| 1. |
- Graslund, A., et al.
(author)
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DYNAMICS OF BENZO A PYRENE DIOL EPOXIDE ADDUCTS IN POLY(DG-DC) . (DG-DC) STUDIED BY SYNCHROTRON EXCITED FLUORESCENCE POLARIZATION ANISOTROPY DECAY
- 1992
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In: Biophysical Chemistry. - : Elsevier BV. - 1873-4200 .- 0301-4622. ; 44:1, s. 21-28
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Journal article (peer-reviewed)abstract
- Time-resolved fluorescence studies have been performed on (+)-anti-7,8-dihydrodiol-9,10-epoxy-benzo[a]pyrene adducts in double-stranded poly(dG-dC) . (dG-dC). Part of the adduct population gives rise to excimer fluorescence. The heterogeneous fluorescence emission decay curves at 22-degrees-C could be resolved into three components with lifetimes: 0.4 ns, 3 ns and 24 ns for the total fluorescence (monomer and excimer emission), and 0.5 ns, 5 ns and 24 ns, respectively, for excimer emission alone. The relative amplitudes for the longer lifetimes were larger for the pure excimer population than for the mixed population. The fluorescence polarization anisotropy decay curves were resolved into two components of rotational correlation times: 0.4 ns and 25 ns for the total fluorescence and 0.3 ns and 33 ns for the excimer fluorescence. We interpret the two rotational correlation times to correspond to local motion of the adduct and segmental motion of the polynucleotide, respectively.
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| 2. |
- Mörgelin, Matthias, et al.
(author)
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The cartilage proteoglycan aggregate: assembly through combined protein-carbohydrate and protein-protein interactions
- 1994
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In: Biophysical Chemistry. - : Elsevier BV. - 1873-4200 .- 0301-4622. ; 50:1-2, s. 113-128
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Journal article (peer-reviewed)abstract
- In vitro reassembled aggregates of cartilage proteoglycan (aggrecan) were studied by glycerol spraying/rotary shadowing electron microscopy and compared to the corresponding native (i.e. never dissociated) structures. In both cases a tightly packed central filament structure was observed consisting of the hyaluronate binding region (HABR) of the proteoglycan, link protein (LP) and hyaluronate (HA). This differs from earlier results where a discontinuous central filament structure was seen after spreading proteoglycan aggregates at a water/air interphase. Binding of isolated HABR to HA is random but upon addition of link protein a clustering of the HA-binding proteins is observed, indicating a cooperativity. In a fully saturated aggregate the HA is covered by a continuous protein shell consisting of HABR and LP. When added in amounts below saturation HABR and LP bind to the HA in clusters which are interrupted by free strands of HA. The proteoglycan aggregate is thus an example for a structure where a polysaccharide forms a template for a supramolecular assembly largely stabilized by protein-protein interactions.
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| 3. |
- Nordén, Bengt, 1945, et al.
(author)
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High-sensitivity linear dichroism as a tool for equilibrium analysis in biochemistry- stability constant of DNA-ethidiumbromide complex
- 1976
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In: Biophysical Chemistry. - : Elsevier BV. - 1873-4200 .- 0301-4622. ; 4:2, s. 191-198
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Journal article (peer-reviewed)abstract
- A stoichiometrical application of a sensitive method for linear dichroism (LD) detection is suggested for biochemical purposes. The complex formation between a binding site on a polynucleotide and a ligand may be studied with high precision if the following conditions are fulfilled: (1) The polymer can be given a fixed degree of orientation. (2) The site has a specific orientation with respect to the orientation axis of the polymer (e.g., intercalation). (3) The ligand has an anisotropic optical absorption property.The method was applied to studying the complex between DNA and ethidiumbromide, which was detected by LD with precision of ± 0.5 × 10−7 M in a 4 × 10−4 M DNA solution, i.e., 0.1% occupation of the total site concentration can be detected. The complsxation could be explained by a single type of site (n = 0.14 ± 0.01 sites per nucleotide residue) and a stability constant K1 = (2.5 ± 1) × 105 M−1 at 0.2 M ionic strength.From the specific LD an average angle 60° was concluded between the helix axis and the long axis of the ethidiumbromide molecule.This value formally contradicts the Watson-Crick model or the intercalation model but may be explained by extension and deformation effects on the xhain by the flow.
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| 4. |
- Nordén, Bengt, 1945, et al.
(author)
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Linear dichroism studies of binding site structures in solution: Complexes between DNA and basic arylmethane dyes
- 1978
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In: Biophysical Chemistry. - : Elsevier BV. - 1873-4200 .- 0301-4622. ; 8:1, s. 1-15
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Journal article (peer-reviewed)abstract
- The interaction between B-form DNA and twelve cationic triaryl-methane dyes was studied with respect lo optical properties and stabilities, using linear dichroism (LD) and aqueous two-phase partition techniques. Monovalent dyes derived from crystal violet as a rule form a single strong complex (K1 ca 105 M−1; site density per nucleotide base n1 ca 0.1 at 0.1M ionic strength) in which the plane of the dye is at an angle of less than 50° to the local DNA helix axis. The complex with fuchsin is weaker (104M−1) but can be explained by a similar orientation. For some of the dyes (those with pseudo-C2v symmetry) XXXre angular orientations of two molecule-fixed axes can be obtained. For the divalent methyl green a second complex appears to be formed at low ionic strength. Methyl green (and to some extent 2-thiophene green and malachite green) show exciton splitting in the LD spectrum and circular dichroism assignable to exciton coupling between transition dipoles roughly parallel to the helical strands, indicating a dye-dye interaction. Tne optical data, supported by fitting experiments with space-filling models, suggests a general structure for the binding site. The dye is not intercalated but is bound to exposed hydrophobic regions in the major groove. The ligand is in part (the charged amino groups) in contact with the phosphoribose chain but its main surface lies against the hydrophobic base-pair stack. For a diphenylmethane dye, Michler's hydrol blue, a perpendicular orientation was observed, possibly due to intercaiation.
