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991.
Abstract: Galactosylceramide ("galactocerebroside"; GalC) is a major glycolipid in the myelin sheath of the CNS and the PNS. The enzyme UDP-galactose:ceramide galactosyltransferase (CGalT) catalyzes the final step of the synthesis of GalC: the transfer of galactose to ceramide. By a differential screening approach, we have isolated a cDNA, the sequence of which is identical to the recently isolated cDNA clones for CGalT. By northern analysis and in situ hybridization we demonstrated that CGalT mRNA is expressed at birth in oligodendrocytes and Schwann cells, an expression pattern corresponding to the onset of myelination. In addition to the high expression levels of CGalT in oligodendrocytes and Schwann cells, in situ hybridization also showed expression in subtypes of neurons in spinal cord, cerebellum, and brainstem in the adult CNS, but at a much lower level than in oligodendrocytes. Expression of CGalT in COS cells demonstrated that CGalT has a preference for hydroxyceramide as a substrate. CGalT-expressing COS cells synthesize and transport GalC to their cell surface as shown by immunofluorescence and by lipid analysis of living cells. Our results suggested that the CGalT specifically uses hydroxyceramide for the synthesis of GalC and that separate (co)enzymes are not needed. 相似文献
992.
The dynamic change in the overall detachment rate of spherical biofilms in a biofilm airlift suspension reactor was measured after a downshift of the substrate loading rate to zero while all other conditions remained constant. In contrast to the expectations, the overall detachment rate decreased rapidly to a nearly stable level. Correlations available from literature were not able to describe this phenomenon. Concepts were formulated which can describe the observations from this study. Research under dynamic conditions and careful monitoring of the biofilm surface area and biofilm morphology are necessary to elucidate and discriminate biofilm detachment mechanisms. (c) 1995 John Wiley & Sons, Inc. 相似文献
993.
Detachment of biomass from suspended nongrowing spherical biofilms in airlift reactors 总被引:2,自引:0,他引:2
Gjaltema A Tijhuis L van Loosdrecht MC Heijnen JJ 《Biotechnology and bioengineering》1995,46(3):258-269
In three-phase internal loop airlift reactors, the detachment of biomass from suspended biofilm pellets in the presence of bare carrier particles was investigated under nongrowth conditions. The detachment rate was dominated by collisions between bare carrier particles and biofilm pellets. The concentration of bare carrier particles and the carrier roughness strongly influenced the detachment rate. A change in flow regime from bubbling to slug flow considerably increased the detachment rate. Otherwise, the superficial gas velocity did not directly affect the detachment rate. The influence of particle size was not clear. The bottom clearance did not affect the detachment rate within the tested range. Other aspects of reactor geometry might be important. The main detachment processes were abrasion and breakage of biofilm pellets. During the detachment process, two phases could be distinguished. In the first phase the detachment was relatively high, and both breakage and abrasion of biofilm pellets occurred. During the second phase, breakage dominated and the detachment rate was lower. The two-phase behavior is explained by differences in strength between the inner and outer biofilm layers, possibly caused by variations in local growth rates during biofilm formation. Differences in growth history might also explain the various detachment rates observed with different biofilm batches. (c) 1995 John Wiley & Sons, Inc. 相似文献
994.
With glucose-limited continuous cultures of Petunia hybrida six steady states were obtained at specific growth rates varying from 0.0035 to 0.012 h(-1) (corresponding with culture residence times varying from 285 to 85 h). The macromolecular and the elemental biomass composition which were determined in four steady states showed no major differences over the range of growth rates examined. During all six steady states specific subtrate and oxygen consumption as well as biomass and extracellular product formation rates were monitored. Moreover the specific activities of the mitochondrial cytochrome and alternative pathway were determined and used to estimate specific adenosine triphosphate (ATP) production rates. Data thus obtained were used in the determination of maintenance and true growth yield parameters. For the maintenance on glucose and ATP values of 0.0070 C-mol/C-mol/h and 0.034 mol/C-mol/h were obtained, respectively. True yields of biomass on glucose and ATP were 0.50 C-mol/C-mol and 0.28 C-mol/mol, respectively. (c) 1995 John Wiley & Sons, Inc. 相似文献
995.
