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排序方式: 共有390条查询结果,搜索用时 31 毫秒
1.
Ana Isabell Paulino Aud Larsen Gunnar Bratbak Dale Evens Svein Rune Erga Einar Bye-Ingebrigtsen 《Marine Biology Research》2018,14(5):421-435
Changes in phytoplankton community composition potentially affect the entire marine food web. Because of seasonal cycles and inter-annual variations in species composition, long-term monitoring, covering many sequential years, is required to establish a baseline study and to reveal long-term trends. The current study describes the phytoplankton biomass variations and species composition in relation to hydrographic and meteorological conditions in the Raunefjord, western Norway, over a 6-year period from 2001 to 2006. The extent of inflow or upwelling in the fjord varied from year to year and resulted in pronounced differences in water column stability. The annual phytoplankton community succession showed some repeated seasonal patterns, but also high variability between years. Two to four diatom blooms were observed per year, and the spring blooms occurring before water column stratification in March were dominated by Skeletonema marinoi and Chaetoceros socialis, and other Chaetoceros and Thalassiosira spp. Blooms of the haptophytes Phaeocystis pouchetii and Emiliania huxleyi were irregular and in some years totally absent. Although E. huxleyi was present all year round it appeared in bloom concentrations only in 2003, when the summer was warm and the water column characterized by high surface temperatures and pronounced stratification. The annual average abundance of both diatoms and flagellates increased during the six years. Despite the high variation from year to year, our investigation provides valuable knowledge about annual phytoplankton community patterns in the region, and can be used as a reference to detect possible future changes. 相似文献
2.
Svein Valla Dag Hugo Coucheron Johs. Kjosbakken 《Molecular & general genetics : MGG》1987,208(1-2):76-83
Summary
Acetobacter xylinum contains a complex system of plasmid DNA molecules. Plasmids of molecular weights or copy numbers different from the original wild-type, are found in different types of mutants. Restriction endonuclease digestion and DNA/DNA hybridization analysis, showed that the plasmids often contained partly, but not completely the same DNA sequences. Two of these plasmid classes were analysed in more detail, and could be shown to differ in size by about 5 kb. Hybridization analysis using cloned DNA fragments as probes, showed that sequences lacking in the smallest plasmid were still present in a DNA fraction co-migrating with linearized chromosomal DNA. In addition, at least part of the DNA in the smallest plasmid was present both in the plasmid and chromosomal DNA fraction. Analysis of a particular strain containing an insertion of transposon Tn1, also indicated the existence of complex interactions between plasmids and chromosomal DNA. Together with experiments on conjugative transfer and curing of the plasmids, the results indicate that at least part of the genetic system of A. xylinum is unusual when compared to that of other genetically characterized bacteria. 相似文献
3.
Phosphate-Activated Glutaminase in the Crude Mitochondrial Fraction (P2 Fraction) from Human Brain Cortex 总被引:1,自引:1,他引:0
Gerd Svenneby Bjørg Roberg Svein Hogstad Ingeborg Aa. Torgner Elling Kvamme 《Journal of neurochemistry》1986,47(5):1351-1355
The kinetics and other properties of phosphate-activated glutaminase have for the first time been studied in the crude mitochondrial fraction (P2 fraction) from human brain. The enzyme is for unexplained reasons inactivated postmortem. The enzyme activity decreases by storing the tissue or homogenate at 37 degrees C. The inactivation is not caused by formation of a dialysable inhibiting compound. No large proteolytic degradation has occurred, since the phosphate-activated glutaminase-like immunoreactive band did not disappear during the storage. The molecular weight of the subunit of the enzyme as determined by immunoblots of sodium dodecyl sulfate-treated homogenates from human brain is estimated to be approximately 64 K. The enzyme has been shown to have a pH optimum of 8.6; it is activated by phosphate, inhibited by glutamate, and partially inhibited by ammonia. Double-inverse plots of enzyme activity against phosphate are concave-upward, and more so in the presence of an inhibitor. The inhibition by glutamate appears to be noncompetitive with the substrate glutamine, and competitive with the activator phosphate. These kinetic properties are not significantly different from our earlier observations concerning phosphate-activated glutaminase from pig brain and pig kidney. 相似文献
4.
