| 1. |
- Izumrudov, Vladimir, et al.
(författare)
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Factors Controlling Phase Separation in Water-Salt Solutions of DNA and Polycations.
- 2003
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Ingår i: Langmuir. - : American Chemical Society (ACS). - 0743-7463 .- 1520-5827. ; 19:11, s. 4733-4739
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Tidskriftsartikel (refereegranskat)abstract
- Factors affecting phase separation in water-salt solutions of polyelectrolyte complexes (PECs), formed by DNA and integral or pendant polycations with a quaternary amino group in every monomer unit, have been studied. When no salt was added, quantitative DNA precipitation occurred at a stoichiometric charge ratio, = [+]/[-] 1. In DNA mixtures with poly(N,N'-dimethyldiallylammonium chloride) (PDMDAAC, a pendant polycation), insoluble PECs formed in the range 0.7 < < 2. This suggests the formation of soluble, negatively charged PECs at 0 < < 0.7 and soluble, positively charged PECs at > 2. For different aliphatic ionene bromides (integral polycations), the range of corresponding to insoluble PECs was significantly broader, mainly due to the poor ability of the ionenes to form soluble, positively charged PECs. The range was also relatively broad for poly(N-ethyl-4-vinylpyridinium bromide) (a pendant polycation) and became broader with decreasing degree of polymerization of the polycation. The formation of insoluble PECs was favored by the addition of salt (NaCl), and the effect was more pronounced when decreasing the relative content of the solubilizing component, i.e., the nucleic acid at < 1 and the polycation at > 1. At moderate ionic strength, 0.12 M < [NaCl] < 0.6 M, quantitative precipitation of DNA was attained by addition of PDMAAC in the whole region studied: 1 < < 4.5. The data obtained strongly suggest that phase separation in solutions of DNA-containing PECs follows general rules revealed by studying PECs formed by flexible vinyl polyanions. However, the high rigidity of the DNA double helix appears to be responsible for the key feature revealed in the phase diagrams, i.e., significant broadening of the region for insoluble PECs at the expense of the region in which soluble DNA-containing PECs are formed. This feature may severely limit the application of DNA-containing PECs in medicine and biology but could be beneficial in the development of simple and effective procedures for DNA separation in biotechnology.
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| 2. |
- Moberg, Christina, et al.
(författare)
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De unga gör helt rätt när de stämmer staten
- 2022
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Ingår i: Aftonbladet. - 1103-9000.
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Tidskriftsartikel (populärvet., debatt m.m.)abstract
- 1 620 forskare och lärare i forskarvärlden: Vi ställer oss bakom Auroras klimatkrav
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| 3. |
- Wahlund, Per-Olof, et al.
(författare)
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Phase Separations in Water-Salt Solutions of Polyelectrolyte Complexes Formed by RNA and Polycations: Comparison with DNA Complexes.
- 2003
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Ingår i: Macromolecular Bioscience. - : Wiley. - 1616-5195 .- 1616-5187. ; 3:8, s. 404-411
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Tidskriftsartikel (refereegranskat)abstract
- Formation of insoluble polyelectrolyte complexes (PECs) between RNA and polycations was followed by measuring the residual RNA absorbance in the solution after separation of the precipitate. The polycations studied were poly(N,N-dimethyldiallylammonium) chloride (pendant type) and 2,5-ionene bromide (integral type) with quaternary amino groups in every monomer unit. The data obtained were compared with the results of analogous studies of DNA-containing PECs. This study is a part of a project aimed at the specific separation of plasmid DNA from RNA, a major problem in the preparative isolation of plasmid DNA. We thus deliberately chose a heterogenous RNA sample as it represents the RNA present in a real cell extract. In contrast to the exhaustive precipitation of DNA observed at certain values, a significant part of RNA was nonprecipitated at any = [+]/[-], that is, at any ratio of positively charged quaternary amino groups and negatively charged phosphate groups. The addition of sodium chloride increased the nonprecipitated fraction of RNA. DNA, on the other hand, was completely precipitated by both polycations at > 0.7. The less effective precipitation of RNA was probably due to the presence of a considerable fraction of short-chained molecules, incapable of forming a sufficient cooperative system of salt bonds with the polycation. This assumption was supported by a separate experiment, in which the precipitation behavior of RNA fractions of different molecular masses was investigated. The same tendency, while less pronounced, was also ascertained for PECs formed by polycations with DNA fractions of different molecular masses. The possibility of using the revealed differences between DNA and RNA behavior for effective precipitation procedure useful in bioseparation is discussed. The difference in the precipitation behavior of nucleic acids of different molecular masses means there is a possibility for developing an enzymatic assay for DNAase and RNAase activity.
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| 4. |
- Wahlund, Per-Olof, et al.
(författare)
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Polyelectrolyte complexes as a tool for purification of plasmid DNA background and development
- 2004
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Ingår i: Journal of Chromatography. B. - : Elsevier BV. - 1873-376X .- 1570-0232. ; 807:1, s. 121-127
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Tidskriftsartikel (refereegranskat)abstract
- The demand for highly purified plasmids in gene therapy and plasmid-based vaccines requires large-scale production of pharmaceutical-grade plasmid. Plasmid DNA was selectively precipitated from a clarified alkaline lysate using the polycation poly(N,N'-dimethyldiallylammonium) chloride which formed insoluble polyelectrolyte complex (PEC) with the plasmid DNA. Soluble PECs of DNA with polycations have earlier been used for cell transformation, but now the focus has been on insoluble PECs. Both DNA and RNA form stable PECs with synthetic polycations. However, it was possible to find a range of salt concentration where plasmid DNA was quantitatively precipitated whereas RNA remained in solution. The precipitated plasmid DNA was resolubilised at high salt concentration and the polycation was removed by gel-filtration. (C) 2004 Elsevier B.V. All rights reserved.
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| 5. |
- Wahlund, Per-Olof, et al.
