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  • 11
    Electronic Resource
    Electronic Resource
    Semi-quantitative assessment of anti-insulin total IgG and IgG sub-classes in insulin-immunized patients using a highly sensitive immunochemical micromethod (1986)
    Springer
    Diabetologia 29 (1986), S. 720-726 
    Details
    ISSN: 1432-0428
    Keywords: Anti-insulin ; IgG sub-classes ; monoclonal antibodies ; enzyme linked immunosorbant assay
    Source: Springer Online Journal Archives 1860-2000
    Topics: Medicine
    Notes: Summary An immunochemical micromethod was designed to estimate total IgG and IgG sub-classes of anti-insulin antibodies in immunized diabetic patients. Insulin, immobilized on a solid phase, was allowed to react with serum samples containing anti-insulin antibodies. Bound anti-insulin IgG interacted with mouse monoclonal antibodies specific for total IgG or for each IgG isotype. The fixation of mouse monoclonal antibody was subsequently detected using a horseradish peroxidase-conjugated rabbit anti-mouse IgG in the presence of a chromogenic substrate. The test was standardized by an immunocapture assay utilizing coated rabbit anti-human IgG and known concentrations of purified human myelomatous proteins of each sub-class. Results of anti-insulin IgG and anti-insulin IgG sub-classes assay could therefore be expressed in ng equivalent myelomatous proteins per ml of serum. Analysis of serum samples from 24 insulin-immunized diabetic patients revealed a quasi absence of IgG2 anti-insulin antibodies and an increase of the relative abundance of the other three anti-insulin IgG isotypes. In our series, anti-insulin IgG1 was predominant, followed by IgG3 (in 17/24 patients) or IgG4 (in 7/24). Insulin immunization was deduced to be of polyclonal nature, the isotype pattern of which is not representative of the relative proportion of IgG sub-classes in whole normal serum.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00870282
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  • 12
    Electronic Resource
    Electronic Resource
    Advantages and pitfalls of radioimmune and enzyme linked immunosorbent assays of insulin antibodies (1988)
    Springer
    Diabetologia 31 (1988), S. 694-702 
    Details
    ISSN: 1432-0428
    Keywords: Radioimmune assay ; enzyme linked immunosorbent assay ; insulin antibodies
    Source: Springer Online Journal Archives 1860-2000
    Topics: Medicine
    Notes: Summary Human sera were tested for insulin antibodies by fluid and solid phase assays. Radioimmune titres determined with 125-I Tyr A14 insulin were not correlated with those obtained using insulin coated microplates and enzyme linked immunodetection (n=60). Several reasons for this lack of correlation were found. Iodine substitution on the A14 residue of insulin may significantly alter the avidity of some insulin antibodies for their ligand; hence, disclosing a heretofore unsuspected pitfall for antibody determination by radio-immunoassay. Specificity for bovine insulin was easily demonstrable in fluid phase by comparing the binding of monoiodinated bovine, porcine and human insulin. By contrast, in solid phase assay, titres obtained with microplates coated with bovine or human insulin were almost equal, regardless of the serum specificity for bovine insulin. This lack of specificity of the solid phase assay is not due to denaturation or unavailability of the bovine specific epitope because: bovine specificity could be demonstrated by competitive assay, after preincubation of the serum with insulin of the different species; and, coating with crosslinked insulin dimers or oligomers instead of monomers did not unmask bovine specificity. It is concluded that radioimmune methods are best suited to study specificity but may be biased by the presence of the radioiodine label whereas solid phase assay detects low avidity antibodies with great efficiency but is less appropriate to study specificity.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00278754
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  • 13
    Electronic Resource
    Electronic Resource
    Time-resolved X-ray scattering study of actin polymerization from profilactin (1985)
    Springer
    European biophysics journal 13 (1985), S. 99-108 
    Details
    ISSN: 1432-1017
    Keywords: Profilactin ; actin polymerization ; X-ray scattering
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Physics
    Notes: Abstract The polymerization of actin in solutions of purified calf spleen actin or profilactin (1–10 mg·ml-1) was followed by synchrotron radiation X-ray solution scattering. At the concentration used, polymerization of actin from profilactin or actin occurs without any lag phase. It is shown by a combination of solution scattering, model calculations and electron microscopy that contrary to the conclusions from previous viscometry studies, filaments form without any lag phase in profilactin solution but aggregate in bundles or networks. This phenomenon is independent of the method used to induce polymerization: slow temperature increase, temperature jump in the presence of polymerizing salts or fast mixing with salt. This aggregation explains the lower final viscosity levels, as compared to actin solutions, observed during the polymerization of actin from profilactin.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00256530
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  • 14
    Electronic Resource
    Electronic Resource
