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Biomedical subjects

S Fujime

Publications and source records attributed to S Fujime.

At least 19 recordsLinked to original sources
PubMed1990

Elastic behavior of zymogen granule membranes in response to changes in pH and pCa.

In the process of secretion, the membrane of secretory granules is expected to change its elastic behavior. Elastic modulus of the membrane of zymogen granules, prepared from the rat pancreas acinar cell, was measured by an osmotic swelling method. The elastic modulus of the granule membrane at pCa 8 reduced from the maximal value of 230 dyn/cm at pH 6.0 to almost zero at pH 7.5. In a cytosol of an acinar cell, calcium ions play an important role as a second messenger in secretion. The elastic modulus of the granule membrane reduced in a sigmoidal fashion at pCa between 7.0 and 6.0. This range of pCa corresponds to a physiological rise of free Ca2+ concentrations in the cell cytosol when stimulated by external secretagogues. Reduction of the elastic modulus indicates that the state of the granule membrane switches to a more flexible one in which the granule is easy to appose to the cell plasma membrane and then swell as a final step of exocytosis.

Animals↗
PubMed1988

Regulation by Ca2+ of membrane elasticity of bovine chromaffin granules.

In a range of [Ca2+] similar to cytosolic transient, a drastic reduction from about 20 dyn/cm to almost zero was observed in the membrane elastic modulus of bovine chromaffin granules, isolated in a solution containing 0.3 M sucrose and 5 mM Hepes at pH 7.0, and measured by combination of osmotic swelling and dynamic light-scattering (DLS) methods. This result suggests that the granule membrane becomes extremely flexible as a prelude to exocytosis.

Animals↗
PubMed1988

Dynamic light scattering from polydisperse suspensions of large spheres. Characterization of isolated secretory granules.

Dynamic light scattering is useful in determining the diameter of submicrometer particles in suspension. When both static scattering intensity P(K) and apparent diffusion coefficient D can be measured in a wide range of the length of the scattering vector K, it is possible to determine the number-average diameter dn and sharpness in size distribution of spheres. We derived approximate, but very simple, expressions for mean value of P(K) and mean value of D/D(dn) applicable to very large spheres for which the so-called Rayleigh-Debye condition is perturbed, where mean value of ... stands for the size average. These approximate expressions were compared with the numerical results based on the Mie scattering theory. Experimental results for isolated secretory granules, zymogen (dn approximately 800 nm) and chromaffin (dn approximately 400 nm) granules, were analyzed by use of the present formulation, and the dispersion in size distribution, sigma/dn = [(the mean of d2)/d2n - 1]1/2, was found to be about 0.2 for both types of granules.

Animals↗
PubMed1988

Dynamic light scattering from polydisperse suspensions of thin ellipsoidal shells of revolution with submicron diameters.

Osmotic swelling of membrane vesicles has been studied in combination with dynamic light scattering, to obtain information about the elastic properties of biomembranes. In such studies, there arise some technical problems specific to dynamic light scattering, which include the effects on the light-scattering results of the size distribution and nonsphericity of the vesicles with submicron sizes. Even for highly monodisperse suspensions of spherical vesicles (sigma/dn = [(the mean of d2)/d2n-1]1/2 = 0.1; dn being the number-average diameter of vesicles), the average diameter d obtained from dynamic light scattering is shown to be strongly dependent on dnK, where K is the length of the scattering vector. This is solely due to the shell structure of the vesicles. For ellipsoidal vesicles, another complication appears which is due to the rotational motion of ellipsoids.

Animals↗
PubMed1988

Change in membrane elastic modulus on activation of glucose transport system of brush border membrane vesicles studied by osmotic swelling and dynamic light scattering.

The cell membrane having a transport system is inferred to be flexible when its function is being activated. For the brush border membrane vesicles prepared from rat small intestine, which have the co-transport system of Na+ and glucose, the membrane elasticity was measured as a function of the d-glucose concentration in the presence of Na+ ions. The elastic modulus of the vesicle membrane was obtained by an osmotic swelling method. Osmolality was changed by diluting the extravesicular d-mannitol concentration. The change in the diameter of the membrane vesicle in response to an osmolality change was measured by the dynamic light-scattering method. The elastic modulus of the vesicle membrane decreased from 150 dyn/cm to 80 (45) dyn/cm with the increase of d-glucose, from 0 mM to 10(30) mM in the presence of 10 mM Na+ ions. On the other hand, in the presence of 1 mM phlorizin, a glucose-transport inhibitor, the elastic modulus remained at a constant value of 160 dyn/cm in the same range of the d-glucose concentration. This indicates that the vesicle membrane becomes flexible when its transport function is activated. In a broad osmolality range, the brush border membrane vesicle showed cycles of "swell-burst-reseal". The vesicle membrane became flexible after every cycle, namely, the modulus was 150, 120, and 55 in units of dyn/cm in the presence of 1 mM d-glucose and 50 mM Na+ ions.