(författare)
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Precipitation by polycation as capture step in purification of plasmid DNA from a clarified lysate
- 2004
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Ingår i: Biotechnology and Bioengineering. - : Wiley. - 1097-0290 .- 0006-3592. ; 87:5, s. 675-684
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Tidskriftsartikel (refereegranskat)abstract
- The demand for highly purified plasmids in gene therapy and plasmid-based vaccines requires large-scale production of pharmaceutical-grade plasmid. Large-scale purification of plasmid DNA from bacterial cell culture normally includes one or several chromatographic steps. Prechromatographic steps include precipitation with solvents, salts, and polymers combined with enzymatic degradation of nucleic acids. No method alone has so far been able to selectively capture plasmid DNA directly from a clarified alkaline lysate. We present a method for selective precipitation of plasmid DNA from a clarified alkaline lysate using polycation poly(N,N'-dimethyldiallylammonium) chloride (PDMDAAC). The specific interaction between the polycation and the plasmid DNA resulted in the formation of a stoichiometric insoluble complex. Efficient removal of contaminants such as RNA, by far the major contaminant in a clarified lysate, and proteins as well as 20-fold plasmid concentration has been obtained with about 80% recovery. The method utilizes a inexpensive, commercially available polymer and thus provides a capture step suitable for large-scale production. (C) 2004 Wiley Periodicals, Inc.
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| 6. |
- Eliasson, Lena, et al.
(författare)
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PKC-dependent stimulation of exocytosis by sulfonylureas in pancreatic beta cells
- 1996
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Ingår i: Science. - : American Association for the Advancement of Science (AAAS). - 1095-9203 .- 0036-8075. ; 271:5250, s. 813-815
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Tidskriftsartikel (refereegranskat)abstract
- Hypoglycemic sulfonylureas represent a group of clinically useful antidiabetic compounds that stimulate insulin secretion from pancreatic beta cells. The molecular mechanisms involved are not fully understood but are believed to involve inhibition of potassium channels sensitive to adenosine triphosphate (KATP channels) in the beta cell membrane, causing membrane depolarization, calcium influx, and activation of the secretory machinery. In addition to these effects, sulfonylureas also promoted exocytosis by direct interaction with the secretory machinery not involving closure of the plasma membrane KATP channels. This effect was dependent on protein kinase C (PKC) and was observed at therapeutic concentrations of sulfonylureas, which suggests that it contributes to their hypoglycemic action in diabetics.
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| 7. |
- Larsson, Mats, et al.
(författare)
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Magnetic field effects on optical and transport properties in InAs/GaAs quantum dots
- 2006
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Ingår i: Physical Review B. - 1098-0121. ; 74:24
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Tidskriftsartikel (refereegranskat)abstract
- A photoluminescence study of self-assembled InAs/GaAs quantum dots under the influence of magnetic fields perpendicular and parallel to the dot layer is presented. At low temperatures, the magnetic field perpendicular to the dot layer alters the in-plane transport properties due to localization of carriers in wetting layer (WL) potential fluctuations. Decreased transport in the WL results in a reduced capture into the quantum dots and consequently a weakened dot-related emission. The effect of the magnetic field exhibits a considerable dot density dependence, which confirms the correlation to the in-plane transport properties. An interesting effect is observed at temperatures above approximately 100 K, for which magnetic fields, both perpendicular and parallel to the dot layer, induced an increment of the quantum dot photoluminescence. This effect is ascribed to the magnetic confinement of the exciton wave function, which increases the probability for carrier capture and localization in the dot, but affects also the radiative recombination with a reduced radiative lifetime in the dots under magnetic compression.
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| 8. |
- Zamora, Juan Carlos, et al.
(författare)
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Considerations and consequences of allowing DNA sequence data as types of fungal taxa
- 2018
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Ingår i: IMA Fungus. - : INT MYCOLOGICAL ASSOC. - 2210-6340 .- 2210-6359. ; 9:1, s. 167-185
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Tidskriftsartikel (refereegranskat)abstract
- Nomenclatural type definitions are one of the most important concepts in biological nomenclature. Being physical objects that can be re-studied by other researchers, types permanently link taxonomy (an artificial agreement to classify biological diversity) with nomenclature (an artificial agreement to name biological diversity). Two proposals to amend the International Code of Nomenclature for algae, fungi, and plants (ICN), allowing DNA sequences alone (of any region and extent) to serve as types of taxon names for voucherless fungi (mainly putative taxa from environmental DNA sequences), have been submitted to be voted on at the 11th International Mycological Congress (Puerto Rico, July 2018). We consider various genetic processes affecting the distribution of alleles among taxa and find that alleles may not consistently and uniquely represent the species within which they are contained. Should the proposals be accepted, the meaning of nomenclatural types would change in a fundamental way from physical objects as sources of data to the data themselves. Such changes are conducive to irreproducible science, the potential typification on artefactual data, and massive creation of names with low information content, ultimately causing nomenclatural instability and unnecessary work for future researchers that would stall future explorations of fungal diversity. We conclude that the acceptance of DNA sequences alone as types of names of taxa, under the terms used in the current proposals, is unnecessary and would not solve the problem of naming putative taxa known only from DNA sequences in a scientifically defensible way. As an alternative, we highlight the use of formulas for naming putative taxa (candidate taxa) that do not require any modification of the ICN.
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| 9. |
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| 10. |
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| 11. |
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| 12. |
- Bergenstråhle-Wohlert, Malin, et al.
