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31.
Esther Senn Erwin Scharrer Siegfried Wolffram 《Biological trace element research》1992,33(1-3):103-108
The influence of glutathione (1 mmol/L) (GSH) on in vitro mucosal uptake and in vivo absorption of75Se-labeled selenite (10 μmol/L) was investigated in rat jejunum. For comparison, the effect ofl-cysteine (1 mmol/L) on in vivo absorption of75Se-labeled selenite was also studied. In the in vitro, uptake experiments, only the mucosal surface was exposed to the incubation
medium for 3 min. For the in vivo experiments, a luminal perfusion technique was employed. GSH inhibited in vitro mucosal
Se uptake, whereas absorption in vivo was stimulated by GSH.l-Cysteine also stimulated in vivo Se absorption, confirming former in vitro mucosal uptake experiments. Thus, unlikel-cysteine, GSH affected in vitro and in vivo absorption of Se from selenite differently. Enzymatic cleavage of products of
the reaction of selenite with GSH occuring more efficiently under in vivo than in vitro conditions may be a prerequisite for
the stimulatory effect of GSH on Se absorption. This apparently does not apply to the stimulatory effect of cysteine. Since,
GSH occurs in the intestinal lumen under physiological conditions, it may contribute to the high bioavailability of Se from
selenite. 相似文献
32.
Erwin Scharrer Esther Senn Siegfried Wolffram 《Biological trace element research》1992,33(1-3):109-120
The influence of several thiols (conc. 1 mmol/L) on mucosal uptake of75Se from75Se-labeled selenite (conc. 10 μmol/L) across the brush border of rat jejunum and cecum was investigated in vitro using a short-term
uptake technique.l-Cysteine (l-Cys) stimulated75Se uptake in the mid- and distal jejunum and cecum, but not in the proximal jejunum. The effect was maximal in the distal
jejunum.d-Cys was less effective in the jejunum and similarly effective in the cecum.l-Leucine (l-Leu) andl-glutamic acid significantly reduced the stimulatory effect ofl-Cys on Se uptake in the distal jejunum, whereas the respective effect ofd-Cys was not diminished byl-Leu. Cysteamine stimulated mucosal75Se uptake at all intestinal sites tested, whereas the effect of mercaptopyruvate was restricted to the distal jejunum. Thioglycolate
also enhanced75Se uptake in the distal jejunum. The stimulatory effects ofl-Cys, mercaptopyruvate, and thiologlycolate were Na+-dependent, whereas the effect of cysteamine also occurred in the absence of Na+. Mercaptosuccinate,d-penicillamine, ergothioneine, and thiosulfate did not enhance mucosa75Se uptake. It is concluded from these findings that the reaction of some thiols with selenite results in Se compounds that
are rapidly absorbed by the intestinal epithelium through various Na+-dependent and Na+-independent, mechanisms. The high bioavailability of Se from selenite found by others might thus be the result of the presence
of thiols in the gastrointestinal tract. 相似文献
33.
Sanaa Hamdy Omar Siegfried Honecker Hans-Jürgen Rehm 《Applied microbiology and biotechnology》1992,36(4):518-524
Summary The formation of citric acid, oxalic acid, erythritol and glycerol by three strains of Aspergillus niger immobilized in calcium alginate was investigated and compared with that of free cells when cultivated in shake flasks under phosphate limitation. Morphological changes were followed using an electron microscope. The production of acids and polyols, the consumption of glucose and fructose, and also the morphological changes were strain-dependent. The results also reflected the influence of long storage of a strain on productivity, morphological behaviour and phosphate consumption.
Offprint requests to: H.-J. Rehm 相似文献
34.
