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71.
Dissociation of influenza virus hemagglutinin and neuraminidase eliminates their intravirionic antigenic competition. 总被引:5,自引:2,他引:3
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When presented together on the intact influenza virus particle, the external hemagglutinin (HA) and neuraminidase (NA) antigens are competitive, with HA dominant over NA in both T- and B-cell priming (B. E. Johansson, T. M. Moran, and E. D. Kilbourne, Proc. Natl. Acad. Sci. USA 84:6869-6873, 1987). Dissociation and purification of HA and NA from virus and their injection separately or in combination into BALB/c mice eliminates their antigenic competition as measured by antibody response, confirming that it is their structural association that leads to what we have termed intravirionic antigenic competition. We discuss this phenomenon with respect to previously described intermolecular antigenic competition and with regard to its probable mechanism. Our findings are relevant to contemporary interest in viral vaccine vectors and multicomponent vaccines. 相似文献
72.
Enterally administered, heme is a good source of iron in humans and other animals, but the metabolism of heme by enterocytes has not been fully characterized. Caco-2 cells in culture provide a useful model for studying cells that resemble small intestinal epithelium, both morphologically and functionally. In this paper we show that heme oxygenase, the rate-controlling enzyme of heme catabolism, is present in abundance in Caco-2 cells, and that levels of its mRNA and activity can be increased by exposure of the cells to heme or metal ions (cadmium, cobalt). Caco-2 cells also contain biliverdin reductase activity which, in the basal state, is similar to that of heme oxygenase (approximately 40 pmole of product per mg protein per minute); however, when heme oxygenase is induced, biliverdin reductase may become rate-limiting for bilirubin production.Abbreviations BVR
biliverdin reductase
- DMEM
Dulbecco's modified Eagles medium
- DMSO
dimethyl sulfoxide
- HO
heme oxygenase
- 1xSSC
a solution of 0.015 M sodium citrate/0.15 sodium chloride 相似文献
73.
Restriction site mapping of chloroplast DNA from 31 species representing 26 genera of theRanunculaceae was performed using eleven restriction endonucleases. The chloroplast genome varies in length from approximately 152 to 160 kb. Length variants are frequent in theRanunculaceae and range from usually less than 300 bp to rarely 1.5 kb. The inverted repeat is extended into the large single copy (LSC) region by 4–4.5 kb inAnemone, Clematis, Clematopsis, Hepatica, Knowltonia, andPulsatilla. Several inversions are present in the LSC-region of the cpDNA in all these genera and inAdonis. The frequency of restriction site mutations varies within the chloroplast genome in theRanunculaceae between 4 and 32 mutations per kilobase, and is lowest in the inverted repeat and the regions containing the ATPase-genes and the genespsaA, psaB, psbA, rpoB, andrbcL. A total of 547 phylogenetically informative restriction sites was utilized in cladistic analyses of the family using Wagner, Dollo, and weighted parsimony. These three parsimony analyses result in different tree topologies. Four, six, and one equally most parsimonious trees were obtained with Wagner, Dollo, and weighted parsimony, respectively. The amount of support for the monophyletic groups was evaluated using bootstrapping and decay analysis. All three parsimony methods suggest thatHydrastis is the sister group to the remainder of theRanunculaceae, and that theAnemone-Clematis group, which shares several derived cpDNA rearrangements, is monophyletic. Only a few of the traditional groups in theRanunculaceae are supported by cpDNA restriction side data. Only Dollo parsimony provides support for the hypothesis thatThalictroideae andRanunculoideae are monophyletic. 相似文献
74.
Mats E. Johansson 《植被学杂志》1993,4(5):621-632
Abstract. Two marginal and two central populations of the pseudo-annual aquatic plant Ranunculus lingua were studied over four years. The main purpose was to quantify potentially influential abiotic and biotic factors and to derive predictions about life-history differences between the populations. Variation in abundance and height of R. lingua ramets at different depths were related to water-level fluctuations, to abundance of other helophyes (emergent macrophytes), and to the occurrence of invertebrate grazing and fungal pathogens. Clear differences between marginal and central populations were shown in the depth distribution of ramet numbers and ramet heights, as well as in the dynamic patterns, where marginal populations had a higher flux of ramets. These patterns and regression analyses indicated that abiotic factors have a greater influence in marginal populations, whereas biotic factors are more important in central populations. It is suggested that marginal habitats for R. lingua would favour life-histories with a high reproductive capacity, whereas a large size of ramet would be the most important life-history feature in central habitats. This was supported by the fact that ramets in marginal populations, in spite of their smaller size, produced higher number of rhizomes than ramets in central populations. Variation in regional abundance was finally related to differences in demographic processes and dispersal potential between the populations. 相似文献
75.