(författare)
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Concentration enrichment of urea at cellulose surfaces : results from molecular dynamics simulations and NMR spectroscopy
- 2012
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Ingår i: Cellulose. - : Springer Science and Business Media LLC. - 0969-0239 .- 1572-882X. ; 19:1, s. 1-12
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Tidskriftsartikel (refereegranskat)abstract
- A combined solid-state NMR and Molecular Dynamics simulation study of cellulose in urea aqueous solution and in pure water was conducted. It was found that the local concentration of urea is significantly enhanced at the cellulose/solution interface. There, urea molecules interact directly with the cellulose through both hydrogen bonds and favorable dispersion interactions, which seem to be the driving force behind the aggregation. The CP/MAS (13)C spectra was affected by the presence of urea at high concentrations, most notably the signal at 83.4 ppm, which has previously been assigned to C4 atoms in cellulose chains located at surfaces parallel to the (110) crystallographic plane of the cellulose I beta crystal. Also dynamic properties of the cellulose surfaces, probed by spin-lattice relaxation time (13)CT (1) measurements of C4 atoms, are affected by the addition of urea. Molecular Dynamics simulations reproduce the trends of the T (1) measurements and lends new support to the assignment of signals from individual surfaces. That urea in solution is interacting directly with cellulose may have implications on our understanding of the mechanisms behind cellulose dissolution in alkali/urea aqueous solutions.
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| 13. |
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| 14. |
- Berglund, Olof, et al.
(författare)
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Persistent organic pollutants in river food webs: influence of trophic position and degree of heterotrophy
- 2005
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Ingår i: Canadian Journal of Fisheries and Aquatic Sciences. - 1205-7533. ; 62:9, s. 2021-2032
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Tidskriftsartikel (refereegranskat)abstract
- We investigated how the degree of autotrophy/heterotrophy and organism trophic position influenced the bioaccumulation of polychlorinated biphenyls (PCBs) in 10 benthic river food webs consisting of terrestrial detritus, periphyton, invertebrates, and age-0 brown trout (Salmo trutta) in southern Sweden. Concentrations of PCBs increased with trophic position, estimated from delta(15)N and delta(13)C, on a dry weight basis (ng center dot g(-1) dry weight) but not on a lipid weight basis (ng center dot g(-1) lipid). PCB biomagnification factors between the first and second trophic levels (invertebrates/ periphyton and invertebrates/detritus) ranged between 0.3 and 2.3 and between the second and third levels (trout/invertebrates) between 0.3 and 2.0 on a lipid weight basis. The mean proportion of carbon ultimately derived from terrestrial sources, alpha, was 0.82 +/- 0.19 for invertebrates and 0.67 +/- 0.28 for trout. Contrary to our hypothesis, PCB concentrations in trout were positively related to alpha (r(2) = 0.58-0.77, p < 0.05). As alpha and the periphyton density (g C center dot m(-2)) in the rivers was positively related (r(2) = 0.88, p < 0.01), we propose that this relationship was due to an increased retention and exposure of PCBs to trout in rivers with low grazing pressure and high periphyton density.
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| 15. |
- Engstedt, Olof, 1980-, et al.
(författare)
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Annual spawning migration of anadromous pike (Esox lucius L.) in streams entering the Baltic Sea
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Annan publikation (övrigt vetenskapligt/konstnärligt)abstract
- The movement of pike (n = 3415) was investigated in four streams entering the Baltic Sea in the Kalmar Sound region, Sweden. Migration patterns were monitored during spawning in three of the streams and during the whole year in the forth stream using passive integrated transponders and outer tags. The study was conducted yearly between 2006 and 2010. Mature pike returned (22 – 45%) to the same streams year after year and some fish returned to the same regions of the streams. No incidence of fish visiting another stream than the one where they were marked was recorded and no fish missed the spawning season to return the next year. These results indicated that the reason for fish not returning was due to mortality. The proportions of returning fish indicated homing and the spawning ground fidelity (stream) was high. Return rates were influenced by size of fish, sex and stream identity. We also investigated if sex, size or individual behaviour influenced timing of arrival, departure or duration of stay in freshwater. Diurnal activity was examined in one year in each stream suggesting activity peaks in the morning and evening. The results show that pike in the Baltic Sea are anadromous and that the migration behavior is likely to create barriers for gene flow. The separation in populations by spawning are similar to salmonid species and the management of pike in the Baltic Sea must consider this process in strategies and plans of fishing.
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| 16. |
- Engstedt, Olof, 1980-, et al.
(författare)
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Experimental validation of Sr uptake in juvenile pike (Esox Lucius L.) otoliths – from water and food.
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Annan publikation (övrigt vetenskapligt/konstnärligt)abstract
- Strontium (Sr) or Sr:Ca ratios in otoliths have been widely used in the last decade to describe migration histories of fish between fresh and marine waters. However, reference experimental studies on particular species and waters are necessary to confirm the underlying assumption and evaluate the usefulness of this tool for field data. We conducted an experiment with the aim to answer these questions for anadromous pike (Esox lucius L.) in the Baltic Sea. Juvenile pike were reared in successively increasing salinities (10 steps from 0 to 7 ‰) for 110 days, and then in constant maximum salinity (7 ‰) for an additional 50 days. Pikes in the experiment were divided into two food treatments, given prey fish from brackish environments (7 ‰) and fish from freshwater lakes. Sr:Ca in pike otoliths were positively related to Sr in water (i.e salinity) in both treatments, suggesting that Sr:Ca ratios may be used to describe migration histories between rivers and the Baltic Sea. A significant difference in Sr.Ca ratios was found between the food treatments, showing that differences in diet may contribute to variation in otolith Sr:Ca, at least for pike in the Baltic Sea. Maximum Sr:Ca values for pike given marine food corresponded with field collected fish from the Baltic Sea.
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| 17. |
- Engstedt, Olof, 1980-, et al.
(författare)
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Strontium (Sr) uptake from water and food in otoliths of juvenile pike (Esox lucius L.)