    The superstructure of chromatin and its condensation mechanism (1987)
    Springer
    European biophysics journal 15 (1987), S. 133-140 
    Details
    ISSN: 1432-1017
    Keywords: X-ray solution scattering ; synchrotron radiation ; chicken erythrocyte chromatin ; rat liver chromatin ; micrococcal nuclease
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Physics
    Notes: Abstract Changes in the structure of chicken erythrocyte chromatin fibres at low ionic strength resulting from enzymatic digestion, thermal denaturation and binding of Netropsin and Distamycin were monitored by synchrotron X-ray solution scattering. Digestion with micrococcal nuclease confirms the previous assignment of the 0.05 nm-1 band to an interference between nucleosomes with an average distance of 23 nm. The results of thermal denaturation indicate that above 40°C there is a progressive increase of the internucleosomal distance and that above 60°C the characteristic structure of the chromatin fibre is destroyed. Binding of Netropsin and Distamycin also results in an increase of the internucleosomal distance which can be estimated to correspond to about 0.2 nm/mol.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00263677
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  • 15
    Electronic Resource
    Electronic Resource
    Kinetic study of the self-assembly of brome mosaic virus capsid (1987)
    Springer
    European biophysics journal 15 (1987), S. 159-168 
    Details
    ISSN: 1432-1017
    Keywords: Plant virus ; morphogenesis ; kinetic ; X-rays ; light scattering
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Physics
    Notes: Abstract The protein of brome mosaic virus can self assemble in-vitro to form empty capsids. In the absence of RNA at pH=7 and 0.5 M KCl there is a dynamic equilibrium between monomers and oligomers. At pH=5 the protein assembles into empty capsids. The kinetics of this assembly, triggered by pH jump from neutral to acidic pH, was investigated by X-ray and light scattering. Cryoelectron microscopy observations suggested that reconstitution is achieved by progressive incorporation of small building units in a spherical shell. This hypothesis has been tested by the analysis of the scattering data in terms of four classes of incomplete capsids represented as spherical shells with holes of different sizes. The time dependence of the population of each class was determined by a least squares analysis of the experimental data. Although the basic polymerizing unit has not been uniquely characterized, the results are compatible with a dimer for this species. The characteristic times for capsid assembly are found to vary as the inverse of the square of the concentration.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00263680
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  • 16
    Electronic Resource
    Electronic Resource
    The superstructure of chromatin and its condensation mechanism (1989)
    Springer
    European biophysics journal 17 (1989), S. 245-255 
    Details
    ISSN: 1432-1017
    Keywords: X-ray solution scattering ; synchrotron radiation ; electric dichroism ; chicken erythrocyte chromatin
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Physics
    Notes: Abstract Electric dichroism and X-ray scattering measurements on solutions of uncondensed and condensed chicken erythrocyte chromatin were interpreted on the basis of model calculations. Information about the state of uncondensed fibers in the conditions of electric dichroism measurements was obtained from scattering patterns recorded as a function of pH, in the presence of spermine and at very low monovalent cation concentrations. Electric dichroism measurements on a complex of uncondensed chromatin with methylene blue were made to determine the contribution of the linker and of the nucleosomes to the total dichroism. A new approach to calculate the dichroism from realistic structural models, which also yields other structural parameters (radius of gyration, radius of gyration of the cross-section, mass per unit length) was used. Only a restricted range of structures is simultaneously compatible with all experimental results. Further, it is shown that previous interpretations of dichroism measurements on chromatin were in contradiction with X-ray scattering data and failed to take into account the distribution of orientation of the nucleosomes in the fibers. When this is done, it is found that the linker DNA in chicken erythrocyte and sea urchin chromatin must run nearly perpendicularly to the fibre axis. Taken together with the dependence of the fibre diameter on the linker length, these results provede the strongest evidence hitherto available for a model in which the linker crosses the central part of the fibre.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00254282
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  • 17
    Electronic Resource
    Electronic Resource
    The superstructure of chromatin and its condensation mechanism (1986)
    Springer
    European biophysics journal 13 (1986), S. 175-185 
    Details
    ISSN: 1432-1017
    Keywords: Chromatin superstructure ; chromatin condensation
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Physics
