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At least 19 recordsLinked to original sources
PubMed1985

A study of dynamic development in radiolesion and cell death of eukaryotes after exposure to ionizing radiation--the visualization of the dynamic reaction by means of cytochemical method with lactate dehydrogenase (LDH) as a nuclear marker and radiation-induced nuclear anomalization by an ultramicrostructural manifestation: a dynamic explanation.

The present work deals with the radiation effect on adult rats suffering from acute, whole-body irradiation with cobalt-60 gamma rays of dosages 100R and 300R respectively. The morphological alteration of the lymphocytic nucleus and exhibition of cytochemical reaction of LDH in intra- or extra-nuclear region has been observed at the end of predetermined time intervals after irradiation. A close relationship between the percentage of damage of the lymphocytic nucleus and that of positivity of LDH reaction is seen from their variations with time parallel. From technical color microphotographs which exhibit cytochemical reactions, the existence of enzyme LDH in the nucleus so far obscure has been visually recognized. The events happening in enzymic reaction and the leakage of enzyme across the nuclear envelope reflect the dynamic nature. The ultrastructural alteration of nuclear anomalization confirms the dynamic development of inducing radiolesion. The experimental facts inspire us to attempt an explanation of cellular radiolesion and cell death owing to ionization radiation in light of the dynamic concept.

Animals↗
PubMed1979

Dynamic cooperativity of molecular processes in active streaming, muscle contraction, and subcellular dynamics: the molecular mechanism of self-organization at the subcellular level.

Life phenomena are a kind of ordered dynamics appearing in macroscopic systems, living systems. Schrödinger has proposed a molecular mechanism for the organization of life phenomena, i.e., 'order-from-order' mechanism where ordered dynamics are composed of molecular dynamics having order as the ordered dynamics of a watch is caused by orderly movements of its mechanical elements. However, neither evidence supporting the 'order-from-order' mechanism has been found in living systems nor the reason why molecular dynamics acquire order instead of disorder has been elucidated for more than 30 years. The latter is quite anomalous from the point of views of thermodynamics, which is based on disordered behaviors of molecules. In this paper, we verify from studies of a streaming system reconstituted from rabbit skeletal F-actin and HMM that one life phenomenon, active streaming, is caused by the 'order-from-order' mechanism. This is also the case for muscle contraction. Moreover, it is probable that this mechanism generally works at the subcellular level, not only in biological motilities but also in life phenomena at biomembranes. We also clarify that dynamic cooperativity among molecule gives rise to order in molecular dynamics. Hence, dynamic cooperativity is the key mechanism for life phenomena caused by the 'order-from-order' principle at the subcellular level. To produce dynamic cooperativity it is necessary for component molecules or elements to have three states, i.e., inactive (stable) state 0, energized or energy storing (quasi-stable) state 1, and active (unstable) state 2. Each molecule performs elementary cycle 0 yields 1 yields 2 yields 0 repeatedly by using free energy at the molecular level. In a state far from thermodynamic equilibrium dynamic cooperativity is yielded in 2 yields 0 due to a kind of triggering action of neighboring elements and breaks thermodynamic detailed balance. In addition, dynamic cooperativity gives component molecules long-range interactions which depend on the structure of organelles or molecular assemblies. Dynamic cooperativity is able to decrease entropy production and will give a high efficiency in chemo-mechanical conversions. Great progress would be achieved in the understanding of the molecular mechanisms and thermodynamic principles of energy transformations in biological systems, if molecular dynamics during transformation could be directly observed. This is not only because physical changes accompanied by specific movements of macromolecules are essentially involved but also because such molecular movements play a substantial role in energy transformation. Entirely new ideas will be needed for this purpose although high voltage electron microscopy or X-ray diffraction, for instance, is now expected as to be one of the possible tools in the future. Fortunately even at present it is possible to obtain important information on molecular dynamics from biochemical and physiological data, if analyses are properly performed...

Actomyosin↗
PubMed1985

A comparison of the effects of mixed static and dynamic work with mainly dynamic work in hot conditions.