Berit Backlund Hk Anette M. Johansson Stephan Hjorth Staffan Sundell Uli Hacksell 《Chirality》1993,5(3):112-119
Racemic 5-methoxy-2-methyl-2-dipropylaminotetralin ( 3 ) has been prepared by a short synthetic route, in which the N,N-dipropyliminium perchlorate of 5-methoxy-2-tetralone ( 4 ) is a key intermediate. Racemic 3 was resolved by crystallization of the corresponding diastereomeric di-p-toluoyltartrates. The enantiomeric excess (%ee) of the phenolic derivatives of (+)-(R)- and (?)-(S)-3 [(+)-(R)- and (?)-(S)-2] was determined by 1HNMR spectroscopic analysis of the corresponding diastereomeric (?)-(R)-1,1′-binaphthyl-2,2′-diylphosphoric acid salts utilizing 13C satellites. X-ray crystallography established the absolute configuration of (?)-(S)-2 · HCl. The enantiomers of 2 were tested for hippocampal output of 5-hydroxytryptamine, 5-hydroxyindoleacetic acid, and dihydroxyphenylacetic acid in rats by use of in vivo microdialysis. The (?)-(S)-enantiomer appeared to affect 5-HT-turnover, whereas (+)-(R)- 2 was inactive. Results obtained provide support for the previously reported hypothesis that the inactivity of (?)-(S)- 2 at central DA receptors is caused by the steric bulk of the C(2)-methyl group. This makes it possible to define a “DA D2 receptor essential volume.” © 1993 Wiley-Liss, Inc. 相似文献
76.
Polylysine has been covalently bound to human transferrin in a 1:1 molar ratio over a disulfide bond that can be easily split by reducing agents such as dithiothreitol. The association constant for the binding of the transferrin-polylysine derivative to transferrin receptors present on rat erythroblasts and the number of binding sites were identical to the corresponding values found for native transferrin. The incubation of the cells with transferrin-polylysine affected the partitioning of erythroblasts in a charge-sensitive aqueous two-phase system containing Dextran and polyethylene glycol. The polylysine part introduced a nonspecific influence on the partitioning that could be eliminated by preincubation of the cells with an excess of sialic acid. The partition ratio, G, of the erythroblasts changed with a factor of 1.9 for each set of 100,000 polylysine chains attached per cell. 相似文献
77.
An increasing population of the mute swan Cygnus olor , was studied from its very establishment in 1976 until 1998. As the number of pairs increased, there was a decline in all production parameters, including the average number of clutches per pair, the average number of broods per clutch, and the average number of fledged young per brood. In a multiple regression analysis covering the whole breeding season, the number of pairs and the average number of clutches per pair explained 71% of the variation in the average number of fledglings per pair. During the brood season, the average number of fledglings per brood was an additionally important parameter in explaining fledgling production. Habitat quality seemed to affect breeding: in places occupied earlier more cygnets fledged from a clutch than in habitats inhabited later. The decreased production of young very likely reflects density-dependent effects on reproduction. This density dependence seems to operate on the breeding grounds, since winter harshness did not affect breeding success. Density-dependent processes started acting already when pairs were beginning to nest, and continued during the brood period. Density dependence has apparently not been detected at the pair stage in earlier studies of bird populations. 相似文献
78.
Min Lu Per- Ake Albertsson G te Johansson Folke Tjerneld 《Journal of chromatography. B, Analytical technologies in the biomedical and life sciences》1996,680(1-2):65-70
Benzoyl dextran with a degree of substitution of 0.18 was synthesized by reacting dextran T500 with benzoyl chloride. A new type of aqueous two-phase system composed of benzoyl dextran as bottom phase polymer and the random copolymer of ethylene oxide and propylene oxide (Ucon 50-HB-5100) as top phase polymer has been formed. The phase diagram for the system Ucon 50-HB-5100-benzoyl dextran with a degree of substitution of 0.18 was determined at room temperature. This two-phase system has been used to purify 3-phosphoglycerate kinase from bakers' yeast. The top-phase polymer (Ucon) can be separated from target enzyme by increasing the temperature. The bottom-phase polymer (benzyol dextran) could be recovered by addition of salt. Yeast homogenate was partitioned in a primary Ucon 50-HB-5100-benzoyl dextran aqueous two-phase system. After phase separation the top phase was removed and temperature-induced phase separation was used for formation of a water phase and a Ucon-rich phase. The benzoyl dextran-enriched bottom phase from the primary system was diluted, and the polymer was separated from water by addition of Na2SO4. 相似文献
79.
80.
The bat fauna of 35 islands in a large lake in central Sweden were examined using ultrasound detectors. We tested the hypothesis that there is no difference in species number between the mainland and the island fauna. Eight species were found. Species numbers were analysed against island area, area of some habitats (coniferous forest, deciduous forest, semi-open habitats and open habitats), degree of isolation (distance from mainland and from stepping stones) and time spent searching for bats. Species number increased with area of deciduous forest. Presence of houses tended to increase species number. There seems to be a negative relationship between species number and degree of isolation (nearly significant). The results suggest that at least three species, Myotis brandti (Eversmann, 1845), M. mystacinus (Kuhl, 1819) and Plecotus auritus (Linnaeus, 1758), are negatively affected by forest patchiness. These species occurred mainly on large islands. Thus, the results do not support the hypothesis. The reasons why some species avoid open habitats are discussed. 相似文献