One of the critical factors limiting the development of membrane systems for protein fractionation has been the poor selectivity that has generally been obtained with these membrane devices. We have demonstrated that it is possible to dramatically improve the selectivity of available membrane systems by exploiting the different electrostatic interactions between the two proteins and the membrane. The separation factor for the albumin-hemoglobin system could be increased to more than 70 simply by reducing the salt concentration and adjusting the pH to around 7 (near the isoelectric point of hemoglobin). This very high selectivity was a direct result of the strong electrostatic exclusion of the charged albumin from the membrane pores under these conditions. This high selectivity makes it possible to very effectively separate these albumin-hemoglobin mixtures using membrane filtration, and this was demonstrated experimentally using both a simple batch filtration process and a continuous diafiltration system. The hemoglobin recovery in the diafiltration experiment was greater than 70% after a 3-diavolume filtration, with the Hb purification factor being around 100 under these conditions. These results clearly demonstrate the potential of membrane systems for the fractionation of proteins even with very similar molecular weights. (c) 1995 John Wiley & Sons, Inc. 相似文献
996.
Henk van der Werff 《Brittonia》1995,47(4):372-375
Aiouea opaca andBeilschmiedia hexanthera, recently collected in central French Guiana, are described and illustrated. 相似文献
997.
Expression of insulin-like growth factor II (IGF-II) and histological changes in the thymus and spleen of transgenic mice overexpressing IGF-II 总被引:2,自引:0,他引:2
Leo T. M. Van der Ven Paul J. M. Roholl Maria G. Reijnen-Gresnigt Ruud J. Bloemen Sylvia C. van Buul-Offers 《Histochemistry and cell biology》1997,107(3):193-203
Previously, transgenic mice were constructed overexpressing human insulin-like growth factor II (IGF-II) under control of
the H2kb promoter. The IGF-II transgene was highly expressed in thymus and spleen, and these organs showed an increase in weight. In
the current study we have analyzed the sites of IGF-II mRNA expression, the distribution of IGF-II, IGF-I, and both IGF receptors,
and histomorphometrical changes in thymus and spleen. With in situ mRNA hybridization, expression of the IGF-II transgene
is found with high intensity in the thymic medulla and in the white pulp/marginal zone of the spleen, whereas there were scattered
positive cells in the thymic cortex and in the splenic red pulp. Hybridization was restricted to non-lymphocytic cells. Immunohistochemistry
revealed intense IGF-II peptide staining with the same distribution as IGF-II mRNA. There was additional intense IGF-II staining
of all elements in the splenic red pulp (including trabeculae) and diffuse, low level staining in the thymic cortex. These
findings were not observed in control mice. In the thymic medulla, most IGF-II producing cells co-labelled with keratin, whereas
a minor population also stained for the monocyte/macrophage marker MOMA-2. In the spleen, co-labelling of IGF-II producing
cells was found with MOMA-1 (marginal zone), or with the dendritic cell marker NLDC-145 (red pulp). IGF-I and both IGF receptors
were found in these organs in nearly all cell types, with a similar pattern in transgenic mice and in control animals. Histomorphometric
analysis revealed a marked increase of thymus cortex size and an increased trabecular size in the spleen. This suggests that
IGF-II overproduction induces local effects (auto/paracrine) in the thymic cortex, but not in the thymic medulla. Trabecular
growth in the spleen most likely is a distant effect (paracrine or endocrine) of IGF-II overproduction.
Accepted: 5 September 1996 相似文献
998.
999.
Hashem F.M. Saleh S.A. Berkum P. van Voll M. 《World journal of microbiology & biotechnology》1997,13(3):335-340
Survival and viability of Bradyrhizobium inoculant on fungicide-treated peanut seed and the resulting effects on nitrogen fixation, plant growth and seed yield were determined. Vitavax and Benomyl had the most and least lethal actions against Bradyrhizobium strains grown on YEM medium containing a fungicide, respectively, while Thiram and Captan effects were intermediate. Survival of Bradyrhizobium USDA 3384 and USDA 3456, as single strain peat inoculants, on peanut (Arachis hypogaea L. var. Florunner) seeds treated with Benomyl or Vitavax at the rate of 3g/kg seed was also examined. Both fungicides inhibited the growth and affected the survival of strain USDA 3384 on peanut seed. Vitavax killed the inoculant in 9 h. In contrast, USDA 3456 resisted both fungicides, and survived for up to 72h. Nodule formation on greenhouse-grown plants inoculated with USDA 3384 was inhibited by all fungicides. Shoot dry weight and plant nitrogen content significantly decreased as compared to controls. Fungicides, except Vitavax, had a slight effect on nodulation and plant growth when USDA 3456 was used as inoculant. The agronomic importance of fungicide-inoculant interaction was examined in field experiments conducted in Egypt in soil free of peanut-nodulating Bradyrhizobium, where seeds were treated with a combination of two fungicides and a single strain peat inoculant of either USDA 3384 or USDA 3456. All fungicides decreased nodulation, nitrogen fixation, plant growth and seed yield, especially with USDA 3384 as inoculant. Fungicides inhibited viability and survival of Bradyrhizobium on peanut seeds which decreased nodule formation leading to reduced peanut seed yield. 相似文献
1000.