5.
Ole Brix Astrid Bårdgard Svein Mathisen Nicholas Tyler Matti Nuutinen Sarveriò G. Condo Bruno Giardina 《Journal of comparative physiology. B, Biochemical, systemic, and environmental physiology》1990,159(6):655-660
Summary The oxygen binding of whole blood from humans and two arctic mammals, reindeer and muskox, has been studied as a function of carbon dioxide and temperature. All bloods display a marked Bohr effect with Bohr coefficients in the range –0.44––0.73. The Bohr effect is more pronounced at 20°C. The temperature sensitivity of reindeer and muskox blood expressed by the apparent heat of oxygenation, H, is almost three times lower than that of human HbA under the same experimental conditions. This thermodynamic difference gives special benefits to arctic mammals with large heterothermy by safeguarding oxygen unloading at very low ambient temperatures. 相似文献
6.
Cloning and expression of an Azotobacter vinelandii mannuronan C-5-epimerase gene. 总被引:2,自引:1,他引:1 下载免费PDF全文
An Azotobacter vinelandii mannuronan C-5-epimerase gene was cloned in Escherichia coli. This enzyme catalyzes the Ca(2+)-dependent epimerization of D-mannuronic acid residues in alginate to the corresponding epimer L-guluronic acid. The epimerase gene was identified by screening a bacteriophage EMBL3 gene library of A. vinelandii DNA with a synthetic oligonucleotide probe. The sequence of this probe was deduced after determination of the N-terminal amino acid sequence of a previously reported extracellular mannuronan C-5-epimerase from A. vinelandii. A DNA fragment hybridizing against the probe was subcloned in a plasmid vector in E. coli, and the corresponding recombinant plasmid expressed intracellular mannuronan C-5-epimerase in this host. The nucleotide sequence of the gene encoding the epimerase was determined, and the sequence data showed that the molecular mass of the deduced protein is 103 kDa. A module consisting of about 150 amino acids was repeated tandemly four times in the C-terminal part of the deduced protein. Each of the four repeats contained four to six tandemly oriented nonameric repeats. The sequences in these motifs are similar to the Ca(2+)-binding domains of functionally unrelated secreted proteins reported previously in other bacteria. The reaction product of the recombinant epimerase was analyzed by nuclear magnetic resonance spectroscopy, and the results showed that the guluronic acid residues were distributed in blocks along the polysaccharide chain. Such a nonrandom distribution pattern, which is important for the commercial use of alginate, has previously also been identified in the reaction product of the corresponding enzyme isolated from A. vinelandii. 相似文献
7.
The effective molecular weight cut-off values of dialysis membranes for carrageenan and alginate oligosaccharides were evaluated by gel permeation chromatography and nuclear magnetic resonance spectroscopy. For the different membranes tested, i.e. Medicell, Spectra Por 1000D and 3500D, the porous sizes are analogous to tri- and tetrasaccharides. A simple dialysis can be used to recover the majority of the oligosaccharides produced by a carrageenase or an alginate lyase digestion. 相似文献
8.
Identification of a locus involved in meningococcal lipopolysaccharide biosynthesis by deletion mutagenesis 总被引:4,自引:0,他引:4
Peter van der Ley Marco Kramer Liana Steeghs Betsy Kuipers Svein R. Andersen Michael P. Jennings E. Richard Moxon & Jan T. Poolman 《Molecular microbiology》1996,19(5):1117-1125
A novel method for insertion/deletion mutagenesis in meningococci was devised. This consisted of ligating a digest of total chromosomal DNA to a 1.1 kb restriction fragment containing an erythromycin-resistance marker ( ermC ), and subsequent transformation of the ligation mixture into the homologous meningococcal strain H44/76. Southern blotting of a number of the resulting erythromycin-resistant transformants demonstrated that all carried the ermC gene inserted at different positions in the chromosome. Mutants with a specific phenotype were identified by screening with the anti-lipopolysaccharide (LPS) monoclonal antibody MN4A8B2, which is specific for immunotype L3. In this way, two independent L3-negative mutant strains were isolated. In transformation experiments with chromosomal DNA from these mutants, erythromycin-resistance and lack of MN4A8B2 reactivity were always linked, showing that the insertion/deletion was in a locus involved in LPS biosynthesis. On SDS–PAGE, the mutant LPS displayed an electrophoretic mobility intermediate between that produced by the previously isolated galE and rfaF mutant strains. Chemical analysis of the mutant LPS revealed that the structure was probably lipid A–(KDO)2 –(Hep)2 . Chromosomal DNA flanking the ermC insertion in these two mutant strains was cloned, and used as probe for the isolation of the corresponding region of the wild-type strain. From hybridization and polymerase chain reaction (PCR) analysis, it could be concluded that both mutations map to the same locus. The affected gene probably encodes the glycosyltransferase necessary for adding N -acetylglucosamine to heptose. 相似文献
9.
