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We have previously reported that theSaccharomyces cerevisiae CRS5 metallothionein gene is negatively regulated by oxygen. The mechanism of this repression was the focus of the current study. We observed that the aerobic repression ofCRS5 is rapid and occurs within minutes of exposing anaerobic cultures to air. Furthermore, theCUP1 metallothionein gene ofS. cerevisiae was found to be subject to a similar down-regulation of gene expression. We provide evidence that the aerobic repression of yeast metallothioneins involves copper ions and Ace1, the coppertrans-activator ofCUP1 andCRS5 gene expression. A functional Ace1 binding site was found to be necessary for the aerobic repression ofCRS5. Moreover, the aerobic down-regulation of the metallothioneins was abolished when cells were treated with elevated levels of copper. Our studies show that anaerobic cultures accumulate higher levels of copper than do aerobic cells and that this copper is rapidly lost when cells are exposed to air. In fact, the kinetics of this copper loss closely parallels the kinetics ofCUP1 andCRS5 gene repression. The yeast metallothionein genes, therefore, serve as excellent markers for variations in copper accumulation and homeostasis that occur in response to changes in the oxidative status of the cell. 相似文献
103.
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
104.
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
105.
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
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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