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21.
The 13C-n.m.r. spectra of asialo-GM1 and GM1-oligosaccharide are completely assigned and compared to those previously found for intact GM1 and for the series GM4, GM3, GM2, GM1, GD1a, GD1b, and GT1b. Removal of the ceramide residue from GM1 liberated a free, reducing aldehyde group, which was reflected in a doubling of the 13C-n.m.r. signals assignable to the d-glucose residue because of α,β equilibrium. The spectrum of asialo-GM1 lacks the resonances from the sialic acid residue, as expected; in addition, several resonances from the neutral gangliotetraglycosyl residue shifted to different field positions after removal of sialic acid from GM1. These resonances include that of C-4 of the inner β-d-galactosyl residue, and C-1 of the 2-acetamido-2-deoxy-d-galactosyl residue that is near the site of attachment of the sialosyl residue. The differences between the chemical shifts of the carbon resonances of oligomeric and monomeric saccharides, termed linkage shifts, provide a quantitative assignment aid. They are ~ of those for residues linked to sialic acid than those for residues linked to the neutral hexose chain. Correlations among linkage shifts for pairs of glycosidically-linked carbon atoms for asialo-GM1 and GM1-oligosaccharide were compared with those for the series of gangliosides GM4 to GT1b, and differences are noted for resonances for carbon atoms near the sialic acid residue. The spectrum of ganglioside GM1b, a positional isomer of GM1 whose 13C-n.m.r. spectrum has not yet been observed, is predicted. 相似文献
22.
Loss and resynthesis of a developmentally regulated membrane protein (gp80) during dedifferentiation and redifferentiation in Dictyostelium 总被引:1,自引:0,他引:1
When developing cultures of Dictyostelium discoideum are disaggregated and resuspended in nutrient medium, they lose the capacity to rapidly reaggregate after 90 min, in a rapid and synchronous step referred to as the "erasure event." They then proceed to lose remaining developmentally acquired functions in a program of dedifferentiation culuminating with the loss of EDTA-resistant cohesion roughly 5 hr later. Immediately following the erasure event, cells can be stimulated to reenter the developmental program even though they still possess a number of developmentally acquired functions. These cells therefore appear to undergo dedifferentiation and redifferentiation simultaneously (D. R. Soll and L. H. Mitchell, 1982, Dev. Biol. 91, 183-190). In this report, we have employed an antiserum made against a developmentally acquired membrane glycoprotein, gp80, to examine whether gp80 is lost during dedifferentiation and whether it is either reutilized or resynthesized during redifferentiation. Results are presented which demonstrate that (1) when 9-hr developing cells are disaggregated and resuspended in nutrient medium, gp80 continues to accumulate for several hours after the erasure event, then is lost at roughly the same time as EDTA-resistant cohesion; (2) when cells are stimulated to reenter the developmental program immediately after the erasure event, both gp80 and EDTA-resistant cohesion are still lost according to the program of dedifferentiation, but are then reacquired soon afterwards according to the program of redifferentiation; (3) during redifferentiation, cells do not reutilize gp80 which had been synthesized during initial development; rather they synthesize gp80 de novo; and (4) developing cells of a dedifferentiation-defective variant, HI4, when disaggregated and resuspended in nutrient medium, retain gp80, EDTA-resistant cohesion, and the capacity to rapidly reinitiate aggregation for at least 12 hr. This last result indicates that the loss of gp80 is regulated by the dedifferentiation process and is not an independent response to disaggregation or the reintroduction of nutrients. Together, these results reinforce the conclusion that dedifferentiation and redifferentiation can function independently and simultaneously in the same cells. 相似文献
23.
ARTHUR G. HUMES 《Zoological Journal of the Linnean Society》1996,118(1):59-82
Three new monotypic genera of copepods (Poecilostomatoida) are associated with the hermatypic shallow-water coral Psammocora (Stephanaria) logianensis near Noumea, New Caledonia: in the Anchimolgidae, Lipochaetes extrusus (antenna 4-segmented, endopods absent in legs 3 and 4) and Dumbeana undulatipes (antenna 3-segmcntcd, endopod of leg 3 with formula 0 1; 0–2; 1,11,2; leg 4 endopod with 0 1:1); and in the Rhynchomolgidae; Emunoa proknta (leg 4 endopod with 0 1;II, antenna 4-segmented, mandible witli outer pointed process and inner row of spines). Copepoda (primarily Poecilostomatoida and Siphonostomatoida, but also relatively few Cyclopoida and Harpacticoida) are very frequent associates or parasites of Scleractinia. At present 245 species from 48 scleractinian coral genera are known. Species of these copepod associates, their host genera, and localities, described since (and those not included in) previous publications of the author are listed. 相似文献
24.
