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2.
Migration of O-acetyl groups in N,O-acetylneuraminic acids 总被引:6,自引:0,他引:6
J P Kamerling R Schauer A K Shukla S Stoll H Van Halbeek J F Vliegenthart 《European journal of biochemistry》1987,162(3):601-607
Highly purified N-acetyl-4-O-acetylneuraminic acid (Neu4,5Ac2), N-acetyl-7-O-acetylneuraminic acid (Neu5,7Ac2) and N-acetyl-7,9-di-O-acetylneuraminic acid (Neu5,7,9Ac3) were used to study spontaneous migrations of acetyl groups between hydroxyl groups. The techniques applied involved thin-layer chromatography, gas-liquid chromatography/mass spectrometry, high-performance liquid chromatography and 360-MHz 1H-NMR spectroscopy. It was found that at pH values at which no significant de-O-acetylation is observed: (a) Neu5,7Ac2 can easily be transformed into Neu5,9Ac2, (b) Neu5,7,9Ac3 yields an equilibrium of Neu5,7,9Ac3 and Neu5,8,9Ac3 in a molar ratio of approximately 1:1, and (c) Neu4,5Ac2 does not give rise to O-acetyl migrations. The importance of these findings is discussed in terms of the biosynthesis of O-acetylated sialic acids. 相似文献
3.
The cell-bound sialidase of Actinomyces viscosus DSM 43798 was solubilized by mechanical cell disruption and lysozyme treatment. The enzyme was enriched 30,000-fold by cation-exchange chromatography, gel-filtration, and FPLC ion-exchange chromatography, thus obtaining 10 micrograms sialidase protein from 26 g wet cells with a specific activity of 680 U/mg protein. Since sialidase activity was also found in the culture medium, this enzyme was isolated as well, requiring the additional application of FPLC gel-filtration. Both sialidase preparations were apparently homogenous on SDS-PAGE and have similar properties. The substrate specificity of the A. viscosus sialidase was tested with 16 sialoglycoconjugates: The enzyme showed a higher activity with serum glycoproteins than with gangliosides, mucins or sialyllactoses. 4-O-Acetylated N-acetylneuraminic acid was not cleaved from equine submandibular gland mucins or serum glycoproteins in contrast to N-acetyl- and N-glycoloylneuraminic acid. 9-O-Acetyl-N-acetylneuraminic acid was released from bovine submandibular gland mucin, as confirmed by TLC. The sialidase hydrolyses alpha(2----6)-linkages more rapidly than alpha(2----8)- and alpha(2----3)-bonds. Cations, except Hg2+, or chelating agents have no influence on enzyme activity. The sialidase has a relatively high molecular mass of 150 kDa, but consists of only one unit. The enzyme is labile towards freezing and thawing, but can be stored at 4 degrees C in 0.1 M acetate buffer, pH 5. 相似文献
4.
CMP-Neu5Gc has been shown to be transported into mouse liver Golgi vesicles by a specific carrier the characteristics of which were investigated in detail. In the system employed, CMP-Neu5Gc enters the Golgi vesicles within 2 min; transport was saturable with high concentrations of the sugar-nucleotide and was dependent on temperature. A kinetic analysis gave an apparent Km of 1.3 μM and a maximal transport velocity of 335 pmol/mg protein per min. Almost identical values were obtained with CMP-Neu5Ac, under the same incubation conditions. Furthermore, the uptake of CMP-Neu5Gc was inhibited by CMP-Neu5Ac, a substrate analogue. Conversely, the uptake of CMP-Neu5Ac was inhibited by CMP-Neu5Gc to the same extent, leading to the conclusion that the transport of CMP-Neu5Ac and CMP-Neu5Gc is mediated by the same carrier molecule. This transport system for CMP-Neu5Gc involves both CMP and CMP-Neu5Gc since intravesicular CMP induced the entry of external CMP-Neu5Gc. 相似文献
5.
