats. In order to further investigate the anorectic properties we synthesized both human and rat amylin by the solid phase method and purified to homogeneity in an overall yield of 10-20%. Structural analyses indicated that human amylin exhibited predominantly a beta-sheet structure at both acidic and alkaline pH, whereas no ordered structure was evident in the case of rat amylin. Intrahypothalamic injection of rat amylin resulted in a potent dose-dependent inhibitory effect on the food intake by rats adapted to eat their daily ration of food in an eight-hour period. Human amylin was less effective as an anorectic agent. Furthermore, rat amylin completely blocked the potent orexigenic effect of neuropeptide Y (NPY). These investigations show that there is a fundamental difference in the secondary structures of human and rat amylin and that rat amylin is a potent inhibitor of both basal and NPY-induced feeding by rats. 相似文献
86.
Flow cytometry sorting of viable bacteria and yeasts according to beta-galactosidase activity. 总被引:5,自引:2,他引:3 下载免费PDF全文
We describe a novel method for quantitative measurement of beta-galactosidase (beta-gal) levels in bacteria and yeasts by using flow cytometry, a method which allows viable microbial cells to be sorted on the basis of the expressed activity and to be recultivated. The method is based on encapsulating single cells in agarose microbeads 20 to 30 microns in diameter and analyzing the beta-gal activity of the colonies that develop (containing several hundred cells) by using the fluorogenic substrate fluorescein-di-beta-D-galactopyranoside (FDG). Three strains of Escherichia coli, containing different levels of beta-gal, served as a model system. A high degree of correlation was found between the average fluorescence measured per bead and the level of the enzyme in extracts of the respective strain. Although the use of FDG necessitates cell permeabilization, conditions were found under which a small part of each colony remained viable, yet most of the enzyme was exposed to the substrate. This allowed sorting of microcolonies and plating with close to 100% efficiency. The potential of the technique was demonstrated by selecting beta-gal-positive cells from an artificial mixture of beta-gal-positive and beta-gal-negative E. coli strains. 相似文献
87.
Fluorescence detection of enzymatically formed hydrogen peroxide in aqueous solution and in reversed micelles 总被引:7,自引:0,他引:7
A sensitive enzymatic assay for oxidase reactions both in aqueous solution and in hexadecyltrimethylammoniumbromide (CTAB) reversed micelles has been developed. The assay is based on the fluorescence detection of dichlorofluorescein, which is formed by hydrogen peroxide oxidation of the nonfluorescent precursor dichlorofluorescin. Hydrogen peroxide as product of the reaction catalyzed by glucose oxidase served to select the reaction conditions. The reaction rate is distinctly enhanced in CTAB reversed micelles as compared to the rate in aqueous solution. This effect, combined with the high sensitivity owing to the strong fluorescence of dichlorofluorescein, makes the assay attractive for the detection of low enzyme, substrate, or peroxide concentrations. 相似文献
88.
Interactions between water availability and elevated atmosphericCO2 concentrations have the potential to be important factorsin determining future forage supply from temperate pastures.Using large turves from an established pasture, the responseof these communities at 350 or 700 l l1 CO2 to a soilmoisture deficit and to recovery from the deficit in comparisonto turves that were well-watered throughout was measured. Priorto this experiment the turves had been exposed to the CO2 treatmentsfor 324 d. Net CO2 exchange continued at elevated CO2 even when the volumetricsoil moisture content was less than 0.10 m3 m3 soil;at the same moisture deficit gas exchange at ambient CO2 waszero. The additional carbon fixed by the elevated CO2 turveswas primarily allocated below-ground as shown by the maintenanceof root length density at the same level as in well-wateredturves. When the dry turves were rewatered there was compensatorygrowth at ambient CO2 so that the above-ground growth rate exceededthat of turves that had not experienced a moisture deficit.At the start of this experiment, the turves that were growingat 700 l I1 CO2 had a greater proportion of legume (principallywhite clover, Trifolium repens L.) in the harvested herbage.There was a trend for the legume content at elevated CO2 tobe reduced under a soil moisture deficit. The results indicate different strategies in response to soilmoisture deficits depending on the CO2 concentration. At ambientCO2, growth stopped, but plants were able to respond stronglyon rewatering; while at elevated CO2 growth continued (particularlybelow-ground), but no additional growth was evident on rewatering.Ecosystem gas exchange measurements taken at the end of theexperiment (after 429 d of exposure to CO2) showed 33% moreCO2 was fixed at elevated CO2 with only a small (12%) and nonsignificantdownward regulation. Key words: Carbon dioxide, climate change, grassland, gas exchange, soil moisture deficit 相似文献
89.
90.
Alterations of auxin perception in rolB-transformed tobacco protoplasts. Time course of rolB mRNA expression and increase in auxin sensitivity reveal multiple control by auxin. 总被引:2,自引:0,他引:2 下载免费PDF全文
C Maurel N Leblanc H Barbier-Brygoo C Perrot-Rechenmann M Bouvier-Durand J Guern 《Plant physiology》1994,105(4):1209-1215
Expression and physiological effects of the root-inducing rolB gene of Agrobacterium rhizogenes T-DNA were studied simultaneously in tobacco (Nicotiana tabacum) mesophyll protoplasts. The kinetic study of the expression of rolB mRNA following exogenous auxin application showed that auxin transiently stimulated rolB expression, with mRNA levels starting to accumulate 6 to 9 h after auxin was supplied and increasing 300-fold after 12 to 18 h. The parallel study of the auxin sensitivity of rolB-transformed protoplasts, as assayed by their electrical response to the hormone, showed that the auxin treatment generated an increase in sensitivity by a factor of up to 100,000, whereas in untransformed protoplasts the same auxin treatment induced an increase in auxin sensitivity that never exceeded 30- to 50-fold. This reflects a strong cooperative effect of auxin and rolB in transformed protoplasts. Surprisingly, the maximal increase in sensitivity was observed several hours before the maximal accumulation of rolB mRNA, suggesting that the dramatic control of auxin sensitivity by auxin in rolB-transformed protoplasts requires only low levels of rolB expression. Antibodies directed against ZmER-abp1, the major auxin-binding protein from maize, differentially altered the auxin sensitivity of the electrical response of rolB-transformed and normal protoplasts. This suggests that alterations of the auxin reception-transduction pathway at the plasma membrane of rolB-transformed protoplasts may account for their increased auxin sensitivity. 相似文献