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| 5. |
- Nordén, Bengt, 1945, et al.
(author)
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Optical studies on complexes between DNA and pseudoisocyanine
- 1976
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In: Biophysical Chemistry. - : Elsevier BV. - 1873-4200 .- 0301-4622. ; 6:1, s. 31-45
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Journal article (peer-reviewed)abstract
- Linear dichroism (LD) results when pseudoisocyanine = PIC (1, 1-diethyl-2,2'-cyanine iodide) binds to flow-oriented DNA. LD may be used to follow the complexation both stoichiometrically and structurally, since when specified to unit complex concentration LD provides a measure of the average orientation of the absorbing transition dipole.Two different types of complexes can be distinguished: I. One strong, ionic-strength insensitive complex with monomeric PIC with an orientation indicating intercalation. II. Several weaker complexes of electrostatic nature (only observed at I
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| 6. |
- Nordén, Bengt, 1945
(author)
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Structural evidence on DNA carcinogen interactions: N-acetoxy-N-2acetylaminofluorene binding to DNA
- 1978
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In: Biophysical Chemistry. - : Elsevier BV. - 1873-4200 .- 0301-4622. ; 8:4, s. 385-391
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Journal article (peer-reviewed)abstract
- Linear dichroism (LD) gives useful information on the interaction between DNA and the directly acting carcinogen N-acetoxy-N-2-acetylaminofluorene (AAAF). In 50% methanol solvent with low ionic strength only a weak complex (van der Waals) appears. However, above 40° C strand separation takes place and a covalent aminofluorene complex forms. After renaturation a characteristic positive LD.band is observed at 306 nm. The average angular orientation of the longaxis of the fluorene moiety (47° to the local helix axis) is inconsistent with intercalation- It can be explained for instance by a free rotation around a C(DNA)-N (aminofluorene) bond or by a major groove site. The occupation density was 1–2 aminofluorene residues per 100 bases. With native DNA, AAAF slowly forms a covalent complex which has a negative LD at 307 nm. The orientation (70–90° ) is consistent with steric direction by the strand.
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| 7. |
- Bergstrand, Nill, et al.
(author)
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Interactions between pH-sensitive liposomes and model membranes
- 2003
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In: Biophysical Chemistry. - 0301-4622 .- 1873-4200. ; 104:1, s. 361-379
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Journal article (peer-reviewed)abstract
- The structure and dynamics of two different pH-sensitive liposome systems were investigated by means of cryo-transmission electron microscopy and different photophysical techniques. Both systems consisted of dioleoylphosphatidylethanolamine (DOPE) and contained either oleic acid (OA) or a novel acid-labile polyethylene glycol-conjugated lipid (DHCho-MPEG5000) as stabiliser. Proton induced leakage, lipid mixing and structural changes were studied in the absence and presence of EPC liposomes, as well as in the presence of liposomes designed to model the endosome membrane. Neither DHCho-MPEG5000- nor OA-stabilised liposomes showed any tendency for fusion with pure EPC liposomes or endosome-like liposomes composed of EPC/DOPE/SM/Cho (40/20/6/34 mol.%). Our investigations showed, however, that incorporation of lipids from the pH-sensitive liposomes into the endosome membrane may lead to increased permeability and formation of non-lamellar structures. Taken together the results suggest that the observed ability of DOPE-containing liposomes to mediate cytoplasmic delivery of hydrophilic molecules cannot be explained by a mechanism based on a direct, and non-leaky, fusion between the liposome and endosome membranes. A mechanism involving destabilisation of the endosome membrane due to incorporation of DOPE, seems more plausible.
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| 8. |
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| 9. |
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| 10. |
- Huber, M., et al.
(author)
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Phase memory relaxation times of spin labels in human carbonic anhydrase II : Pulsed EPR to determine spin label location
- 2001
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In: Biophysical Chemistry. - 0301-4622 .- 1873-4200. ; 94:3, s. 245-256
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Journal article (peer-reviewed)abstract
- Phase memory relaxation times (TM or T2) of spin labels in human carbonic anhydrase II (HCA II) are reported. Spin labels (N-(1-oxyl-2,2,5,5-tetramethyl-3-pyrrolidinyl)iodoacetamide, IPSL) were introduced at cysteines, by site-directed mutagenesis at seven different positions in the protein. By two pulse electron paramagnetic resonance (EPR), electron spin echo decays at 45 K are measured and fitted by stretched exponentials, resulting in relaxation parameters TM and x. TM values of seven positions are between 1.6 ╡s for the most buried residue (L79C) and 4.7 ╡s for a residue at the protein surface (W245C). In deuteriated buffer, longer TM are found for all but the most buried residues (L79C and W97C), and electron spin echo envelop modulation (ESEEM) of deuterium nuclei is observed. Different deuterium ESEEM patterns for W95C and W16C (surface residue) indicate differences in the local water concentration, or accessibility, of the spin label by deuterium. We propose TM as a parameter to determine the spin label location in proteins. Furthermore, these systems are interesting for studying the pertaining relaxation mechanism. ⌐ 2001 Elsevier Science B.V. All rights reserved.
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