Current physiological criteria for limiting work in hot conditions are frequently based on responses to mainly dynamic work (eg treadmill walking). Their applicability to industrial situations containing mixed static and dynamic work is questioned, since the physiological responses to static work are different from those of dynamic work. Each of eight subjects attempted a one hour uphill treadmill walk (mainly dynamic work), and an uphill treadmill walk whilst intermittently carrying a 20 kg weight in the arms (mixed static and dynamic work). The external work rates in the two conditions were equal, effected by lowering the treadmill gradient in the loaded condition. Experiments were conducted in a hot climate (33 degrees C dry bulb, 25 degrees C wet bulb). Oxygen consumption, minute ventilation, sweat rate and rated perceived exertion were all significantly higher (p less than 0.001) for the mixed static and dynamic work than for the dynamic work. This was also the case for heart rate and forearm skin temperature (p less than 0.01), and for auditory canal temperature (p less than 0.05). There was no significant difference between the two types of work for mean skin temperature, calf skin temperature and chest skin temperature. These results show that for the same external work, physiological strain and perceived exertion are greater for mixed static and dynamic work (carrying a load in the arms) than for mainly dynamic work (walking on a treadmill). They suggest that it is not appropriate to make direct comparisons of laboratory studies based on dynamic work, with practical situations containing mixed static and dynamic work in the heat.

Adult↗
PubMed1990

Slowly adapting type I mechanoreceptor discharge as a function of dynamic force versus dynamic displacement of glabrous skin of raccoon and squirrel monkey hand.

The effects of dynamic force and dynamic displacement on single unit discharge rate during ramp stimulation were examined in 10 raccoon and 8 squirrel monkey slowly adapting Type I (SAI) mechanoreceptive afferent fibers, all having receptive fields on glabrous skin of the hand. In all 18 cases, power function exponents were higher for effects of dynamic displacement than for effects of dynamic force on discharge frequency. Thus, these SAI mechanoreceptors are more sensitive to variations in dynamic displacement than to variations in dynamic force. This differential sensitivity may be explained by the fact that the relationship between dynamic force and dynamic displacement is, itself, nonlinear, dynamic displacement being a power function of dynamic force, with exponents less than 1.0.

Action Potentials↗
PubMed1991

Dynamic light scattering from weakly bending rods: estimation of the dynamic bending rigidity of the M13 virus.

A theory is presented for the dynamic structure factor [S(K,t]) of weakly bending rods. This treatment is based on a discrete bead model for the Brownian dynamics in which all bead motions associated with bending are constrained to occur in a plane perpendicular to the end-to-end vector, thus prohibiting extension or contraction along that axis. Preset hydrodynamic interactions are incorporated in a numerically exact manner. The predicted normalized dynamic structure factor S(K,t)/S(K,0) should be valid for short times t such that the rms rotation of the end-to-end vector around any transverse axis is much less than 1.0 radian. With geometrical parameters appropriate for the M13 virus, the intensity autocorrelation function G(2) (K,t) = 1 + magnitude of S(K,t)/S(K,0)2 is calculated over a range of times and scattering vectors K for selected values of the persistence length P. The calculated G(2) (K,t) are fitted to a single exponential with unit baseline over the same range of times as the experimental photon correlation functions, and the apparent diffusion coefficients Dapp (K) are obtained from the best-fit relaxation times. For the sake of completeness, an exact expression is derived for the apparent diffusion coefficient obtained from the initial slope of the dynamic structure factor. However, this does not reduce to the known correct result in the rigid rod limit. To obtain the correct result, the limit of infinite bending rigidity must be taken before the limit of zero time. For this and other reasons, the initial slope value of Dapp (K) is not useful for weakly bending rods. Photon correlation functions are measured for the M13 virus, which is virtually identical to the often-studied fd virus. The experimental photon correlation functions are fitted over 8 relaxation times to a single-exponential plus baseline, and the Dapp (K) are calculated from the best-fit relaxation times. Theoretical curves of Dapp (K) vs K2 for selected values of P are compared with the experimental data, which are satisfactorily reproduced when P = 22000 +/- 2000 A. This dynamic value is close to the static value, P = 20000 +/- 2000 A, reported for the very similar fd virus. The most recent theories of Maeda and Fujime and their dynamic light scattering studies of fd virus are compared with the present results in some detail. Their optimum value of P is in surprisingly good agreement with the present value.

Bacteriophages↗
PubMed1992

Long-term changes after brief dynamic psychotherapy: symptomatic versus dynamic assessments.