Uptake of l-Glutamate into Rat Brain Synaptic Vesicles: Effect of Inhibitors that Bind Specifically to the Glutamate Transporter 总被引:2,自引:0,他引:2
Abstract: In this study we have described a series of new and potent inhibitors of the vesicular uptake of glutamate. The two most efficient inhibitors were the dyes Evans blue and Chicago Skye Blue 6B, which are structurally related to glutamate and were competitive inhibitors in the nanomolar range. The anion channel blocker 4,4'-diisothiocyanostilbene-2,2'-disulfonic acid (SITS) and the diuretics furosemide and bumetanide are inhibitors of chloride transport in other organs but were competitive inhibitors of glutamate and noncompetitive with respect to chloride ions. Evans blue, Chicago Skye Blue 6B, SITS, furosemide, and bumetanide are all large organic acids with two centers of negative charge and an electron-donating group at close vicinity of the negative charge at physiological pH. The inhibition of the glutamate uptake with these inhibitors was noncompetitive with respect to Cl− . The inhibitors, therefore, probably interact directly with the glutamate carrier. Bafilomycin A1 , which is a specific vacuolar ATPase inhibitor, was used as a control and inhibited the vesicular dopamine, glutamate, and GABA uptake to the same extent. None of the inhibitors had any effect on the plasma membrane carrier, which is therefore clearly different from the vesicular carrier. 相似文献
10.
A family of modular type mannuronan C-5-epimerase genes controls alginate structure in Azotobacter vinelandii 总被引:3,自引:1,他引:2
Helga Ertesvåg Hilde Kristin Høidal Ingrid Kathrin Hals Anne Rian Berit Doseth Svein Valla 《Molecular microbiology》1995,16(4):719-731
The ToxR protein is a transmembrane protein that regulates the expression of several virulence factors of Vibrio cholerae. Previous analysis of fusion proteins between ToxR and alkaline phosphatase (ToxR-PhoA) suggested that ToxR was active as a dimer. In order to determine whether dimerization of the ToxR periplasmic domain was essential for activity, this domain was replaced by monomeric and dimeric protein domains. Surprisingly, PhoA (dimeric), β-lactamase (monomeric, ToxR–Bla), or the leucine zipper of GCN4 (dimeric, ToxR-GCN4-M) could substitute functionally for the ToxR periplasmic domain. ToxR-GCN4 fusion proteins, in which the ToxR trans-membrane domain was eliminated (ToxR-GCN4-C), were inactive, but an additional fusion protein that contained a heterologous membrane-spanning domain retained activity. Strains containing each of these ToxR fusion proteins were analysed for in vivo colonization properties and response to in vitro growth conditions that are known to affect expression of the ToxR regulon. Strains containing ToxR-GCN4-M and ToxR-Bla responded like wild-type strains to in vitro growth conditions. In the infant-mouse colonization model, strains containing ToxR fusion proteins were all deficient in colonization relative to strains containing wild-type ToxR, and strains containing monomeric ToxR-Bla were most severely outcompeted. These results suggest that, under in vitro conditions, ToxR does not require a dimerized periplasmic domain, but that, under in vivo conditions, the correct conformation of the ToxR periplasmic domain may be more important for function. 相似文献