Alkaline Phosphatase↗
PubMed1987

Dynamic light-scattering study of muscle F-actin. II.

By dynamic light scattering, the intensity autocorrelation function, G2(tau) = B[1 + beta[g1(tau)[2], was obtained over the scattering angles (theta) from 30 to 130 degrees in steps of 10 degrees for semidilute solutions of muscle F-actin and of F-actin complexed with heavy meromyosin in the absence of ATP (acto-HMM), where B is the baseline and beta a constant. The main findings were: (1) A 0.5 mg/ml F-actin solution gave nonreproducible spectra at theta less than or equal to 40 degrees but quite reproducible spectra at theta greater than or equal to 50 degrees, with beta = 0.9-0.8 at all theta values. Nonreproducibility of spectra at low theta values was concluded to be due to restricted motions of very long filaments confined in cages or zig-zag tubing formed by a major fraction of filaments, where the very long filaments were those at a distant tail of an exponential length distribution and the major fraction of filaments were those with lengths around Ln-2Ln, Ln being the number-average length. Spectral widths were compared with theoretical ones for rigid rods averaged over the length distribution with Ln = 900 nm, and were suggested to be largely contributed at high theta values from bending motions of filaments. (2) Acto-HMM solutions at 0.5 mg/ml F-actin and at weight ratios of HMM to F-actin of 0.5-2 gave spectra which, with respect to theta, behaved very similarly to those of F-actin alone. The spectral widths, however, drastically decreased with the weight ratio up to unity and stayed virtually constant above unity. In contrast to a previous study (F.D. Carlson and A.B. Fraser, J. Mol. Biol. 89 (1974) 273), beta values of acto-HMM were as large as those of F-actin alone. Acto-HMM was concluded to travel a distance far greater than 1/K with a mobility smaller than that of F-actin, where K = (4 pi/lambda) sin(theta/2), lambda being the wavelength of light in the medium. These results suggest that acto-HMM gels are very soft even though they did not pour from an inverted cell. Based on several intuitive models which give a mutual relationship between the beta value and modes of motion of scatterers, we discuss the restricted motions responsible for nonreproducibility of spectra at low angles and large beta values of acto-HMM gels at all theta values and weight ratios so far studied.

Actins↗
PubMed1987

Dynamic light-scattering study on changes in flexibility of filamentous bacteriophage Pf1 with temperature.

The temperature dependence of the flexibility of bacteriophage Pf1 was investigated by dynamic light scattering, and the following results were obtained: The gamma/K2 values measured at 1 degree-25 degrees C and at various K values were T/eta-scaled to 20 degrees C, where gamma is the first cumulant of the field correlation function of scattered light, K is the length of the scattering vector, T is the absolute temperature, and eta is the solvent viscosity at T. And it was found that the scaled gamma/K2 values at low K values were independent of temperature, whereas those at high K values increased sigmoidally and reversibly against temperature. This suggests that the virion is more flexible at temperatures above the transition temperature Tt. This characteristic temperature Tt depended on the pH of the suspension: Tt = 11 degrees C at pH 6.9 and Tt = 8 degrees C at pH 8.2.

Bacteriophages↗
PubMed1986

Dynamic light-scattering study on polymerization process of muscle actin.

Globular actin (G-actin) polymerizes into a fibrous form (F-actin) under physiological salt conditions. The polymerization process of muscle actin was studied by a dynamic light-scattering method. The intensity correlation functions G2(tau) of scattered light from a G-actin solution containing 2 mM Tris-HCl (pH 8.0) and 0.1 mM ATP were analyzed by a cumulant expansion method, and the translational diffusion coefficient was determined to be D = (8.07 +/- 0.10) X 10(-7) cm2/s at 20 degrees C. This D value gave a diameter of 5.3 nm for spherical G-actin including a hydration layer. Polymerization of 1-3 mg/ml G-actin in a solution containing 10 mM Tris-HCl (pH 8.0), 0.2 mM ATP and 60 mM KCl was followed by successive measurements of G2(tau) for a data accumulation period of 60-300 s/run. The time evolution of G2(tau) was analyzed by a least-squares fitting to the field correlation function of a multiexponential form g1(tau) = sigma iAi exp(-gamma i tau) with gamma 1 greater than gamma 2 greater than 3 greater than ..., and the static scattering intensity I(t) = mean value of I as a function of time t after initiation of polymerization was decomposed as I(t) = mean value of I sigma iAi. At the early stage of polymerization, a two-exponential fit gave results indicating that component 1 came from G-actin and component 2 from F-actin growing linearly with t. At the middle stage of polymerization, a three-exponential fit gave the results that component 1 came from G-actin and possibly its small oligomers, component 2 from polymers with a number-average length Ln of about 900 nm which was independent of t, and component 3 from 'ghosts' in dynamic light scattering in a semidilute regime. Component 3 was concluded to arise from restricted motions of polymers with lengths much longer than Ln in cages formed by polymers giving component 2, and a fragmentation-elongation process of F-actin was suggested to start at the middle stage of polymerization, resulting in the size redistribution of F-actin.