Dynamic change in psychotherapy, as measured by theory-related or mode-specific instruments, have been criticized for being too intercorrelated with symptomatic change measures. In this study, long-term changes after brief dynamic psychotherapy were studied in 45 moderately disturbed neurotic patients by a reliable outcome battery. The factor structure of all the change variables suggested that they tapped 2 distinct and stable sources of variance: dynamic and symptomatic change. The categories of overall dynamic change were different from categories of change on the Global Assessment Scale. A small systematic difference was found between the categories of overall dynamic change and the categories of target complaints change also, due to false solutions of dynamic conflicts.

Adult↗
PubMed1979

Comparison of cardiovascular responses to static-dynamic effort and dynamic effort alone in patients with chronic ischemic heart disease.

Thirty men, mean age 55 years, known to have treadmill-induced ischemic ST-segment depression, performed static and dynamic effort, i.e., forearm lifting and treadmill exercise, separately and combined. Static effort was sustained at 20%, 25% or 30% of maximal forearm lifting capacity. Two symptom-limited treadmill tests, one with and one without added static effort, were performed on each of two visits. Compared with dynamic effort alone, combined static-dynamic effort decreased treadmill work load and increased heart rate, systolic blood pressure and rate-pressure product at the onset of ischemic ST-segment depression or angina pectoris: 7.1 +/- 0.4 vs 8.0 +/- 0.5 (SEM) multiples of resting oxygen consumption (mets), estimated; 141 +/- 3 vs 134 +/- 3 beats/min; 170 +/- 4 vs. 162 +/- 4 mm Hg and 239 +/- 8 vs 218 +/- 9 (p less than 0.001). The prevalence of angina pectoris was significantly less with combined static-dynamic effort than with dynamic effort alone. Static effort causes a resetting of the threshold at which ischemic abnormalities appear during dynamic effort.

Angina Pectoris↗
PubMed1989

A simple formulation of microtubule dynamics: quantitative implications of the dynamic instability of microtubule populations in vivo and in vitro.

A simple formulation of microtubule dynamic instability is presented, which is based on the experimental observations by T. Horio and H. Hotani of coexisting, interconverting growing and shrinking microtubules. Employing only three independent, experimentally determined parameters for a given microtubule end, this treatment accounts quantitatively for the principal features of the observed dynamic behaviour of steady-state tubulin microtubules in vitro. Experimental data are readily reproduced for microtubule length redistribution, and for the kinetics of tubulin exchange processes, including pulse-chase properties. The relative importance of dynamic incorporation and that due to treadmilling are assessed. Dynamic incorporation is found to dominate the overall exchange properties; polarized incorporation due to treadmilling generally becomes significant only when the dynamics are largely suppressed. This treatment also permits simulation of certain cellular phenomena, showing how microtubule renucleation can control microtubule growth, by means of changes in microtubule number concentration in a system at constant microtubule mass. A relatively simple extension of the formulation accounts quantitatively for non-steady-state microtubule properties, e.g. dilution-induced rapid disassembly and the oscillatory mode of microtubule assembly. The principles relating dynamic instability and oscillatory behaviour are clearly indicated. Possible mechanisms of the switching of microtubules are briefly discussed.

Animals↗
PubMed1990

[Analysis of the denture dynamics in R.P.D.'s. 2. Influence of retainers on the dynamics of free-end-saddle].

The ordinary denture movement during function is defined as the "Denture dynamics" in R.P.D.'s. by K. H. Körber (1975). The Author has already reported the evaluating method of the denture dynamics objectively by two ways: The displacement sensors of magnetoresistors detected the vertical and horizontal movements of denture saddle in free end situation. Tiny accerelometer also detected the accerelation during the movements. In this present study, the correlations among the retainers used, the extent of the denture dynamics in displacement and accerelation, the occluding force and the abutment tooth mobility induced by the denture support were correlatively evaluated in two patients with class I free end R.P.D.'s. with interchangeable retainers by above methods. All the data were collected simultaneously by the electronic measuring and recording apparatus. Following results were obtained: 1. The denture dynamics depended on the selection of retainers examined. The extent of the dynamics reduced from the denture with the wrought wire clasps, the denture with the cast clasps, then to the denture with cone crown telescopes in sequence. 2. The occluding force increased just as the changes in sequence of the denture dynamics. 3. The abutment tooth moved to the distal in each case. The highest value of the mobility was found in the denture with the cast clasps, then in the denture with the wrought wire clasps. The least value of the tooth mobility was found in the denture with the cone crown telescopes. These results will strongly support the concept of the free end saddle R.P.D.'s anchored and supported rigidly by the abutments and the residual ridges in clinics.