    Notes: Abstract Model calculations on the superstructure of uncondensed and condensed chromatin are presented. It is found that agreement between the calculated X-ray solution scattering patterns and the experimental observations can be reached with the assumptions that: a) The uncondensed chromatin fibre in solution has a helix-like structure, with a pitch of ca. 33.0 nm, a helical diameter of ca. 20.0 nm and 2.75–3.25 nucleosomes per turn. b) The most condensed state of the chromatin fibre in solution is best represented by a helix-like structure with ca. 2.56 nucleosomes per turn, a pitch of ca. 3.0 nm and a helical diameter of ca. 27.0 nm.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00542561
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  • 18
    Electronic Resource
    Electronic Resource
    The superstructure of chromatin and its condensation mechanism (1986)
    Springer
    European biophysics journal 13 (1986), S. 157-173 
    Details
    ISSN: 1432-1017
    Keywords: Synchroton radiation ; chromatin superstructure ; chromatin condensation
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Physics
    Notes: Abstract Synchroton radiation X-ray scattering experiments have been performed on chicken erythrocyte chromatin fibres over a wide range of ionic conditions and on various states of the fibres (i.e. “native” in solution in gels and in whole nuclei; chromatin depleted of the H1 (H5) histones and chromatin with bound ethidium bromide). A correlation between the results obtained with the various chromatin preparations provides evidence for a model according to which at low ionic strength the chromatin fibre already possesses a helical superstructure, with a diameter comparable to that of condensed chromatin, held together by the H1 (H5) histone. The most significant structural modification undergone upon an increase of the ionic strength is a reduction of the helix pitch, this leads to condensation in a manner similar to the folding of an accordion. The details of this process depend on whether monovalent or divalent cations are used to raise the ionic strength, the latter producing a much higher degree of condensation. Measurements of the relative increase of the mass per unit length indicate that the most condensed state is a helical structure with a pitch around 3.0–4.0 nm. In this paper we give a detailed presentation of the experimental evidence obtained from static and time-resolved scattering experiments, which led to this model.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00542560
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  • 19
    Electronic Resource
    Electronic Resource
    The superstructure of chromatin and its condensation mechanism (1987)
    Springer
    European biophysics journal 14 (1987), S. 307-319 
    Details
    ISSN: 1432-1017
    Keywords: Chromatin ; synchrotron radiation ; ultracentrifugation ; viscosity ; modelling
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Physics
    Notes: Abstract Solutions of rat liver and chicken erythrocyte chromatin at different ionic strngths were characterized by synchrotron X-ray solution scattering, ultracentrifugation, density and viscosity measurements. Previous observations on nuclei were extended to rat liver, calf thymus and yeast nuclei. It is shown that with monovalent cations condensation is independent of the nature of the cation whereas with divalent cations there are significant differences related to the preference of base binding over phosphate binding. The consistency of hydrodynamic and scattering results confirm the view that chromatin in solution at low ionic strength has a helix-like superstructure. A survey of X-ray and neutron scattering results in the literature shows that previous interpretations, e.g. in terms of a 10 nm filament, are incompatible with the experimental data at low resolution.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00254896
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  • 20
    Electronic Resource
    Electronic Resource
    The superstructure of chromatin and its condensation mechanism (1988)
    Springer
    European biophysics journal 16 (1988), S. 177-185 
    Details
    ISSN: 1432-1017
    Keywords: X-ray solution scattering ; synchrotron radiation ; sea urchin chromatin ; solubility ; condensation ; electric dichroism
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Physics
    Notes: Abstract Comparison between the internucleosomal distance found by X-ray solution scattering for chicken erythrocyte (23 nm) and sea urchin (30 nm) chromatin indicates that this distance is proportional to the linker length. The diameter of the condensed sea urchin chromatin fibers is about 45 nm which is significantly larger than in chicken erythrocyte chromatin (35 nm). Trivalent cations (Gd, Tb, Cr) and the polyamines spermine and spermidine were found to induce compaction at much lower concentrations than the divalent cations but Gd, Tb and Cr induce aggregation before full compaction of the fibers. The influence of hydrogen bonding is illustrated by comparison of the effects of NaCl, ammonium chloride and alkylammonium chlorides on condensation. Solubility experiments indicate that there is a nearly linear dependence of the Mg-- concentration at which precipitation occures on chromatin concentration and confirm the differences between cations observed by X-ray scattering. The chicken erythrocyte chromatin samples were further characterized by their reduced electric dichroism. The values found are consistent with the model derived from X-ray scattering and are compared with those reported in the literature.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00261903
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