- 2012
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Ingår i: Journal of Experimental Marine Biology and Ecology. - : Elsevier. - 0022-0981 .- 1879-1697. ; 418-419, s. 69-74
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Tidskriftsartikel (refereegranskat)abstract
- The strontium (Sr) or Sr:Ca ratio in otoliths has been widely used in the last decade to describe the migration histories of fish between fresh and marine waters. However, reference experimental studies of particular species and waters are necessary to confirm the underlying assumptions and evaluate the applicability of this tool to field data. Laboratory experiments indicated that juvenile, anadromous pike (Esox lucius L) from the Baltic Sea reared in successively increasing salinities (from 0 to 7 parts per thousand) for 110 d accumulated Sr in their otoliths according to a positive relationship with waterborne Sr. When the pike were given prey fish from brackish (7 parts per thousand) environments, the otolith Sr:Ca ratio increased more than in fish given prey from freshwater lakes. Pike held at constant salinity (7 parts per thousand) and given prey fish from the same salinity environment had an Sr:Ca ratio of 6.9 x 10(-3). The ratio decreased successively for fish given prey from freshwater (4.4 x 10(-3)) or kept in freshwater and given food from brackish water (3.1 x 10(-3)). Fish exposed to freshwater and given prey fish from freshwater displayed no increase in Sr:Ca ratio (1.6 x 10(-3)). The experiments demonstrated that the Sr:Ca ratio may be used to describe the migration history of pike between rivers and the Baltic Sea. The maximum Sr:Ca value for pike given marine-origin food corresponded to those of fish collected from the Baltic Sea.
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| 18. |
- Grubb, Anders, et al.
(författare)
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Generation of a new cystatin C-based estimating equation for glomerular filtration rate by use of 7 assays standardized to the international calibrator
- 2014
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Ingår i: Clinical Chemistry. - : Oxford University Press (OUP). - 0009-9147 .- 1530-8561. ; 60:7, s. 974-986
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Tidskriftsartikel (refereegranskat)abstract
- BACKGROUND:Many different cystatin C-based equations exist for estimating glomerular filtration rate. Major reasons for this are the previous lack of an international cystatin C calibrator and the nonequivalence of results from different cystatin C assays.METHODS:Use of the recently introduced certified reference material, ERM-DA471/IFCC, and further work to achieve high agreement and equivalence of 7 commercially available cystatin C assays allowed a substantial decrease of the CV of the assays, as defined by their performance in an external quality assessment for clinical laboratory investigations. By use of 2 of these assays and a population of 4690 subjects, with large subpopulations of children and Asian and Caucasian adults, with their GFR determined by either renal or plasma inulin clearance or plasma iohexol clearance, we attempted to produce a virtually assay-independent simple cystatin C-based equation for estimation of GFR.RESULTS:We developed a simple cystatin C-based equation for estimation of GFR comprising only 2 variables, cystatin C concentration and age. No terms for race and sex are required for optimal diagnostic performance. The equation, [Formula: see text] is also biologically oriented, with 1 term for the theoretical renal clearance of small molecules and 1 constant for extrarenal clearance of cystatin C.CONCLUSIONS:A virtually assay-independent simple cystatin C-based and biologically oriented equation for estimation of GFR, without terms for sex and race, was produced.
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| 19. |
- Gustavsson, Per-Erik, et al.
(författare)
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Continuous superporous agarose beds for chromatography and electrophoresis
- 1999
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Ingår i: Journal of chromatography. A. - 0021-9673. ; 832:1-2, s. 29-39
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Tidskriftsartikel (refereegranskat)abstract
- Continuous agarose beds (monoliths) were prepared by casting agarose emulsions designed to generate superporous agarose. The gel structures obtained were transected by superpores (diameters could be varied in the range 20–200 μm) through which liquids could be pumped. The pore structure and the basic properties of the continuous gel were investigated by microscopy and size exclusion chromatography. The chromatographic behaviour was approximately the same as for beds packed with homogeneous agarose beads with a particle diameter equivalent to the distance between the superpores. In one application, the superporous continuous agarose bed was derivatized with a NAD+ analogue and used in the affinity purification of bovine lactate dehydrogenase from a crude extract. In another application, a new superporous composite gel material was prepared by adding hydroxyapatite particles to the agarose phase. The composite bed was used to separate a protein mixture by hydroxyapatite chromatography. In a third application, the continuous superporous agarose material was used as an electrophoresis gel. Here, a water-immiscible organic liquid was pumped through the superpores to dissipate the joule heat evolved, thus allowing high current densities.
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| 20. |
- Gustavsson, Per-Erik, et al.
(författare)
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Continuous superporous agarose beds in radial flow columns
- 2001
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Ingår i: Journal of chromatography. A. - 0021-9673. ; 925:1-2, s. 69-78
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Tidskriftsartikel (refereegranskat)abstract
- Continuous superporous agarose beds constitute a new support material for chromatography, biocatalysis and electrophoresis. The bed consists of a single piece of agarose gel, homogeneously transected by flow-carrying pores, which easily can be varied in the range of 10–100 μm. In this work, large diameter beds (60 mm) were prepared and used in specially designed radial flow columns. The basic chromatographic properties of the beds were investigated by size-exclusion chromatography experiments. In an affinity chromatography application one bed was derivatized with Cibacron Blue 3GA and used for the purification of lactate dehydrogenase from a crude bovine heart extract. In a biotransformation application one bed was provided with immobilized β-galactosidase and used in the production of lactose-free milk.
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| 21. |
- Gustavsson, Per-Erik, et al.
(författare)
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Direct measurements of convective fluid velocities in superporous agarose beads
- 1998
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Ingår i: Journal of Chromatography A. - 0021-9673. ; 795:2, s. 199-210
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Tidskriftsartikel (refereegranskat)abstract
- Superporous agarose beads contain two sets of pores, diffusion pores and so-called superpores or flow pores, in which the chromatographic flow can transport substances to the interior of each individual bead [Gustavsson and Larsson, J. Chromatogr. A 734 (1996) 231]. The existence of pore flow may be proven indirectly by the chromatographic performance of beads but it has never been directly demonstrated in a chromatographic bed. In this report, pore flow was directly measured by following the movement of micro-particles (dyed yeast cells) in a packed bed. The passage of the micro-particles through the superpores and through the interstitial pores was followed by a microscope/video camera focused on beads which were situated four layers from the glass wall. The video recordings were subsequently used to determine the convective fluid velocities in both the superpores and the interstitial pores. Experiments were carried out with three different bead size ranges, all of which contained superporous beads having an average superpore diameter of 30 mu m. The superpore fluid velocity as % of interstitial fluid velocity was determined to be 2-5% for columns packed with 300-500-mu m beads (3% average value), 6-12% for columns packed with 180-300 mu m beads (7% average value) and 11-24% for columns packed with 106-180-mu m beads (17% average value). These data were compared to and found to agree with theoretically calculated values based on the Kozeny-Carman equation. In order to observe and accurately measure fluid velocities within a chromatographic bed, special techniques were adopted. Also, precautions were made to ensure that the experimental conditions used were representative of normal chromatography runs. (C) 1998 Elsevier Science B.V.
