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A H Verschoor-Klootwyk L Verschoor S Azhar G M Reaven 《The Journal of biological chemistry》1982,257(13):7666-7671
Rat steroidogenic tissues take up cholesterol, and it has been suggested that this process plays a regulatory role in steroid hormone synthesis. To provide evidence for this hypothesis, we carried out studies in lipoprotein-deficient rats. Lipoprotein deficiency, achieved by treating male rats with pharmacological amounts of estradiol, led to profound lowering of plasma cholesterol (8 +/- 2 versus 54 +/- 4 mg/dl) and adrenal cholesteryl ester content (113 +/- 57 versus 747 +/- 108 micrograms/organ). Basal serum corticosterone levels were decreased by 50%, and the response to adrenocorticotropic hormone (ACTH) was totally abolished. Injection of high density lipoprotein (HDL) to estradiol-treated animals restored the response of corticosterone to ACTH. Comparable in vitro studies with adrenal cell suspensions obtained from lipoprotein-deficient rats confirmed the in vivo data. Measurement of [14C]acetate incorporation and uptake of both HDL- and low density lipoprotein (LDL)-cholesterol in these adrenal cells showed a progressive increase with the duration of estradiol treatment, and neither of these two phenomena was altered by ACTH. These results provide in vitro and in vivo evidence for the hypothesis that normal adrenal steroidogenesis depends upon cholesterol delivery from plasma. Furthermore, under the conditions studied, ACTH does not stimulate adrenal de novo cholesterol biosynthesis nor the uptake of either HDL- or LDL-cholesterol. 相似文献
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Multivariate statistical analysis of ribosome electron micrographs. L and R lateral views of the 40 S subunit from HeLa cells 总被引:7,自引:0,他引:7
The morphology of the small (40 S) subunit of the eukaryotic ribosome from HeLa cells has been examined by single-particle averaging and multivariate image analysis applied to electron micrographs of negatively stained specimens. The use of multivariate image analysis allows different, independent components of the structural variation within the particles to be identified and separately studied. The largest component of variance for both lateral views (termed L and R) was the variation in the peripheral stain intensity. The second largest component of interparticle variation is due to changes in the particle appearance most likely associated with a change of orientation on the specimen film.Averages formed from particles falling within a small range of peripheral stain intensity allowed the changes in the projected structure to be studied as a function of local stain level. Visual observations of stain variation could be confirmed quantitatively.Significant differences were found between averages of particles in the L view and those in the R view. Multivariate image analysis of a mixed population of L and mirrored R particles showed that the differences consistently affect all particles. However, the R view increasingly resembles the L view as the overall level of stain is increased, in agreement with a model of partial stain immersion. 相似文献
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The effects of lowering the pH on Photosystem II have been studied by measuring changes in absorbance and electron spin resonance in spinach chloroplasts.At pH values around 4 a light-induced dark-reversible chlorophyll oxidation by Photosystem II was observed. This chlorophyll is presumably the primary electron donor of system II. At pH values between 5 and 4 steady state illumination induced an ESR signal, similar in shape and amplitude to signal II, which was rapidly reversed in the dark. This may reflect the accumulation of the oxidized secondary donor upon inhibition of oxygen evolution. Near pH 4 the rapidly reversible signal and the stable and slowly decaying components of signal II disappeared irreversibly concomitant with the release of bound manganese.The results are discussed in relation to the effects of low pH on prompt and delayed fluorescence reported earlier (van Gorkom, H. J., Pulles, M. P. J., Haveman, J. and den Haan, G. A. (1976) Biochim. Biophys. Acta 423, 217–226). 相似文献
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Marijn Rutgers Daniël BF Saris Wouter JA Dhert Laura B Creemers 《Arthritis research & therapy》2010,12(3):R114
Introduction
Intraarticular administration of autologous conditioned serum (ACS) recently demonstrated some clinical effectiveness in treatment of osteoarthritis (OA). The current study aims to evaluate the in vitro effects of ACS on cartilage proteoglycan (PG) metabolism, its composition and the effects on synovial fluid (SF) cytokine levels following intraarticular ACS administration. 相似文献7.
The invasive freshwater snail Tarebia granifera (Lamarck, 1822) was first reported in South Africa in 1999 and it has become widespread across the country, with some evidence to suggest that it reduces benthic macroinvertebrate biodiversity. The current study aimed to identify the primary abiotic drivers behind abundance patterns of T. granifera, by comparing the current abundance of the snail in three different regions, and at three depths, of the highly modified Nseleni River in KwaZulu-Natal, South Africa. Tarebia granifera was well established throughout the Nseleni River system, with an overall preference for shallow waters and seasonal temporal patterns of abundance. Although it is uncertain what the ecological impacts of the snail in this system are, its high abundances suggest that it should be controlled where possible and prevented from invading other systems in the region. 相似文献
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The signal produced by fluorescence in situ hybridization (FISH) often is inconsistent among cells and sensitivity is low. Small DNA targets on the chromatin are difficult to detect. We report here an improved nick translation procedure for Texas red and Alexa Fluor 488 direct labeling of FISH probes. Brighter probes can be obtained by adding excess DNA polymerase I. Using such probes, a 30 kb yeast transgene, and the rp1, rp3 and zein multigene clusters were clearly detected. 相似文献
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Water hyacinth Eichhornia crassipes is considered the most damaging aquatic weed in the world. However, few studies have quantified the impact of this weed economically and ecologically, and even fewer studies have quantified the benefits of its control. This paper focuses on water loss saving as the benefit derived from biological control of this plant between 1990 and 2013 at New Year’s Dam, Alicedale, Eastern Cape, South Africa. Estimates of water loss due to evapotranspiration from water hyacinth vary significantly; therefore, the study used three different rates, high, medium and low. A conservative raw agriculture value of R 0.26 per m3 was used to calculate the benefits derived by the water saved. The present benefit and cost values were determined using 10% and 5% discount rates. The benefit/cost ratio at the low evapotranspiration rate was less than one, implying that biological control was not economically viable but, at the higher evapotranspiration rates, the return justified the costs of biological control. However, at the marginal value product of water, the inclusion of the costs of damage to infrastructure, or the adverse effects of water hyacinth on biodiversity, would justify the use of biological control, even at the low transpiration rate. 相似文献
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