Dental Abutments↗
PubMed1988

Dynamics of microtubules visualized by darkfield microscopy: treadmilling and dynamic instability.

Individual microtubules undergoing treadmilling in vitro were visualized by darkfield light microscopy, and the relationship between treadmilling and dynamic instability was studied as a function of microtubule-associated proteins (MAPs). In order to demonstrate treadmilling directly by real-time observation, we constructed three-block microtubules, the center-block of which was decorated with Tetrahymena dynein. The decorated block can easily be distinguished from undecorated blocks in the darkfield microscope because the decorated one appears much thicker. At steady-state conditions, the length of an undecorated block at one end increased and that at another end decreased, while the decorated center-block did not change in its length. The results from these direct observations show that calf brain 3X-microtubules exhibit a treadmilling flux of 0.9 micron/h. Using a similar microscopy technique, we previously demonstrated that phosphocellulose PC-microtubules existed in either the growing or the shortening phase and alternated quite frequently at steady-state conditions (dynamic instability). How does treadmilling relate to dynamic instability? An image recording of individual 3X-microtubules containing MAPs revealed that the microtubules undergo treadmilling and do not exhibit any dynamic instability. This evidence shows that MAPs suppress the dynamic instability of microtubules. That is, treadmilling can take place in the steady state only after microtubules have been stabilized by MAPs.

Animals↗
PubMed1990

Conformational and helicoidal analysis of the molecular dynamics of proteins: "curves," dials and windows for a 50 psec dynamic trajectory of BPTI.

A new procedure for the graphic analysis of molecular dynamics (MD) simulations on proteins is introduced, in which comprehensive visualization of results and pattern recognition is greatly facilitated. The method involves determining the conformational and helicoidal parameters for each structure entering the analysis via the method "Curves," developed for proteins by Sklenar, Etchebest, and Lavery (Proteins: Structure, Function Genet. 6:46-60, 1989) followed by a novel computer graphic display of the results. The graphic display is organized systematically using conformation wheels ("dials") for each torsional parameter and "windows" on the range values assumed by the linear and angular helicoidal parameters, and is present in a form isomorphous with the primary structure per se. The complete time evolution of dynamic structure can then be depicted in a set of four composite figures. Dynamic aspects of secondary and tertiary structure are also provided. The procedure is illustrated with an analysis of a 50 psec in vacuo simulation on the 58 residue protein, bovine pancreatic trypsin inhibitor (BPTI), in the vicinity of the local minimum on the energy surface corresponding to a high resolution crystal structure. The time evolution of 272 conformational and 788 helicoidal parameters for BPTI is analyzed. A number of interesting features can be discerned in the analysis, including the dynamic range of conformational and helicoidal motions, the dynamic extent of 2 degrees structure motifs, and the calculated fluctuations in the helix axis. This approach is expected to be useful for a critical analysis of the effects of various assumptions about force field parameters, truncation of potentials, solvation, and electrostatic effects, and can thus contribute to the development of more reliable simulation protocols for proteins. Extensions of the analysis to present differential changes in conformational and helicoidal parameters is expected to be valuable in MD studies of protein complexes with substrates, inhibitors, and effectors and in determining the nature of structural changes in protein-protein interactions.

Biological Evolution↗
PubMed1986

Molecular dynamics simulations of the holo and apo forms of retinol binding protein. Structural and dynamical changes induced by retinol removal.