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| 22. |
- Gustavsson, Per-Erik, et al.
(författare)
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Fast Chromatography of Proteins.
- 2003
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Ingår i: Isolation and Purification of proteins. (Biotechnology and Bioprocessing ; 27). - 0824707265 ; , s. 423-454
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Bokkapitel (övrigt vetenskapligt/konstnärligt)abstract
- Abstract is not available
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| 23. |
- Gustavsson, Per-Erik, et al.
(författare)
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Monolithic Polysaccharide Materials.
- 2003
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Ingår i: Monolithic Materials: Preparation, Properties and Applications (Journal of Chromatography Library ; 67). - 0444508791 ; 67
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Bokkapitel (övrigt vetenskapligt/konstnärligt)abstract
- Abstract is not available
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| 24. |
- Gustavsson, Per-Erik, et al.
(författare)
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Purification of plasmid DNA with a new type of anion-exchange beads having a non-charged surface
- 2004
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Ingår i: Journal of Chromatography A. - : Elsevier BV. - 0021-9673. ; 1038:1-2, s. 131-140
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Tidskriftsartikel (refereegranskat)abstract
- We have prepared a new type of anion exchanger, which effectively discriminates between RNA and plasmid DNA. The material is based on a Sephacryl S-500 HR matrix provided with quartenary amine anion-exchange groups. A distinguishing feature of the beads is that a thin (2-3 mum) outer layer of the beads lacks ion-exchange groups. In the synthesis of these beads the vinyl groups in the outer layer of vinylalkyl substituted Sephacryl S-500 HR beads are reacted with bromine. The resulting layer of bromoalkyl groups are hydrolysed, creating an inert outer layer of hydroxyalkyl groups. Finally, bromination and trimethylamine reactions of the inner vinyl groups provide the beads with a core of cationic groups. Large plasmid molecules will not bind to such beads since they are too large to enter the pores and therefore cannot come into contact with the charged matrix in the inner parts of the beads. RNA and protein molecules present in a cleared lysate, on the other hand, readily enter the pores and become adsorbed. A two-column strategy was developed for plasmid purification (recombinant pBluescript, 5.9 kilo base pairs, kbp). The first column was packed with the restricted access anion-exchanger beads (lid beads) and the second column with normal ion-exchange material (same ligand density as the lid beads). Diluted (3 x), cleared lysate was pumped through the tandem columns. The first column was subsequently disconnected from the system and the purified plasmid adsorbed on the second column was eluted in a concentrated form (6x) and with 89% recovery. The two-column procedure removed 99.5% of the RNA and 96% of the proteins. (C) 2004 Elsevier B.V. All rights reserved.
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| 25. |
- Gustavsson, Per-Erik, et al.
(författare)
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Superporous agarose, a new material for chromatography
- 1996
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Ingår i: Journal of chromatography. A. - : Elsevier BV. - 0021-9673. ; 734:2, s. 231-240
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Tidskriftsartikel (refereegranskat)abstract
- This paper reports on a new type of spherical agarose chromatography particles characterized by two sets of pores, normal diffusion pores, characteristic of all agarose materials and very wide pores, so-called superpores or flow pores. These superpores allow part of the chromatographic flow to pass through each individual particle, which gives improved mass transfer, especially in situations where diffusion is the limiting factor for the overall performance of a chromatographic separation. The particles were prepared by a double emulsification procedure. Observations under a microscope and size-exclusion chromatography were used in order to demonstrate pore flow. The chromatographic behaviour of the new particles was as efficient as that of homogeneous particles which were several times smaller. The agarose particles were derivatized with polyethyleneimine and used for an ion-exchange chromatographic separation of three model proteins. As expected from a perfusion material, the superporous beads resolved the protein mixture more efficiently than homogeneous beads of the same size.
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| 26. |
- Gustavsson, Per-Erik, et al.
(författare)
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Superporous agarose as an affinity chromatography support
- 1997
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Ingår i: Journal of chromatography. A. - 0021-9673. ; 776:2, s. 197-203
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Tidskriftsartikel (refereegranskat)abstract
- Superporous agarose beads were used as an affinity support in column chromatography. These beads characteristically possess two sets of pores, normal diffusion pores and flow pores, so-called superpores. The superpores, whose diameter is a substantial fraction of the particle diameter (i.e. 1/3 to 1/10 of the particle diameter), allow part of the chromatographic flow to pass through each individual bead. Consequently, significant improvement in mass transfer is observed in superporous beads as compared with homogeneous beads, especially at high flow-rates [Gustavsson and Larsson, J. Chromatogr. A, 734 (1996) 231–240.]Superporous agarose beads and homogeneous agarose beads were each derivatized with two types of affinity ligands. A NAD+ analogue was used for the purification of bovine lactate dehydrogenase and protein A was used for the adsorption of rabbit IgG. The performances of superporous beads and homogeneous beads were compared. Superporous bead columns derivatized with protein A and NAD+ analogue could be operated 5 times and 3 times, respectively, as fast as corresponding homogeneous bead columns.
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| 27. |
- Gustavsson, Per-Erik, et al.
