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At least 685 records · Page 38Linked to original sources
PubMed1994

Reduced receptor aggregation and altered cytoskeleton in cultured myocytes after space-flight.

We carried out parallel experiments first on the slow clinostat and then in space-flight to examine the effects of altered gravity on the aggregation of the nicotinic acetylcholine receptors and the structure of the cytoskeleton in cultured Xenopus embryonic muscle cells. By examining the concordance between results from space flight and the clinostat, we tested whether the slow clinostat is a relevant simulation paradigm. Space-flown cells showed marked changes in the distribution and organization of actin filaments and had a reduced incidence of acetylcholine receptor aggregates at the site of contact with polystyrene beads. Similar effects were found after clinostat rotation. The sensitivity of synaptic receptor aggregation and cytoskeletal morphology suggests that in the microgravity of space cell behavior may be importantly altered.

Acetylcholine↗
PubMedDate not supplied

Metabolic changes in the animals subjected to space flight.

The activity of the enzymes involved in aminoacid metabolism (tyrosine aminotransferase, TAT, tryptophan pyrrolase TP, serine dehydratase, SD) with rapid response to glucocorticoids and enzymes requiring for activity increase repeated administration of corticosterone (alanine aminotransferase, ALT, aspartate aminotransferase, AST) in liver, the changes of lipolysis in adipose tissue and the plasma corticosterone levels were studied in rats subjected to space flight (F), in animals from synchron model experiments (SM, simulated conditions of space flight in laboratory) and in intact controls (C). The increase of plasma corticosterone concentration and of the activity of rapidly (TAT, TP, SD) and slowly activating enzymes (ALT, AST) was found in F group 6-10 hr after space flight (18.5 days on biosatellite COSMOS 1129). This suggested the presence of acute-stress (associated primarily with the landing) and chronic stress induced hypercorticosteronemia during the flight. After the short 6-day period of recovery the plasma corticosterone concentrations and the activities of liver enzymes returned to control levels. The exposition of animals to repeated immobilization stress showed higher response of corticosterone levels in flight rats as compared to intact controls. No changes in basal lipolysis were observed in flight rats in comparison to intact controls, however the stimulation of lipolysis by norepinephrine was lower in animals from F and SM groups. This lower response of lipolytic processes to norepinephrine was found in flight animals also after six days period of recovery. These results showed that there are important changes in the regulation of lipolytic processes in adipose tissue of rats after space flight and in the conditions of model experiments.

Adipose Tissue↗
PubMed2004

Demonstration of a low-energy on-pathway intermediate in a fast-folding protein by kinetics, protein engineering, and simulation.

It is controversial whether fast-folding proteins can form productive on-pathway intermediates that are more stable than the denatured state because noncovalent intermediates are usually evanescent. Here, we apply the classical criteria for the existence of intermediates: namely, the intermediates form and react rapidly enough to be on pathway and they can be isolated and characterized. The folding of the 71-residue, mainly alpha-helical FF domain from human HYPA/FBP11 fulfills these classical criteria, as was found for Im7. The FF domain folds in two phases, one on the micros and the other on the ms time scale. An engineered mutant folds only to a partly folded state, with some 20-40% of the native helical content. The kinetic properties of the mutant are identical to those found for the fast phase of the wild-type protein, and it is likely that the mutant folds just to the intermediate state. A full kinetic analysis of the folding of wild-type protein, using the amplitudes of its native and denatured states and the observed values for the mutant, rules out an off-pathway scheme but fits an on-pathway scheme, with a low energy intermediate that is modeled by the mutant. The experimental proof benchmarks a molecular dynamics method that identifies an obligatory intermediate observed in multiple simulations. The conformational space defining this intermediate is visited several times in the simulations, leading to high populations consistent with the presence of a low energy intermediate.

Kinetics↗
PubMed2005

Mesoscopic dynamic Monte Carlo simulations of the adsorption of proteinlike HP chains within laterally constricted spaces.

Two-dimensional dynamic Monte Carlo simulations are applied to the protein-like HP chain model to investigate the influence of lateral confinement of the adsorbed chain on adsorption thermodynamics and the ensemble of accessible chain conformations. The structure of the model makes it possible to enumerate all possible chain conformations and thereby define with precision the relation between adsorption thermodynamics and changes in accessible chain conformations resulting from the adsorption process. Lateral confinement of the adsorbed chain is shown to dramatically reduce the number of accessible energy states and unique chain conformations such that, under certain conditions, adsorption is predicted to actually stabilize the chain against denaturation. Lateral confinement preferentially eliminates expanded conformations of the adsorbed chain, shifting the equilibrium from the unfolded state toward the native state. As a result, the conformational entropy of the adsorbed chain is predicted to be lower than that of the chain free in solution. The protein-like HP chain responds to an increase in the hydrophobicity of the sorbent surface by strongly favoring those conformations that minimize the overall internal energy of the system. As a result, adsorption severely destabilizes the native-state conformation. The ability of our simulation results to provide insights into underlying mechanisms for nonspecific protein adsorption is illustrated through qualitative comparison with activity data for hen egg-white lysozyme adsorbed on silica at different surface concentrations.

