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Biomedical subjects

V A Bloomfield

Publications and source records attributed to V A Bloomfield.

At least 127 records · Page 7Linked to original sources
PubMed1977

Structure of the prothrombin- and blood clotting factor X-membrane complexes.

The configuration of the prothrombin- and factor X-membrane complexes was investigated by the technique of quasielastic light scattering. It is concluded that the fragment 1 region of prothrombin is located at one end of the prothrombin molecule and that the membrane binding site is at the tip of the fragment 1 region. Prothrombin binds to the surface of the membrane with no detected penetration into the lipophilic region of the membrane. The remainder of the prothrombin molecule extends radially from the membrane surface with maximum protrusion into solution. Factor X also binds to the membrane at one end of the molecule and extends into solution. Based on the evidence presented here and in other communications [Nelsestuen, G. L., and Lim, T. K. (1977), Biochemistry 16, and Nelsestuen, G. L., and Broderius, M. (1977), Biochemistry 16 (respectively the first and second in a series of three papers in this issue)] a model for prothrombin-membrane interaction is given. Quasielastic light scattering appears to be a valuable new method for studying protein-membrane interactions.

Animals↗
PubMed1977

Hydrodynamic theory of swimming of flagellated microorganisms.

A theory of the type commonly used in polymer hydrodynamics is developed to calculate swimming properties of flagellated microorganisms. The overall shape of the particle is modeled as an array of spherical beads which act, at the same time, as frictional elements. The fluid velocity field is obtained as a function of the forces acting at each bead through Oseen-type, hydrodynamic interaction tensors. From the force and torque equilibrium conditions, such quantities as swimming velocity, angular velocity, and efficiency can be calculated. Application is made to a spherical body propelled by a helical flagellum. A recent theory by Lighthill, and earlier formulations based on tangential and normal frictional coefficients of a curved cylinder, CT and CN, are analyzed along with our theory. Although all the theories predict similar qualitative characteristics, such as optimal efficiency and the effect of fluid viscosity, they lead to rather different numerical values. In agreement with Lighthill, we found the formalisms based on CN and CT coefficients to be somewhat inaccurate, and head-flagellum interactions are shown to play an important role.

Flagella↗
PubMed1975

Hydrogen-tritium exchange kinetics of soybean trypsin inhibitor (Kunitz). Solvent accessibility in the folded conformation.

The hydrogen exchange kinetics of Kunitz soybean trypsin inhibitor (STI) has been studied at pH 2, 3, and 6.5. From the temperature dependence of proton exchange at low pH, THE CONTRIBUTION OF MAJOR, REVERSIBLE PROTEIN UNFOLDING To the hydrogen exchange kinetics has been determined. Exchange directly from the folded conformation is characterized by an apparent activation energy (E*app) of approximately 25 kcal/mol, close to that of the chemical exchange step. At pH 6.5 the protein is more temperature stable than at low pH, and exchange of all but congruent to 8 protons can be observed to exchange with E*app congruent to 27 kcal/mol. This implies that all but congruent to 8 protons are accessible to exchange with solvent in the solution structure of folded STI. Estimates can be made of the average number of water molecules per molecule of STI consistent with a solvent accessibility model of hydrogen exchange kinetics. These estimates indicate that very few water molecules within the protein matrix are necessary to explain the exchange data. Calculations are done for the STI hydrogen exchange kinetics at pH 3, 30 degrees, approximating STI structure by a sphere of radius = 18 A. These calculations indicate an average of congruent to 4 water molecules in the shell from 13 to 16 A. from the center of the molecule, while less than 1 water molecule is indicated in the innermost 13 A. These calculations also suggest that there are congruent to 190 water molecules associated with the outermost 1.5-2 A of the sphere. While these values are consistent with a hydrophobic region in the central protein matrix, they indicate more solvent accessibility in the outer 1/3 of the molecule than the static accessibility estimates made from X-ray coordinates. Our results suggest that any protein movements or fluctuations responsible for solvent accessibility in proton exchange processes are localized in the outer regions of the globular structure.

Binding Sites↗
PubMed1975

Structure and stability of casein micelles.

The structure and stability of casein micelles are determined in large measure by the amino acid sequences of the constituent alphas1-, beta-, and kappa- caseins. In this paper we review, and attempt to connect with sequence data where possible: (1) molecular weight, structure, and dissociation of casein micelles; (2) physical characteristics of monomeric caseins, especially the distrubition of charged and hydrophobic residues and the possible occurrence of helical regions; and (3) forces involved in association of monomers.

Amino Acid Sequence↗