(författare)
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Superporous agarose beads as a hydrophobic interaction chromatography support
- 1999
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Ingår i: Journal of Chromatography A. - 0021-9673. ; 830:2, s. 275-284
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Tidskriftsartikel (refereegranskat)abstract
- Superporous agarose beads were used as a support for hydrophobic interaction chromatography. These beads have large connecting flow pores in addition to their normal diffusion pores. The flow pores, which are approximately one fifth of the overall diameter of the superporous agarose beads, were earlier shown to give the beads improved mass transfer properties relative to homogeneous agarose beads (Gustavsson and Larsson, J. Chromatogr. A, 734 (1996) 231-240). Superporous agarose beads and homogeneous agarose beads of the same particle size range (106-180 mu m) were derivatized with phenyl groups. The properties of the superporous beads were then compared with the homogeneous beads in the separation of a mixture of three model proteins (ribonuclease A, lysozyme and bovine serum albumin) at various superficial flow velocities from 30 to 600 cm/h. The superporous beads gave satisfactory separation at flow velocities five times higher than was possible for homogeneous beads. The performance of the two types of beads was also compared in the purification of lactate dehydrogenase from a beef heart extract at a superficial flow velocity of 150 cm/h. The superporous beads performed considerably better, leading to twice the purification factor and twice the concentration of the desired product. The results were interpreted using the theoretical treatment given by Carta and Rodrigues (Carta and Rodrigues, Chem. Eng. Sci., 48 (1993) 3927). (C) 1999 Elsevier Science B.V. All rights reserved.
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| 28. |
- Haby, Christelle, et al.
(författare)
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Inhibition of serine/threonine protein phosphatases promotes opening of voltage-activated L-type Ca2+ channels in insulin-secreting cells
- 1994
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Ingår i: Biochemical Journal. - 0264-6021 .- 1470-8728. ; 298:Pt 2, s. 341-346
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Tidskriftsartikel (refereegranskat)abstract
- The biological activity of many proteins, including voltage-sensitive ion channels, is controlled by their state of phosphorylation. Ca2+ influx through voltage-activated L-type Ca2+ channels serves as the major stimulatory signal in insulin-secreting cells. We have now investigated the extent to which Ca2+ handling in clonal insulin-secreting RiNm5F cells was affected by okadaic acid, an inhibitor of various serine/threonine protein phosphatases. Whole-cell patch-clamp experiments showed that okadaic acid generated an increase in membrane current, suggesting that it promotes Ca2+ influx through L-type voltage-gated Ca2+ channels probably by modifying their phosphorylation state. Okadaic acid was found to provoke a transient rise in the cytoplasmic free Ca2+ concentration ([Ca2+]i) but had no further effect on the K(+)-induced increase. The Ca2+ transient induced by okadaic acid was dependent on the presence of extracellular Ca2+ and was abolished by D600, a blocker of voltage-activated L-type Ca2+ channels. Concomitant with the rise in [Ca2+]i, okadaic acid induced insulin secretion, a phenomenon that was also dependent on extracellular Ca2+. It is proposed that hyperphosphorylation of voltage-activated L-type Ca2+ channels in insulin-secreting cells lowers the threshold potential for their activation.
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| 29. |
- Hiensch, Martin, et al.
(författare)
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Two-material rail development : field test results regarding rolling contact fatigue and squeal behaviour
- 2005
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Ingår i: Wear. - : Elsevier BV. - 0043-1648 .- 1873-2577. ; 258:7-8, s. 964-972
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Tidskriftsartikel (refereegranskat)abstract
- Results from the European 5th Framework project “InfraStar” are presented. The InfraStar project is developing a two-material rail to increase the productivity and reliability of rail infrastructure. The two-material rail aims to be rolling contact fatigue (RCF) resistant and to reduce squeal noise.The InfraStar consortium has built a high level of wheel–rail expertise and understanding regarding RCF initiation and development, level and position of wheel–rail contact forces, and new interface materials and has gained experience in both laboratory and field test operating conditions. Within the project a validated theoretical train–track interaction model and a fatigue design model for two-material rails have been developed.This paper focuses on the field test results of the two-material rail, and how the predictions and expectations from the selection process match with the results observed in track. Results are very promising. The two-material rail prototypes, now over 1 year in track, show no RCF damage where the non-treated rail shows clear RCF damage. The development of the application process and other objectives of the InfraStar project are discussed.
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| 30. |
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| 31. |
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| 32. |
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| 33. |
- Holmqvist, Niklas, et al.
(författare)
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Lake trophic status and bioaccumulation of polychlorinated biphenyls in benthic organisms: a comparison between littoral and profundal invertebrates
- 2005
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Ingår i: Canadian Journal of Fisheries and Aquatic Sciences. - 1205-7533. ; 62:6, s. 1201-1209
-
Tidskriftsartikel (refereegranskat)abstract
- We investigated the influence of lake trophic status on accumulation of polychlorinated biphenyls (PCBs) in littoral and profundal invertebrates from 19 lakes in southern Sweden. The PCB concentration in profundal chironomids (Chironomus sp.) was negatively correlated with lake trophy but the concentration in littoral crayfish (Pacifasticus leniusculus) was unrelated to shifting nutrient regimes. PCB concentrations in chironomids were negatively correlated, while crayfish did not correlate with lake total phosphorus. Two findings indicate that different processes determine bioaccumulation in littoral and profundal invertebrates: (i) a lack of correlation between PCB concentrations in crayfish and chironomids within lakes and (ii) some differences in congener distribution in the two species. We suggest a possible explanation in that chironomids are directly exposed to settling material from the pelagic zone, while crayfish are omnivorous and feed mainly in the littoral zone. A intensive investigation on one pond population could not reveal any individual factors, such as lipid content, size, or sex, influencing bioaccumulation of PCBs in crayfish.
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| 34. |
- Holmqvist, Niklas, et al.