In many German forest soils low base saturation of CEC in deeper soil layers was reported and acidic deposition is seen as
the major cause of these findings. To test this hypothesis we sampled 5 New Zealand forest soils from pristine beech (Nothofagus fusca, N. menziesii, N. solandri) sites under climatic and geological conditions comparable to higher elevations in Germany. The soils developed from granite
and greywacke. Soil samples were analyzed for pH and the exchangeable cations were extracted with 1M NH4Cl. The base saturation of all soil profiles was very low, even in deeper layers and was thus similar to the patterns found
in many German forest soils. The pH was generally higher in the New Zealand soils as compared to Germany. The reason for the
depletion of base cations in deeper soil layers of New Zealand forest soils is most likely the leaching of base cations with
HCO3
- resulting from the dissociation of carbonic acid in connection with high amounts of seepage. Thus, under high rainfall conditions,
the low base saturation found in deeper layers of forest soils cannot exclusively be attributed to the effects of acidic depositions
and land use. ei]Section editor: R F Huettl 相似文献
25.
The paper describes the local, national, European and wider-area framework, statutes, and formal and voluntary mechanisms for managing European estuaries. These aspects are discussed in relation to two large and representative estuarine systems, the Tagus, Portugal, and the Humber, on the English North Sea coast As estuaries are sites of many activities and uses, most of which are encouraged or at least condoned, management has the role of preventing and resolving conflicts between those uses and users. Accepted uses of estuaries include the discharge and dumping of waste materials, fin and shell-fisheries, conservation, land reclamation, natural usage, abstraction by industry, and recreation. Estuarine management is now being carried out within the constraints of local and regional government planning, planning and activities of water pollution control bodies, fisheries control bodies, and navigation and port authorities The Tagus and Humber estuaries support all of the above activities and uses, and have controls within a European legislative framework but have differing histories of management and planning in order to resolve conflicts. In addition the Humber is subject to controls placed on North Sea areas. The paper discusses the relevant national and European legislation (Directives) and accepted practices for management. Furthermore, the paper discusses the formulation and practice of estuarine management plans as used by various bodies (nature conservation, water quality and regional authority). It is of particular note that the lessons from these two estuaries are relevant to many other European estuaries. 相似文献
26.
27.
中国紫金牛属一新种 总被引:1,自引:1,他引:0
胡启明 《热带亚热带植物学报》1995,3(4):13-16
中国紫金牛属一新种胡启明(中国科学院华南植物研究所,广州510650)关键词紫金牛属;光萼紫金牛;新种ANEWSPECIESOFARDISIAFROMCHINA¥HuChiming(SouthChinaInstituteofBotany,Academ... 相似文献
28.
The distribution of the New Zealand flatworm (Artioposthia triangulata) in Scotland was surveyed between July 1991 and February 1993. There were 348 records from domestic gardens, 56 from botanic gardens, garden centres and nurseries, with only 13 from farms. Although most of the records came from around the major cities the flatworm was found to have become established throughout the Scottish mainland and some of the Islands, e.g. Bute, Gigha, Orkney and Skye. The impact of the flatworm on earthworm populations in agricultural land in Scotland was, as yet, found to be minimal but the fact that seven adjacent farms near Dunoon were infected suggested it could be spread from farm to farm and that in the West of Scotland it could become widespread in agricultural land. 相似文献
29.
Three new species of Tropodiaptomus from southern Africa are described, Tropodiaptomus zambeziensis, T. bhangazii, and T. capriviensis. Type localities are a rice paddy on the Zambezi river delta, a coastal lake in Zululand, and temporary pools in Bushmanland and the eastern Caprivi in Namibia. Speciation of Tropodiaptomus in the warm inland waters of southern Africa is much more extensive than was formerly realised. 相似文献
30.
武陵山地区鱼类寄生杆咽属线虫两新种 总被引:1,自引:0,他引:1
本文报道在武陵山地区的白甲鱼[(Varicorkinus(Onychostoma)simus(SauvageetDabry)]和沪溪直口峻(RectorisluxiensisWuetYao)中发现的两种杆咽属(Rhabdochona)线虫新种,定名为白甲鱼杆咽线虫,新种(RhabdOchonaonyrkostomisp.nov.)和短咽杆咽线虫,新种(RhabdOchonabrevichonasp.nov.),并对两新种进行了测量和详细的描述。 相似文献