Hans Fricke Karen Hissmann Jürgen Schauer Olaf Reinicke Lutz Kasang Raphael Plante 《Environmental Biology of Fishes》1991,32(1-4):287-300
Synopsis In 1987 and 1989 coelacanths were observed for the first time in their natural habitat with the help of submersibles. Coelacanths were found between 150–253 m depth, their preferential depth seems to be around 200 m; the water temperature ranged between 16.5–22.8° C. During the day coelacanths aggregate in small non-aggressive groups in sheltered lava-caves. Caves might be a limiting factor for distribution. At night they leave the caves for hunting by drifting singly along the steep lava slopes. They migrate between different caves located within a large home range covering more than 8 km coastline. Coelacanths are site-attached, some for a period of at least 2 years. Our own observations and earlier catch records show that only the west coast of Grand Comoro is a suitable coelacanth habitat with more structural complexity and prey fish abundance than other coastlines of the island. From our survey we estimated a total coelacanth population off Grand Comoro to be 150–210 individuals; a saturated population would be 370–510 individuals. This small relict population seems to be stable. International protection of coelacanths against commercial interests is needed 相似文献
6.
Malaria parasites do not contain or synthesize sialic acids 总被引:1,自引:0,他引:1
R Schauer M Wember R J Howard 《Hoppe-Seyler's Zeitschrift für physiologische Chemie》1984,365(2):185-194
The capacity of Plasmodia to synthesize sialic acids was investigated by adding radioactive acetate to short-term in vitro cultures of the intraerythrocytic asexual forms of three malaria parasites (the human malaria Plasmodium falciparum in Aotus trivirgatus erythrocytes; the simian malaria P. knowlesi in rhesus monkey erythrocytes; the rodent malaria P. berghei in mouse erythrocytes) and to cultures of extracellular zygotes of the avian malaria P. gallinaceum. Radioactive acetate was added to normal rhesus monkey erythrocytes and to cells of the murine myeloma NS-1 for comparison. Although [1-14C]-acetate labeled many proteins with each malaria parasite and the NS-1 cells, analysis of purified sialic acids revealed that only with the NS-1 cells was radioactivity incorporated into sialic acids. Furthermore, N-acetyl[6-3H]mannosamine was not incorporated into sialic acids or malarial glycoproteins when added to P. knowlesi cultures. All of the malaria parasites underwent growth or differentiation during these experiments as measured by [35S]methionine uptake into protein and by light microscopy. Extracellular parasites largely free of erythrocyte membranes were prepared to determine whether Plasmodia contain sialic acids that are not labeled by exogenous precursors. Purified merozoites of P. knowlesi and zygotes of P. gallinaceum did not contain detectable amounts of sialic acids on chemical analysis. Thus, although we could show that Plasmodia can incorporate radioactive sugars such as glucosamine, galactose and mannose into proteins, presumably glycoproteins, they do not synthesize sialic acids or sialo-glycoproteins, nor do they contain sialo-glycoconjugates of host origin. 相似文献
7.
Properties of human liver lysosomal sialidase 总被引:3,自引:0,他引:3
Sialidase in human liver was localized predominantly in the lysosomal fraction. Microsomal and nuclear fractions contained some activity but no cytosolic enzyme could be detected. The lysosomal enzyme fraction is active with gangliosides, fetuin, mucus glycoprotein, sialyllactose and other sialyloligosaccharides. The preferred rate of enzymic hydrolysis of sialyl linkages is alpha(2-3) greater than alpha(2-6) greater than alpha(2-8) and this is governed by the Vmax values, as Km values were similar for all substrates tested. N-Acetyl-neuraminic acid is released faster than N-glycoloylneuraminic acid. Using the inhibitors N-acetyl-2-deoxy-2,3-didehydroneuraminic acid and N-(4-nitrophenyl)oxamic acid with selected substrates the existence of at least two types of sialidase activity could be demonstrated. One is active preferentially with gangliosides and sialyllactose and the other with fetuin and sialyhexasaccharides. Strong inhibition by Cu2+ and Hg2+ was found with ganglioside and sialyllactose as substrates. The presence of a sialate O-acetylesterase acting on hematoside containing N-glycoloyl-4-O-acetylneuraminic acid was established. 相似文献
8.
9.
DNA regulatory elements for steroid hormones 总被引:19,自引:0,他引:19
10.
The N-terminal region of HIV-1 integrase is required for integration activity, but not for DNA-binding. 总被引:14,自引:0,他引:14
HIV-1 integrase binds to both double- and single-stranded DNA with Kd-values of around 20 nM, irrespective of sequence similarities with the termini of the viral LTR. For integration activity, however, the correct LTR sequence of the substrate is required. The putative zinc-binding site present at the N-terminus of the protein is not essential for DNA binding, since deletion mutants of the protein lacking this sequence show similar affinity towards DNA as the wild-type; however, these mutants are not capable of performing the LTR-cleavage and integration reactions. Thus, it appears that the N-terminal part of the integrase is essential for catalytic activity. 相似文献