(författare)
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Low levels of persistent organic pollutants (POPS) in New Zealand eels reflect isolation from atmospheric sources
- 2006
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Ingår i: Environmental Pollution. - : Elsevier BV. - 0269-7491. ; 141:3, s. 532-538
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Tidskriftsartikel (refereegranskat)abstract
- Polychlorinated biphenyls (PCBs) and organic pesticides (i.e., DDTs) were measured in long finned eels (Anguilla dieffenbachii) in 17 streams on the west coast of South Island, New Zealand. Very low levels of PCBs and low levels of ppDDE were found. The concentrations of PCBs and ppDDE were not correlated within sites indicating that different processes determined the levels of the two pollutants in New Zealand eels. The PCBs probably originate from atmospheric transport, ppDDE levels are determined by land use and are higher in agriculture areas. The low contamination level of these aquatic systems seems to be a function of a low input from both long and short-range transport as well as few local point sources. No correlation could be found between lipid content and persistent organic pollutants (POPs) concentration (as shown in previous studies) in the eels which could be explained by low and irregular intake of the pollutants.
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| 35. |
- Holmqvist, Niklas, et al.
(författare)
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Persistent organic pollutants (POP) in a benthic omnivore - A comparison between lake and stream crayfish populations
- 2007
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Ingår i: Chemosphere. - : Elsevier BV. - 1879-1298 .- 0045-6535. ; 66:6, s. 1070-1078
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Tidskriftsartikel (refereegranskat)abstract
- We investigated the accumulation of PCB and DDT in crayfish populations in 10 streams in southern Sweden. The results were compared with an earlier study on crayfish in lakes from the same area. We found that the concentration of pollutants in crayfish did not differ between the two types of systems. Variation in body burden was higher in stream living crayfish probably because of the higher influence from pollutants deposited in the catchment area and the more dynamic transport in streams. In streams, pp'-DDE concentrations were positively correlated to trophic status (total phosphorous) while PCB did not show any correlation with the nutrient regime. Further, mean Sigma PCB and p,p'-DDE concentrations in crayfish did not correlate in streams. We suggest that the sources of the two pollutants differ for stream living crayfish. The results indicate that crayfish in streams are affected to a higher degree to pollutants in the catchment area and the precipitation regime. In lakes, internal processes govern uptake of pollutants in crayfish.
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| 36. |
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| 37. |
- Islam, M. Shahidul, et al.
(författare)
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Cyclic ADP-ribose in beta cells
- 1993
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Ingår i: Science. - 0036-8075 .- 1095-9203. ; 262:5133, s. 584-586
-
Tidskriftsartikel (refereegranskat)
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| 38. |
- Islam, M. Shahidul, et al.
(författare)
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Sulfhydryl oxidation induces rapid and reversible closure of the ATP-regulated K+ channel in the pancreatic beta-cell
- 1993
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Ingår i: FEBS Letters. - 0014-5793 .- 1873-3468. ; 319:1-2, s. 128-132
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Tidskriftsartikel (refereegranskat)abstract
- Effects of sulfhydryl modification on the ATP regulated K+ channel (KATP channel) in the pancreatic beta-cell were studied, using the patch clamp technique. Application of the sulfhydryl oxidizing agents thimerosal and 2,2'-dithio-bis(5-nitropyridine) (DTBNP), in micromolar concentrations, caused complete inhibition of the KATP channel, in inside-out patches. The inhibition was rapid and was reversed by the disulfide reducing agents dithiothreitol and cysteine. Thimerosal, which is poorly membrane permeable, inhibited channel activity, only when applied to the intracellular face of the plasma membrane. In contrast, DTBNP, which is highly lipophilic, caused closure of the KATP channel and consequent depolarization of the membrane potential, also when applied extracellularly. Our results indicate the presence of accessible free SH groups on the cytoplasmic side of the KATP channel in the pancreatic beta-cell. These SH groups are essential for channel function and it is possible that thiol-dependent redox mechanisms can modulate KATP channel activity.
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| 39. |
- Islam, M. Shahidul, et al.
(författare)
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Thiol oxidation by 2,2'-dithiodipyridine causes a reversible increase in cytoplasmic free Ca2+ concentration in pancreatic beta-cells : Role for inositol 1,4,5-trisphosphate-sensitive Ca2+ stores
- 1997
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Ingår i: Biochemical Journal. - : Portland Press Ltd.. - 0264-6021 .- 1470-8728. ; 321:Pt 2, s. 347-354
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Tidskriftsartikel (refereegranskat)abstract
- 2,2'-Dithiodipyridine (2,2'-DTDP), a reactive disulphide that mobilizes Ca2+ from ryanodine-sensitive Ca2+ stores in muscle, induced a biphasic increase in cytoplasmic free Ca2+ concentration ([Ca2+]i) in pancreatic beta-cells loaded with fura 2. This increase consisted of an early transient followed by a second, slower, rise. The [Ca2+]i transient was dependent on extracellular Ca2+ and disappeared on treatment with nimodipine. The reactive disulphide caused plasma membrane depolarization, as studied by the perforated-patch configuration of the patch-clamp technique. Hence membrane depolarization and opening of the L-type voltage-gated Ca2+ channels were responsible for the first transient in [Ca2+]i. The second slower increase in [Ca2+]i was prolonged but readily reversed by the disulphide-reducing agent 1,4-dithiothreitol. This increase in [Ca2+]i was not decreased by nimodipine or by omission of extracellular Ca2+, but was eliminated when the Ins(1,4,5)P3-sensitive Ca2+ pool was first depleted by carbachol. Ryanodine or its beta-alanyl analogue did not release Ca2+ from intracellular stores, and a high concentration of ryanodine did not inhibit Ca2+ release by 2,2'-DTDP. The disulphide compound suppressed glucose metabolism and decreased the mitochondrial inner-membrane potential. We conclude that thiol oxidation by 2,2'-DTDP affects Ca2+ homeostasis in beta-cells by multiple mechanisms. However, unlike the situation in muscle, in beta-cells 2,2'-DTDP releases Ca2+ from intracellular pools by mechanisms that do not involve activation of ryanodine receptors. Instead, in these cells the Ins(1,4,5)P3-sensitive intracellular Ca2+ store comprises an alternative target for the Ca(2+)-mobilizing action of the reactive disulphide compound.
