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941.
Synthesis of lysogangliosides 总被引:6,自引:0,他引:6
The synthesis of gangliosides GM3, GM2, GM1, and GD1a solely lacking the fatty acid moiety, and thus called lysogangliosides in analogy to lysophospholipids, is described. Since a selective elimination of the fatty acid residue has not been achieved as yet, the gangliosides were first subjected to alkaline hydrolysis. By this procedure the fatty acyl as well as the acetyl groups of the sialic acid residue(s) were completely removed. The acetamido group of the N-acetylgalactosamine moiety of the gangliosides GM2, GM1, and GD1a was very little (congruent to 10%) hydrolyzed. In a two-phase system composed of water and ether, the selective protection of the sphingoid amino group was accomplished with a hydrophobic protective group (9-fluorenylmethoxycarbonyl). Lysogangliosides were obtained after re-N-acetylation of the sialooligosaccharide amino group(s) followed by removal of the protecting group. The overall yield was about 30%. The structures of the lysogangliosides were confirmed by chemical analysis as well as negative ion FAB mass spectrometry and 1H NMR spectroscopy. By simple re-N-acylation of lysogangliosides with any labeled fatty acid, labeled gangliosides are now obtainable that are identical with their parent gangliosides except for their labeled fatty acid residue. This has been demonstrated by the synthesis of GM1 with a [1-13C]palmitic acid moiety in its ceramide portion. If desired, double-labeled gangliosides may be obtained by use of labeled acetic anhydride in the synthesis of the lysogangliosides. 相似文献
942.
E Gomard Y Hénin G Sterkers M Masset R Fauchet J P Lévy 《Journal of immunology (Baltimore, Md. : 1950)》1986,136(11):3961-3967
The clone TA10 is a T3+ T4+ T8- proliferative and cytolytic human T cell clone. This clone has been shown to be specific for the hemagglutinin of influenza A Texas virus and restricted by an HLA class II molecule associated with the DRw8-Dw8.1 phenotype. Here we show that TA10 and all of its subclones can also react with eight HLA-DRw8 negative, Epstein-Barr virus (EBV)-transformed cell lines or phytohemagglutinin blasts in the absence of influenza antigens. All of these cell lines are HLA-DR2/DR4 with a classic DR2 long haplotype. The only nonreactive HLA-DR2/DR4 cell line observed bears a DR2 short haplotype. Only heterozygous HLA-DR2/DR4 but not parental DR2 or DR4 EBV-transformed cell lines can be recognized by TA10, indicating that the cross-reacting determinant is a transcomplementation product between HLA-DR2 and HLA-DR4 haplotypes. DR-specific, but not DQ- or DP-specific monoclonal antibodies, inhibit in the proliferation assay and in the chromium release test both the DRw8-Dw8.1-restricted and the anti-DR2/DR4 reactions. These results show that HLA-DR-restricted, anti-viral human T cell clone can evidence cross-reactivity for allospecific class II molecules of the major histocompatibility complex, and human CTL can recognize transcomplementation products of class II HLA genes. In addition, the results suggest that a beta-chain coded for by an HLA-DR gene and associated with an alpha-chain coded for by a still unidentified but possibly HLA-DQ gene constitute this functional transcomplementation product. 相似文献
943.
944.
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946.
Summary Spontaneous cell-to-cell transformation between naturally competent bacteria on selective media resulted in an overestimation of the transferability of genetic information. EDTA effectively prevented transformation on selective media whereas DNaseI did not reliably inhibit cell-to-cell transformation. An improved method to estimate gene transfer frequencies is described. 相似文献
947.
