| 1. |
- Lu, Lili, et al.
(författare)
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D-Glucose, forskolin and cytochalasin B affinities for the glucose transporter Glut1. Study of pH and reconstitution effects by biomembrane affinity chromatography
- 1997
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Ingår i: Journal of Chromatography A. - 0021-9673 .- 1873-3778. ; 776:1, s. 81-86
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Tidskriftsartikel (refereegranskat)abstract
- The affinities of D-glucose and the transport inhibitors, forskolin and cytochalasin B (CB), for Glut1 were studied by frontal affinity chromatography at pH 5-10 on sterically immobilized proteoliposomes with reconstituted human red cell glucose transporter Glut1. The affinity of D-glucose for Glut1 became slightly weaker as the pH was increased. The inhibitor affinities decreased and became immeasurably weak above pH 9. At pH 7.4, the dissociation constants were 44 mM for glucose, 1.8 microM for forskolin and 72 nM for CB. The affinities of these solutes for Glut1 in red cell membrane vesicles and particularly for Glut1 in red cells were higher, as shown by chromatographic analyses.
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| 2. |
- Lundqvist, Andreas
(författare)
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Chromatographic characterization of the human red cell glucose transporter Glut1 in the cells, in membrane vesicles and in proteoliposomes
- 1999
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- The human glucose transporter Glut1 is used by many cells, especially red blood cells andbrain cell, to take up glucose and other necessary metabolites. Gentle chromatographic methods can be applied for analyses of Glut1 activities in lipid environments similar to the native one. For this purpose, methods for immobilization of cells, cytoskeleton-depleted red cell membrane vesicles and proteoliposomes in chromatographic gel media have been developed and refined. The vesicles and proteoliposomes were immobilized by freeze-thaw-induced fusion in dextran-grafted agarose gel beads (Superdex 200). The sheltered environment in microcavities kept the Glut1 active for repeated analyses over time periods up to three months at room temperature.Frontal affinity chromatography, Hummel and Dreyer analyses and centrifugation methods revealed that the Glut1 affinities for inhibitors and D-glucose were highest in the cells andbecame successively lower upon cytoskeleton-depletion and subsequent solubilization andreconstitution. The affinity for D-glucose was higher at 37°C than at lower temperatures and varied with the pH. The cytochalasin-B binding characteristics of Glut1 changed upon reconstitution and, in the case of Glut1 in membrane vesicles, also upon immobilization. Glut1 in free membrane vesicles bound one cytochalasin-B molecule per monomer at saturation, whereas this ratio was halved upon immobilization of the vesicles to become equal to the ratio for Glut1 in proteoliposomes.
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| 3. |
- Lundqvist, Andreas, et al.
(författare)
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Frontal affinity chromatographic analysis of membrane protein reconstitution
- 1997
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Ingår i: Materials science & engineering. C, biomimetic materials, sensors and systems. - 0928-4931 .- 1873-0191. ; 4:4, s. 221-226
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Tidskriftsartikel (refereegranskat)abstract
- The human red cell glucose transporter Glut1 was solubilized with octaoxyethylene n-dodecyl ether (low critical micelle concentration (CMC)), purified, mixed with egg phospholipids and cholate, and reconstituted by gel filtration on Superdex 75. Free protepliposomes showed relatively high D-glucose transport activity. Frontal affinity chromatographic analysis with the proteoliposomes sterically immobilized in Superdex 200 gel beads revealed that the number of operative cytochalasin B (CB) binding sites increased during the first days of chromatographic runs to become the same as with 1-O-n-octyl β-d-glucopyranoside (high CMC) as solubilizer and Sephadex G-50 as gel filtration medium. The average number of sites per Glut1 monomer was 0.32 ± 0.02. The average Kd for CB was 66 ± 3 nM at 150 mM NaCl, similarly as for Glut1 in membrane vesicles, whereas the affinity of d-glucose for reconstituted Glut1 was lower (Kd = 44 ± 3 mM) than for membranous Glut1 (Kd = 15 ± 5 mM). Two theoretical treatments of affinity chromatographic data gave the same values in agreement with competitive and monovalent interactions.
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| 4. |
- Lundqvist, Björn, et al.
(författare)
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Empirical scaling of the vortex glass line above 1T for high-T(c) superconductors of varying anisotropy
- 1998
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Ingår i: Physical Review B. Condensed Matter and Materials Physics. - 1098-0121 .- 1550-235X. ; 57:22, s. 14064-14067
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Tidskriftsartikel (refereegranskat)abstract
- The resistive transition into a glassy vortex state in oxygen-deficient YBa(2)CU(3)O(7-delta) twinned single crystals of varying anisotropy gamma (8.7 less than or equal to gamma less than or equal to 35) has been studied with an applied magnetic field along the crystallographic c axis. For B greater than or similar to 1T, the glass. line is well described by the empirical relation B(g)=B(o)[(1 -T/T(c))/(T/T(c))](alpha), where alpha approximate to 1 and B(o) approximate to 1.85 Phi(o)/(gamma d)(2). The successful fit to this relation both below and above an alleged crossover in the solid vortex state has important consequences for the H-T phase diagram of high-temperature superconductors.
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| 5. |
- Lundqvist, Björn, et al.
(författare)
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Vortex dynamics in oxygen deficient single crystals of YBa2Cu3O7-delta
- 1997
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Ingår i: Physica. C, Superconductivity. - 0921-4534 .- 1873-2143. ; 282, s. 1959-1960
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Tidskriftsartikel (refereegranskat)abstract
- In YBa2Cu3O7-delta (YBCO), oxygen deficiencies in the CuO chains change the coupling between the charge carriers in adjacent superconducting CuO2 planes and thereby the electrical anisotropy, gamma=(m(c)/m(ab))(1/2). Such crystals therefore provide a simple test system for systematic studies of the influence of anisotropy on vortex dynamics. We have studied the vortex glass transition of YBCO single crystals with delta in the range of 0.07 to 0.27, corresponding to gamma between 9 and 18, for magnetic fields 0
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| 6. |
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