The effects of removing retinol from the X-ray structure of holo-retinol binding protein are studied using the molecular dynamics technique. Structural and dynamical properties emerging from an 80 ps simulation of the apo form, for which no crystallographic structure is available, are compared with the results of a 70 ps trajectory of the holo-protein. Dynamical stationarity is attained after roughly 30 ps, and the resulting average structure is proposed as a reasonable model of the apo-protein. Conformational changes are observed for the loops at the beta-barrel entrance during the non-equilibrium part of the apo-trajectory. Tryptophan labelling experiments and retinoid reconstitution experiments point towards this part of the molecule as being involved in prealbumin binding. Structural changes in this region may therefore explain the differences in prealbumin affinity between the apo and holo forms. Furthermore, a change in the position of the alpha-helix, corresponding to a pivot around its C terminus, is observed for the apo-protein. The resulting conformation of the alpha-helix is found to be similar to that in apo-beta-lactoglobulin, which also can bind retinol and for which a crystal structure exists. The results from the holo simulation are compared to the crystallographic data and show good agreement. The dynamics of the secondary and tertiary structural elements are analysed and compared for the two forms. The beta-barrel is found to be extremely cooperative in its atomic motions in both simulations, and the top and bottom beta-sheets perform collective fluctuations with respect to each other in the low-frequency limit of the simulations. The dynamics of the alpha-helical region presents clear differences between the two forms; while the holo-protein has a well-defined spectrum for the longitudinal stretching mode, the apo form displays a fairly large bending of the alpha-helix at several points of the trajectory.

Computer Simulation↗
PubMed1992

["Dynamic" MR imaging of the cervical cord in patients with cervical spondylosis and ossification of the posterior longitudinal ligament--significance of dynamic cord compression].

This investigation was designed to assess the influence of dynamic cord compression on severity and course of myelopathy. Sixty-seven patients studied comprised 54 cases of cervical spondylosis and 13 cases of ossification of the posterior longitudinal ligament. These patients underwent "dynamic" MR imaging of the cervical spine. MR images in the sagittal view were obtained in three different neck positions: flexion, neutral, and extension. MR imaging was performed with a 0.15 T resistive unit. For technical reasons, the body coil was used. The pulse sequence was 500/30 (Tr msec/echo time msec) for T1 images. The spinal cord compression was accelerated in 32 cases when extended, in 2 cases when flexed, and in 4 cases when both extended and flexed. In 21 cases, we compared myelograms with MR images in a same neck position. Findings of myelograms well corresponded with those of MR images on 83 percent of intervertebral levels. The patients with dynamic cord compression were proved to have severer long tract signs, and their disability was regressive or progressive case by case for an average of 21-month follow-up. The "dynamic" MR imaging can provide dynamic nature of spinal cord compression, and prognostic clues.

Cervical Vertebrae↗
PubMed1992

Molecular dynamics studies of a DNA-binding protein: 2. An evaluation of implicit and explicit solvent models for the molecular dynamics simulation of the Escherichia coli trp repressor.

Although aqueous simulations with periodic boundary conditions more accurately describe protein dynamics than in vacuo simulations, these are computationally intensive for most proteins. Trp repressor dynamic simulations with a small water shell surrounding the starting model yield protein trajectories that are markedly improved over gas phase, yet computationally efficient. Explicit water in molecular dynamics simulations maintains surface exposure of protein hydrophilic atoms and burial of hydrophobic atoms by opposing the otherwise asymmetric protein-protein forces. This properly orients protein surface side chains, reduces protein fluctuations, and lowers the overall root mean square deviation from the crystal structure. For simulations with crystallographic waters only, a linear or sigmoidal distance-dependent dielectric yields a much better trajectory than does a constant dielectric model. As more water is added to the starting model, the differences between using distance-dependent and constant dielectric models becomes smaller, although the linear distance-dependent dielectric yields an average structure closer to the crystal structure than does a constant dielectric model. Multiplicative constants greater than one, for the linear distance-dependent dielectric simulations, produced trajectories that are progressively worse in describing trp repressor dynamics. Simulations of bovine pancreatic trypsin were used to ensure that the trp repressor results were not protein dependent and to explore the effect of the nonbonded cutoff on the distance-dependent and constant dielectric simulation models. The nonbonded cutoff markedly affected the constant but not distance-dependent dielectric bovine pancreatic trypsin inhibitor simulations. As with trp repressor, the distance-dependent dielectric model with a shell of water surrounding the protein produced a trajectory in better agreement with the crystal structure than a constant dielectric model, and the physical properties of the trajectory average structure, both with and without a nonbonded cutoff, were comparable.

Amino Acid Sequence↗