At least two types of glucose transporter exist in cultured renal epithelial cells, a Na(+)-glucose cotransporter (SGLT), capable of interacting with D-glucose but not 2-deoxy-D-glucose (2dglc) and a facilitated transporter (GLUT) capable of interacting with both D-glucose and 2dglc. In order to examine the polarity of transport in cultured renal epithelia, 2dglc and D-glucose uptakes were measured in confluent cultures of LLC-PK1 cells grown on collagen-coated filters that permitted access of medium to both sides of the monolayer. The rates of basolateral uptake of both 1 mM glucose (Km 3.6 mM) and 1 mM 2dglc (Km 1.5 mM) were greater than apical uptake rates and the (apical-to-basolateral)/(basolateral-to-apical) flux ratio was high for glucose (9.4) and low for 2dglc (0.8), thus, confirming the lack of interaction of 2dglc with the apical SGLT. Specific glucose transport inhibitor studies using phlorizin, phloretin and cytochalasin B confirmed the polarised distribution of SGLT and GLUT in LLC-PK1 cells. Basolateral sugar uptake could be altered by addition of insulin (1 mU/ml) which increased 2dglc uptake by 72% and glucose uptake by 50% and by addition of 20 mM glucose to the medium during cell culture which decreased 2dglc uptake capacity at confluence by 30%. During growth to confluence, 2dglc uptake increased to a maximum, then decreased at the time of confluence, coincident with a rise in uptake capacity for alpha-methyl-D-glucoside, a hexose that interacts only with the apical SGLT. It was concluded that the non-metabolisable sugar 2dglc was a useful, specific probe for GLUT in LLC-PK1 cells and that GLUT was localised at the basolateral membrane after confluence. 相似文献
948.
Christelle Hély Kelly K. Caylor Peter Dowty Samuel Alleaume Robert J. Swap Hank H. Shugart Christopher O. Justice 《Ecosystems》2007,10(7):1116-1132
Abstract
We present a regional fuel load model (1 km2 spatial resolution) applied in the southern African savanna region. The model is based on a patch-scale production efficiency
model (PEM) scaled up to the regional level using empirical relationships between patch-scale behavior and multi-source remote
sensing data (spatio-temporal variability of vegetation and climatic variables). The model requires the spatial distribution
of woody vegetation cover, which is used to determine separate respiration rates for tree and grass. Net primary production,
grass and tree leaf death, and herbivory are also taken into account in this mechanistic modeling approach. The fuel load
model has been calibrated and validated from independent measurements taken from savanna vegetation in Africa southward from
the equator. A sensitivity analysis on the effect of climate variables (incoming radiation, air temperature, and precipitation)
has been conducted to demonstrate the strong role that water availability has in determining productivity and subsequent fuel
load over the southern African region. The model performance has been tested in four different areas representative of a regional
increasing rainfall gradient—Etosha National Park, Namibia, Mongu and Kasama, Zambia, as well as in Kruger National Park,
South Africa. Within each area, we analyze model output from three different magnitudes of canopy coverage (<5, 30, and 50%).
We find that fuel load ranges predicted by the model are globally in agreement with field measurements for the same year.
High rainfall sustains green herbaceous production late in the dry season and delays tree leaf litter production. Effect of
water on production varies across the rainfall gradient with delayed start of green material production in more arid regions. 相似文献
949.
N A Medvedeva T C Vo I Iu Sergeev I M Rodionov 《Biulleten' eksperimental'no? biologii i meditsiny》1987,103(5):517-520
Neuromediated behaviour of feline caudal femoral arteries was studied in vitro. Transmural stimulation of arteries, previously constricted by noradrenaline, caused an up to 58% relaxation of the induced tone. Atropine (10(-5) g/ml) blocked this response by 93%. The removal of endothelium did not affect the magnitude of the response. It is suggested that the caudal femoral artery is an example of a blood vessel which has muscarinic receptors located directly on its smooth muscles. 相似文献
950.
Isoforms of myosin and actin in human, monkey and rat myometrium. Comparison of pregnant and non-pregnant uterus proteins 总被引:1,自引:0,他引:1
Using several electrophoretic procedures, we have compared the forms of myosin and actin in pregnant and non-pregnant uterus of woman, monkey (Macaca fascicularis) and rat. On non-dissociating gels, native myosin of the three species migrates as a single band, of identical mobility independently of the physiological state. Remigration of this band in dissociating conditions shows that it is constituted of two heavy chains of respectively 201 kDa and 205 kDa; the relative proportions of these two bands are different for the three animal species but do not vary during pregnancy. Using two-dimensional gel electrophoresis, we found that the 17-kDa light chain of purified uterus myosin exists under two isoelectric forms, the more acidic one becoming progressively predominant at the end of pregnancy in the human as in the monkey uterus, while we observed no changes in the rat. In two-dimensional gel electrophoresis, actin of human, monkey and rat uterus is present under three isoforms, the most basic one (the gamma form) increasing early in pregnancy in the two primate species but being always the most abundant form in the rat. The ATPase activity of human uterus myosin was found to be similar for the protein extracted from both pregnant and non-pregnant uterus. The changes observed in the 17-kDa light chain and in the actin isoforms might nevertheless participate in the modifications of contractility of the uterus during pregnancy of the primates. 相似文献