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Biomedical subjects

V A Bloomfield

Publications and source records attributed to V A Bloomfield.

At least 91 records · Page 5Linked to original sources
PubMed1983

Chain flexibility and hydrodynamics of the B and Z forms of poly(dG-dC).poly(dG-dC).

The solution properties of the B and Z forms of poly(dG-dC).poly(dG-dC) have been measured by static and dynamic laser light scattering. The radius of gyration, persistence length, translational and segmental diffusion coefficients, and the Rouse-Zimm parameters have been evaluated. The persistence length of the Z form determined at 3 M NaCl is about 200 nm compared to 84 and 61 nm respectively for the B forms of poly(dG-dC).poly(dG-dC), and calf thymus DNA, both determined at 0.1 M NaCl. The data on persistence length, diffusion coefficients and the Rouse-Zimm parameters indicate a large increase in the chain stiffness of Z DNA compared to the B form. These results are opposite to the ionic strength effects on random sequence native DNAs, for which the flexibility increases with ionic strength and levels off at about 1 M NaCl.

Animals↗
PubMed1982

Kinetic and hydrodynamic analysis of blood clotting factor V-membrane binding.

The kinetics and hydrodynamic properties of factor V-membrane interaction were characterized. Factor V bound to membranes containing acidic phospholipids with a high collisional efficiency. For membranes of 20% phosphatidyl-serine-80% phosphatidylcholine, an association rate constant of (1.13 +/- 0.10) X 10(8) M-1 s-1 was obtained. These membranes contained about 20 factor V binding sites per vesicle of 3.6 X 10(6) daltons. This association rate represented about a 30% collisional efficiency. Dissociation of factor V was measured by a fluorescence energy transfer method with a dissociation rate constant of 0.0055 s-1 at 10 degrees C. The equilibrium dissociation constant for binding to these membranes at 10 degrees C and 0.14 M ionic strength was 5 X 10(-11) M. Ionic strength, pH, calcium, and charge density in the membrane had large effects on the rate of factor V-membrane dissociation, indicating a strongly ionic interaction between protein and membrane. In contrast, the association rate was nearly insensitive to ionic strength. The membrane-binding properties were relatively unchanged after thrombin digestion of factor V or after long-term protein storage which resulted in loss of procoagulant activity. Other proteins of the prothrombinase reaction greatly decreased the rate of factor Va-membrane dissociation. At protein saturation, factor V increased the hydrodynamic radius of phospholipid vesicles by 11.4 nm. In contrast, factor Va increased the hydrodynamic vesicle radius by only about 5 nm. The mass of membrane-bound protein was comparable for both proteins.

Animals↗
PubMed1982

Subunit arrangement of cholera toxin in solution and bound to receptor-containing model membranes.

Quasi-elastic laser light scattering (QLS) is used to study the translational frictional properties of cholera toxin and its complex with ganglioside Gm1 receptor containing phospholipid vesicles. These properties are compared to theoretically calculated values for model structures composed of spherical subunits in order to assess the structural configuration of the toxin and its binding geometry on membrane surfaces. The structure for the toxin that best fits the experimental results consists of the five B subunits arranged radially about an elongated A subunit, which extends well above the plane of the B subunits. Binding of cholera toxin to Gm1-containing model membranes results in a complex in which the B subunits are absorbed on the surface while the A subunit penetrates the membrane bilayer.

Animals↗
PubMed1982

Cholera toxin mediated agglutination of ganglioside Gm1 containing phospholipid vesicles and Gm1-coated polystyrene spheres.

Quasi-elastic laser light scattering is used to examine the cholera toxin mediated agglutination of ganglioside GM1 containing phospholipid vesicles and Gm1-coated polystyrene spheres. We find that the ability of cholera toxin to agglutinate Gm1-containing phospholipid vesicles depends markedly on the lipid composition of the vesicle, with only those composed of short-chain lipids (C14, C16) being appreciably agglutinated. This is interpreted as due to poor mixing of these lipids with the longer chain gangliosides, resulting in lateral separation of the gangliosides in the membrane bilayer. A simple quantitative model, a modification of that developed by von Schulthess et al. [von Schulthess, G. K., Cohen, R. J., Sakato, N., & Benedek, G. B. (1976a) Immunochemistry 13, 955--962], is developed to describe these agglutination processes. Application of this model to the agglutination of Gm1-coated polystyrene spheres by cholera toxin allows an estimate of a minimum value of 4.5 x 10(4) M-1 for the association constant of cholera toxin for its initial Gm1 receptor.

Agglutination↗
PubMed1982

Higher order folding of two different classes of chromatin isolated from chicken erythrocyte nuclei. A light scattering study.

Bulk chromatin fragments were excised from chicken erythrocyte nuclei by digestion with micrococcal nuclease. Fractionation into S chromatin (soluble at physiological ionic strengths) and I chromatin (insoluble at physiological ionic strengths) was achieved by dialysis against buffers containing 0.15 M NaCl. The effects of NaCl concentration on the molecular dimensions of S and I chromatins were determined by dynamic and static light scattering. Series of fragment lengths were obtained by gel filtration of S and I chromatins under ionic conditions which lead to maximal intramolecular compaction. Hydrodynamic radii and radii of gyration were determined for fragment lengths ranging from 8 to 53 nucleosomes. These data are in excellent agreement with calculations for extended helical structures. Close-packed solenoidal or superbead structures are not compatible with these data. Comparisons of molecular dimensions derived from light scattering and electron microscopy indicate that considerable shrinkage of chromatin fragments can occur when common methods of sample preparation are used for microscopy.

Animals↗
PubMed1981

Effect of chymosin action on the hydrodynamic diameter of casein micelles.

Quasi-elastic light scattering shows an initial decrease of about 5 nm in the hydrodynamic radius of casein micelles after adding chymosin, assuming the decrease to be equal for all micelles. This is consistent with the hypothesis that casein micelles have a hairy outer layer that is partly made up of the caseino-macropeptide part of kappa casein.

Caseins↗
PubMed1981

Chicken erythrocyte nucleus contains two classes of chromatin that differ in micrococcal nuclease susceptibility and solubility at physiological ionic strength.

Inactive chromatin of the chicken erythrocyte nucleus is shown to consist of two distinct classes (I and S). I chromatin (approximately 60% of the total genome) is insoluble at greater than 0.1 M ionic strength whereas S chromatin (approximately 40% of the total genome) is soluble at all ionic strengths studied (0.01--0.3 M). These chromatins are released from nuclei upon digestion with micrococcal nuclease by two separate parallel processes that do not have a precursor--product relationship to each other. Isolated I-chromatin fragments show a progressive reduction in size from 250 to approximately 50 nucleosome equivalents with increasing digestion times at 0-2 degrees C. Prolonged digestion of nuclei at 37 degrees C results in conversion of I chromatin to mononucleosomes that are insoluble at greater than 30 mM NaCl. Isolated S-chromatin fragments show a constant size distribution, independent of digestion time, that peaks at approximately 35 nucleosome equivalents. Prolonged digestion of nuclei at 37 degrees C results in the conversion of S chromatin to mononucleosomes that are soluble at physiological ionic strength. Both I and S chromatins contain a full complement of histones with no nonhistone proteins.

Animals↗