Adsorption↗
PubMed2003

[Hormonal regulation of metabolism in the human body in microgravity and during simulation of its physiological effects].

The paper presents results of investigations into the effects of space flight and simulation experiments of various length on the hormonal regulation of metabolism in the human body. Microgravity was shown to instigate shifts on different levels of the hormonal regulation and consequent adjustment of metabolism to this new environment. For instance, adaptation occurs on the level of basal secretory activity resulting in altered metabolism and formation of a pool of hormones. Metabolism readaptation to the Earth's gravity is dependent on polymorphic processes in the system of hormonal regulation developing in the course of time. Trends in the hormonal regulation of water-electrolyte metabolism during early adaptation point to inequality of contributions of the antidiuretic hormone, natriuretic peptide, and the renin-angiotensin-aldosterone system. In the ground-based simulations responses of the hormonal regulation of water-electrolyte metabolism differ in intensity and types of hormones involved. Temperature variation can modify reactions of the comosis and volume regulating hormones at the beginning of adaptation. Physical-chemical regulation of calcium homeostasis in microgravity reveals itself by a rapid decline of the calcium-binding ability of blood buffers and, later on, degradation of the relative ability of extraplasmic structures to bind calcium. Qualitative and quantitative changes in the diurnal rhythm of the suprarenal steroidogenesis are indicative of modification of intensity of reactions of the main biosynthetic sequences. Countermeasures used by test-subjects in these investigations loosened significantly the aldosterone-secreting biosynthetic sequences but were favorable to the synthesis of testosterone and hydrocortisone. Some of the highly variable processes of hormonal regulation were mute to the diurnal rhythms in the pre-flight and preexperimental periods.

Adaptation, Physiological↗
PubMed1997

Secondary metabolism in simulated microgravity: beta-lactam production by Streptomyces clavuligerus.

Rotating bioreactors designed at NASA's Johnson Space Center were used to simulate a microgravity environment in which to study secondary metabolism. The system examined was beta-lactam antibiotic production by Streptomyces clavuligerus. Both growth and beta-lactam production occurred in simulated microgravity. Stimulatory effects of phosphate and L-lysine, previously detected in normal gravity, also occurred in simulated microgravity. The degree of beta-lactam antibiotic production was markedly inhibited by simulated microgravity.

Anti-Bacterial Agents↗
PubMed1978

Gas chromatographic head-space determination of residual acrylonitrile in acrylonitrile-butadiene-styrene resins and migration into a simulated fatty foodstuffs liquid.

Head-space methods are described for the determination of residual acrylonitrile in acrylonitrile-butadiene-styrene resins and in olive oil, which simulates fatty foodstuffs. Dimethylformamide was used as solvent for the resin, with flame ionization detection. The injection of water into the resin dispersion prior to head-space analysis greatly enhances the detection capabilities. The use of a nitrogen-selective detector required dimethyl sulphoxide as the solvent. The determination of acrylonitrile in olive oil was carried out employing both types of detector. The detection sensitivity was much greater with the nitrogen-selective detector.

Acrylonitrile↗
PubMed1989

Microgravity particle research on the space station: the Gas-Grain Simulation Facility.

In the gravitational field on Earth, the large settling rate of micron-sized particles and the effects of gravity-induced convection prohibit many interesting studies of phenomena such as coagulation, collisions, and mutual interactions of droplets, dust grains and other particles. Examples of exobiology experiments involving these phenomena are the simulation of organic aerosol formation in Titan's atmosphere, studies of the role of comets in prebiotic chemical evolution, and simulations of carbon grain interactions in various astrophysical environments. The Gas-Grain Simulation Facility (GGSF) is a proposed Earth-orbital laboratory that will allow present ground-based experimental programs which study processes involving small particles and weak interactions to be extended to a new domain. Physics issues that scientists wishing to propose GGSF experiments must consider are reviewed in this paper. Specifically, coagulation, motion in gases and vacua, and wall deposition of particles in a microgravity environment are discussed.

Acceleration↗
PubMed1990

Simulation of two-electron homogeneous electrocatalysis for steady-state voltammetry at hemispherical microelectrodes.

Expanded space grid digital simulation of second-order, two-electron homogeneous electrocatalysis was extended to slow scan voltammetry at hemispherical microelectrodes. Predictions of the simulations are examined for reversible and quasireversible heterogeneous charge transfer of catalyst for a range of homogeneous catalytic rate constants (k1) and electrode radii. Working curves of catalytic efficiency vs long k1 were generated assuming reacting species with equal diffusion coefficients. As electrode radii in the less than 10-microns range decrease, progressively larger homogeneous catalytic rates are needed to yield analytically significant amplification of limiting currents. Simulations using hemispherical radii of (2/pi)rd can be used to predict catalytic efficiencies for microdisk electrodes with radii rd. Simulated working curves were used to estimate a log k1 of 3.88 +/- 0.55 (M-1 s-1) for electron transfer from the anion radical of 9,10-diphenylanthracene to 4,4'-dibromobiphenyl from steady-state catalytic efficiencies obtained at carbon microdisk electrodes. This value was in good agreement with 3.90 +/- 0.16 M-1 s-1 found previously by cyclic voltammetry.

