Yoshinobu Izumi

Aggregation of bovine serum albumin upon cleavage of its disulfide bonds, studied by the time-resolved small-angle x-ray scattering technique with synchrotron radiation

A rapid mixing system of the stopped-flow type, used with small-angle X-ray scattering equipment using synchrotron radiation, is described. The process of aggregation of bovine serum albumin was traced with a time interval of 50 s, initiated upon cleavage of its disulfide bonds by reduction with dithiothreitol. The results indicate that a 218-fold molar excess of dithiothreitol over the number of moles of disulfide bonds in bovine serum albumin is sufficient to initiate the reaction immediately after mixing, which reaches equilibrium in about 15 min. On the other hand, half this amount is not sufficient to initiate the reaction, so that the reaction is delayed by about 150 s. Such a single-shot time-resolved experiment showed that experiments with a time interval of 100 ms are possible with repeated multi-shot runs.

Universality of the coexistence curves in a polymer solution

On the basis of a geometrical consideration on the surface and of the homogeneous properties for coexistence curves, we deduce a scaling form τ/τc =F(φ/φc) for the family of coexistence curves in a polymer solution, where τ is the reduced temperature, τc the critical reduced temperature, φ the concentration, and φc the critical concentration. It is shown that the scaling form provides a reasonable representation of existing experimental results. The relevance to some current theoretical predictions of this equation is discussed.

Temperature dependence of the structure of aggregates of tobacco mosaic virus protein at pH 7.2. Static synchrotron small-angle X-ray scattering.

The small-angle X-ray scattering (SAXS) method using a synchrotron radiation source was applied to the study of the self-aggregation process of tobacco mosaic virus protein (TMVP) at a concentration of 5.0 or 12.0 mg ml-1 in 50 mM or 100 mM-phosphate buffer (ionic strengths approx. 0.1 and 0.2, respectively) at pH 7.2 in the temperature region of 4.8 to 25.0 degrees C. This paper presents the results of static measurements of SAXS. Sedimentation velocity experiments were performed simultaneously under the same conditions. These results are qualitatively parallel to those of the SAXS measurements, although the size of stacked disks derived from the SAXS measurements is larger than that derived from the sedimentation experiments, suggesting a change in the equilibrium conditions in the centrifugal field. Qualitative analysis of the SAXS data with model simulation calculations implies that the aggregation of TMVP consists of two steps: (1) the aggregation of A-protein comprising a few subunits to form double-layered disks; and (2) the random polymerization of double-layered disks by disk-stacking. Increase in temperature, ionic strength or protein concentration induced TMVP to polymerize to form a double-layered disk or a quadruple-layered short rod with consumption of A-proteins, accompanied by a small number of multi-layered short rods. The SAXS results indicate that the A-protein and the multilayered short rods are polydisperse with respect to size and shape, i.e. the mixture of A-protein, double-layered disks and multi-layered short rods coexists in the equilibrium state without pressure-induced partial dissociation of TMPV as observed during normal ultracentrifugation, and even under solution conditions in which the formation of double-layered disks or higher-order aggregates is favored.

The morphology of bone mineral as revealed by small-angle X-ray scattering

Diffuse small-angle X-ray scattering of oriented bone from bovine femur and canine femur was described in terms of an ideal isotropic two-dimensional two-phase system which consists of mineral phase and organic phase. The microstructure of powdered, randomly-oriented bone from bovine femur was found to be affected by grinding. An analysis of small-angle scattering from oriented bone showed that bone mineral was to a large extent in the form of needle-like particles with a 50-60 A the diameter, and the dimension of organic phase transverse to the longitudinal axis of long bone was in the range 45-55 A. The intersect distribution function was directly calculated from the scattering intensities, and the results strongly suggested the presence of needle-like mineral with sharp edges.

Shear viscosity measurements near a multicomponent fluid tricritical point

Shear viscosity measurements have been performed near the tricritical point of an ethanol– water–benzene–ammonium sulfate mixture. A weak divergence was obtained in the range of 7×10−4<(T−Tt*) /Tt*<10−2, where Tt* is a tricritical spinodal temperature. The results are compared with the existing theories.

Ultrasonic shear spectrum in hydrated diethylamine melanins and its relation to stacking in a planar group

Shear mechanical relaxation and resonance data are reported for 20 wtu2009% hydration of diethylamine melanins with different pH values ranging from 2 to 7. Shear impedance measurements in the temperature range from 60 to −80u2009°C, with frequencies from 1 to 362 MHz, indicate a Davidson–Cole spectrum in the primary relaxation and a single relaxation with a characteristic frequency of f = 4 MHz at 60u2009°C referred to the molecular motions of a group composed of an average molecular weight Mn?1.4×104. A resonance at 250 MHz is found in the specific melanin called No. 1, associated with stacking of indole monomer units, and a single relaxation at f = 270 MHz at 60u2009°C is found in the hydrate of melanin No. 2. The nature of the stacking is surveyed on account of Fitzgerald’s theory. The limiting shear modulus in the primary relaxation related to the molecular motion of backbone chains obeys the modified Hirai–Eyring equation. All the hydrations have an amorphous phase composed of a three‐dimensional network structure.

Critical dynamic viscosities in a binary mixture

Ultrasonic shear measurements were conducted on polystyrene-cyclohexane solutions at 3, 51, and 252 kHz using the crystal fork and torsion methods. The real and imaginary parts of the complex shear modulus above the critical point are compared with modified theoretical expressions derived within the framework of the decoupled-mode theory. For this comparison, a background part was assumed to be described by a scaling form proposed by de Gennes. Numerical analysis of the data shows a satisfactory agreement between the theory and the experiments for ultrasonic shear data over a wide range of reduced frequencyω ... In addition, it is shown that the description of the simple viscosity dynamical scaling function is broken at a high-frequency limit.