Actins↗
PubMed1979

Physicochemical properties of pyocin F1.

The physiochemical properties of pyocin F1 were studied. Pyocin F1 consists of flexuous rod-like particles homogenous in size. Each particle was composed of rod and fiber parts. The rod part was 105.5 +/- 9.5 nm long and 10.0 +/- 1.4 nm wide, and showed regular striations amounting to 23 layers. The fiber part was composed of several filaments; the length of the longest filament was 43.0 +/- 12.0 nm. The amino acid composition, the partial specific volume (0.720 ml/g), the sedimentation coefficient (S020,W = 35.1S), and the translational diffusion constant (0.94 +/- 0.01 x 10(-7) cm2/s) were determined. The particle weight was calculated to be 3.23 x 10(6) daltons.

Amino Acids↗
PubMed1978

Optical diffraction study of muscle fibers. II. Electro-optical properties of muscle fibers.

When an electric field is applied along the fiber axis, the intensities of all observable optical diffraction lines of skeletal muscle fibers increase. This electro-optical effect was extensively studied and it was confirmed that the effect is due to the interaction between electric dipole moments of thin filaments and the applied field. From the present study on the intensity modulation due to applied field in sinusoidal and square forms, we confirmed that (1) the thin filament is a semiflexible rod, (2) the second order mode of the bending motion of thin filaments contributes to the electro-optical effect of muscle fibers at higher frequencies of a sinusodidal field or shorter durations of a square field, (3) the induced moment has no appreciable effect, and (4) the estimated value of the flexural rigidity of thin filaments strongly depends on the concentrations of free calcium ions in the myofibrillar space.

Animals↗
PubMed1977

Dynamic characteristics of F-actin and thin filaments in vivo and in vitro.

Measurements of birefringence, ultraviolet dichorism and quasielastic light scattering were carried out on F-actin in solution and on the thin filaments of glycerinated myofibrils. The birefringence of the I-bands of myofibrils was of the same order of magnitude as that of F-actin or the F-actin-tropomyosin-troponin complex oriented in vitro at the same concentration. The ultraviolet dichroism spectrum of the I-bands was very similar to that of F-actin or the F-actin complex in vitro, which is due to orientation of bound ADP and tryptophan residues in F-actin. Quasielastic light scattering measurements, electronmicroscopic observations and the analyses of the electro-optic effect of the I-bands suggested approximately the same flexibility for F-actin in vitro and for the thin filaments in vivo. These optical measurements which were made under various conditions provide evidence for a conformational change induced by calcium ions in F-actin both in vivo and in vitro. This conformational change was found to be amplified by the interaction of F-actin with myosin. This is a brief review of our investigation on the dynamics of F-actin and the thin filament in vivo and in vitro by optical methods.

Actins↗
PubMed1975

Optical diffraction study of muscle fibers.

Skeletal muscle fibers act as a one-dimensional grating to electromagnetic waves in the optical frequency range. Results are presented of the optical diffraction study of frog sartorius muscle fibers. 1. A simple theoretical consideration predicts that, at a sarcomere length near 3 mum, the second-order reflection is contributed only by the thin filaments due to the destructive interference between scattered rays from thick filaments. At that sarcomere length, both the first-order and the third-order reflections are contributed by both kinds of filaments. 2. Intensity measurements of diffraction lines of muscle fibers at rest at various sarcomere lengths confirmed the validity of our theoretical prediction.3. The isometric contraction of skinned fibers was realized by the phoretic injection of Ca2+ from a micropipette. During the Ca2+ injection intensity drops of the diffraction lines were observed. At a very narrow range of sarcomere lengths near 3 mum, the intensity drop of the second-order diffraction line became very small on Ca2+ injection, whereas the intensity drops of both the first-order and the third-order diffraction lines were very large. 4. A theoretical analysis concludes that the intensity drops on Ca2'njection are solely due to small random fluctuations of the position of thick filaments in the sarcomeres.

Animals↗