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| 40. |
- Larsson, Arvid, 1979-, et al.
(författare)
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Charge state control of single InAs/GaAs quantum dots by means of an external magnetic field
- 2008
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Ingår i: in PHYSICS OF SEMICONDUCTORS, vol 1199. - : AIP. - 9780735407367 ; , s. 297-298
-
Konferensbidrag (refereegranskat)abstract
- Individual InAs/GaAs quantum dots (QDs) are studied with micro-photoluminescence in the presence of an applied external magnetic field. Attention is focused on the redistribution between the spectral lines of a single QD observed at increased external magnetic field when the magnetic field is applied parallel to the growth direction (Faraday geometry). The effect is shown to be transport related as the electron drift velocity in the QD-plane is decreased by the applied magnetic field and this affects the probability for electron capture into the QD.
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| 41. |
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| 42. |
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| 43. |
- Larsson, Arvid, et al.
(författare)
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Magnetic field enabled charge state control of single InAs/GaAs quantum dots
- 2009
-
Ingår i: 2009 9th IEEE Conference on Nanotechnology, IEEE NANO 2009. ; , s. 510-512
-
Konferensbidrag (refereegranskat)abstract
- Micro-photoluminescence in the presence of an external magnetic field is employed to study individual InAs/GaAs quantum dots (QDs). By varying the strength of the applied magnetic field, the charge state of the QD is tuned from a double negatively charged exciton to a neutral exciton. This effect is shown to be related to carrier transport in the QD-plane prior to capture into the QD. The temperature dependence of the tuning effect is discussed. © 2009 IEEE NANO Organizers.
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| 44. |
- Larsson, Anders, et al.
(författare)
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Peroxidase labelling of chicken anti-bodies
- 1999
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Ingår i: Food and Agricultural Immunology. - : Informa UK Limited. - 0954-0105 .- 1465-3443. ; 11:1, s. 43-49
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Tidskriftsartikel (refereegranskat)abstract
- Chicken antibodies have several advantages over mammalian antibodies due to the phylogenetical differences between birds and mammals, resulting in an increased sensitivity and a decreased background in many immunological assays. So far, there has been a very limited use of avian antibodies. This is probably partly due to tradition but also because there are very few optimized methods for the labelling of chicken antibodies. We report upon the suitable conditions for peroxidase-labelling of chicken antibodies with a modified periodate method.
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| 45. |
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| 46. |
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| 47. |
- Larsson-Kråik, Per-Olof, et al.
(författare)
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Pressure fluctuations as grease soaps pass through an EHL contact
- 2000
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Ingår i: Tribology International. - 0301-679X .- 1879-2464. ; 33:3-4, s. 211-216
-
Tidskriftsartikel (refereegranskat)abstract
- Soap lumps entering a grease-lubricated elastohydrodynamic lubrication (EHL) contact were traced as they passed through the contact by using optical interferometry in a standard Ball & Disc apparatus and a high-speed video camera with light enhancer. One specific soap lump could be traced when it was passing through the contact and sharp images of the passing lump could be captured. This paper presents a combined experimental and numerical approach to determine what is happening when such lumps pass through the contact. From the fringe pattern, obtained by optical interferometry, a film thickness map is created by using image processing. This is done for every time step (1 ms) as the lump is passing through the contact. These maps serve as input to a numerical computation of the pressure by assuming elastic deformation theory. Consequently, no assumptions about the rheological behaviour of the grease have to be made. Two greases were studied, based on the same synthetic poly-α-olefin but thickened with Li-12-OH and Li-complex respectively. It is seen that the soap thickened lumps can cause deep elastic indentations accompanied by large pressure fluctuations. The pressure level will in some cases be more than doubled due to lumps entering the contact region. The effects on noise level and operational life are also discussed.
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| 48. |
- Larsson, L. Arvid, et al.
(författare)
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Temperature and Magnetic Field Effects on the Transport Controlled Charge State of a Single Quantum Dot
- 2010
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Ingår i: NANOSCALE RESEARCH LETTERS. - : Springer Science Business Media. - 1931-7573 .- 1556-276X. ; 5:7, s. 1150-1155
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Tidskriftsartikel (refereegranskat)abstract
- Individual InAs/GaAs quantum dots are studied by micro-photoluminescence. By varying the strength of an applied external magnetic field and/or the temperature, it is demonstrated that the charge state of a single quantum dot can be tuned. This tuning effect is shown to be related to the in-plane electron and hole transport, prior to capture into the quantum dot, since the photo-excited carriers are primarily generated in the barrier.
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| 49. |
- Larsson, Per, et al.
(författare)
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Ecology, evolution, and management strategies of northern pike populations in the Baltic Sea
- 2015
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Ingår i: Ambio. - : Springer Science and Business Media LLC. - 0044-7447 .- 1654-7209. ; 44:Supplement 3, s. S451-S461
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Forskningsöversikt (refereegranskat)abstract
- Baltic Sea populations of the northern pike (Esox lucius) have declined since the 1990s, and they face additional challenges due to ongoing climate change. Pike in the Baltic Sea spawn either in coastal bays or in freshwater streams and wetlands. Pike recruited in freshwater have been found to make up about 50 % of coastal pike stocks and to show natal homing, thus limiting gene flow among closely located spawning sites. Due to natal homing, sub-populations appear to be locally adapted to their freshwater recruitment environments. Management actions should therefore not involve mixing of individuals originating from different sub-populations. We offer two suggestions complying with this advice: (i) productivity of extant freshwater spawning populations can be boosted by modifying wetlands such that they promote spawning and recruitment; and (ii) new sub-populations that spawn in brackish water can potentially be created by transferring fry and imprinting them on seemingly suitable spawning environments.
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| 50. |
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