Gerry T. Snoek Cees H. Koster Siegfried W. de Laat Martin Heideveld Antony J. Durston Everardus J. J. van Zoelen 《Experimental cell research》1990,187(2)
The Xenopus laevis XTC cell line has been analyzed for the production of polypeptide growth factors and mesoderm-inducing activity. By the use of specific biological assays, it is shown that XTC cells produce a growth factor functionally related to the platelet-derived growth factor (PDGF) and two transforming growth factor (TGF)β-like activities. Mesoderm-inducing activity, as measured on X. laevis ectodermal explants from stage 10 embryos, was found to coelute on a Bio-Gel P-100 column with one of the TGFβ-like activities at an apparent molecular weight of 6–10 kDa. Analysis of the DNA content from XTC cells by flow cytometry demonstrated that the cell line is heterogeneous and consists of both tetraploid and diploid cells. Cloning of the XTC cells and selecting single-cell colonies on the basis of their ability to grow in soft agar resulted in the isolation of several homogeneous, morphologically different clonal derivatives. Analysis of conditioned medium from these clonal derivatives showed that only one of them, the only diploid line among six investigated, produced a strong heat- and acid-stable mesoderm-inducing activity that induced notochord and muscle formation in stage 10 X. laevis ectodermal expiants. The relation between this activity and a recently described TGFβ-like mesoderm-inducing factor obtained from XTC-conditioned medium will be discussed. In conclusion, a clonal cell line derived from X. laevis XTC cells which provides a good source for further characterization of mesoderm-inducing factors has been established. 相似文献
35.
Summary In South Africa seedlings of the exotic Acacia cyclops grow in clumps. The seedlings occur beneath tall elements, or in bush clumps, of the surrounding indigenous vegetation. The tall shrubs are used as perches by birds, and the pattern of seedling distribution is a result of dispersal of seeds by birds. Germination of A. cyclops seeds was enhanced as a result of passage through the gut of a bird, or by artificial treatments simulating actions taking place in the gut of a bird. We examine properties of the seed, and the funicle which is attractive to birds, in relation to aspects of the life history of A. cyclops and the species' success as an invasive plant in South Africa. 相似文献
36.
Johannes Boonstra Paul T. Van Der Saag Wouter H. Moolenaar Siegfried W. De Laat 《Experimental cell research》1981,131(2):452-455
Nerve growth factor (NGF) induces neuronal differentiation of rat pheochromocytoma cells (PC12). Here we show that NGF causes a stimulation of Na+,K+-pump mediated K+ influx, with a maximum at 30 min after addition of NGF. The stimulation of the Na+,K+-pump is completely blocked by the Na+-flux inhibitor amiloride (0.2 mM) and can be mimicked by the Na+ ionophore monensin. These results suggest that NGF causes a rapid enhancement of Na+ influx leading to an activation of the Na+,K+-pump, a mechanism similar to the action of other growth factors. 相似文献
37.
Using a battery of seven lectin-ferritin conjugates as probes for cell surface glycoconjugates, we have studied the pattern of plasmalemmal differentiation of cells in the embryonic rat pancreas from day 15 in utero to the early postpartum stage. Our results indicate that differentiation of plasmalemmal glycoconjugates on acinar, endocrine, and centroacinar cells is temporally correlated with development and is unique for each cell type, as indicated by lectin-ferritin binding. Specifically, (a) expression of adult cell surface saccharide phenotype can be detected on presumptive acinar cells as early as 15 d in utero, as indicated by soybean agglutinin binding, and precedes development of intracellular organelles characteristic of mature acinar cells; (b) maturation of the plasmalemma of acinar cells is reached after intracellular cytodifferentiation is completed, as indicated by appearance of Con A and fucoselectin binding sites only at day 19 of development; conversely, maturation of the endocrine cell plasmalemma is accompanied by "loss" (masking) of ricinus communis II agglutinin receptors; and (c) binding sites for fucose lectins and for soybean agglutinin are absent on endocrine and centroacinar cells at all stages examined. We conclude that acinar, centroacinar, and endocrine cells develop from a common progenitor cell(s) whose plasmalemmal carbohydrate composition resembles most closely that of the adult centroacinar cell. Finally, appearance of acinar lumina beginning at approximately 17 d in utero is accompanied by differenetiation of apical and basolateral plasmalemmal domains of epithelial cells, as indicated by enhanced binding of several lectin-ferritin conjugates to the apical plasmalemmal, a pattern that persists from this stage through adult life. 相似文献
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