Catalysis↗
PubMed2001

Psychosocial issues in space: future challenges.

As the duration of space flights increases and crews become more heterogeneous, psychosocial factors are likely to play an increasingly important role in determining mission success. The operations of the International Space Station and planning of interplanetary missions represent important future challenges for how to select, train and monitor crews. So far, empirical evidence about psychological factors in space is based on simulations and personnel in analog environments (i.e. polar expeditions, submarines). It is apparent that attempts to transfer from these environments to space requires a thorough analysis of the human behavior specific to the fields. Recommendations for research include the effects of multi-nationality on crew interaction, development of tension within crews and between Mission Control, and prediction of critical phases in adaptation over time. Selection of interpersonally compatible crews, pre-mission team training and implementation of tools for self-monitoring of psychological parameters ensure that changes in mission requirements maximize crew performance.

Adaptation, Psychological↗
PubMed2005

Computer simulations of polymer chain structure and dynamics on a hypersphere in four-space.

There is a rapidly growing interest in performing computer simulations in a closed space, avoiding periodic boundary conditions. To extend the range of potential systems to include also macromolecules, we describe an algorithm for computer simulations of polymer chain molecules on S3, a hypersphere in four dimensions. In particular, we show how to generate initial conformations with a bond angle distribution given by the persistence length of the chain and how to calculate the bending forces for a molecule moving on S3. Furthermore, we discuss how to describe the shape of a macromolecule on S3, by deriving the radius of gyration tensor in this non-Euclidean space. The results from both Monte Carlo and Brownian dynamics simulations in the infinite dilution limit show that the results on S3 and in R3 coincide, both with respect to the size and shape as well as for the diffusion coefficient. All data on S3 can also be described by master curves by suitable scaling by the corresponding values in R3. We thus show how to extend the use of spherical boundary conditions, which are most effective for calculating electrostatic forces, to polymer chain molecules, making it possible to perform simulations on S3 also for polyelectrolyte systems.

Journal Article↗
PubMed1997

[Observation of changes of cardiovascular function during 2.5h HDT (-15 degrees) with sphygmogram method].

To understand the changes of cardiovascular functions in the initial stage of space flight, the changes in 19 healthy young men during 2.5h head down tilt (HDT) (15 degrees) were observed with CF-II cardiovascular function detecting and diagnosing equipment. The blood pressure and sphygmogram of left radial arterial were recorded in sedentary condition and at 10th, 30th, 60th, 90th, 120th and 140th minute of HDT. The results showed that changes of cardiovascular indices during HDT can be divided into acute regulation stage (< 1h) and the regulation stage (1-2.5 h); circulatory blood volume, stroke volume and cardiac output were increased, while heart rate, pre and after load of the heart, CVP, coronary circulatory function, blood pressure and systemic vascular resistance were decreased; the vagus feedback index increased and the regulation function of vasscule decreased. Most of the changes of cardiovascular indices as reflected in the sphygmogram are in consistent with the reported result in space flight or simulated micro-G, so the sphygmogram method might be applied to space medical research.

Aerospace Medicine↗
PubMed1994

Lipid peroxidation of plants under microgravity and its simulation.

In series of space experiments aboard the biosatellites "Cosmos 1887", "Bion 9", the orbital stations "Salut", "Mir" and under clinostating, changes of lipid peroxidation (LPO) and antioxidation activity (AOA) of Chlorella, Haplopappus tissue culture, wheat and pea roots were determined. The changes had a complex fluctuation character; three steps of response were established: LPO decreasing accompanied by AOA increase; stabilization LPO <==> AOA balance; secondary LPO activation. Most early and highly amplitude decreasing of LPO were fixed in mitochondria. The rate of response have been increased on multicellular level of plants organization.

Antioxidants↗
PubMed1992

Global approach to simulation: a gateway to long-term human presence in space.

The establishment of an autonomous European manned space capability is an objective set up by the ESA Council Meeting at the ministerial level, in 1985/1987. ESA's Long-Term Programme Office (LTPO), charged of the preparation of the programme for a European Manned Space Infrastructure (EMSI), started during 1988 to build up an intellectual framework in the domain of long-duration manned space missions. EMSI scope was eventually extended to embrace Moon/Mars missions and bases. Several exploratory studies on problems related to human factors in long-duration space missions were initiated by LTPO. The work of an ad-hoc group of experts (SIMIS Group) has been focused during 1989/1990 on the planning for simulation of such missions with a broad mandate, covering the physiological, psychological and operational aspects of long-duration exposure to microgravity and isolation/confinement. Preliminary results of SIMIS activities are reported. The HYDREMSI experiment, carried out in a terrestrial, analogous environment for 72 days during 1989, is described as an example of the envisaged simulations.

Astronauts↗
PubMed1999

Non-Boltzmann thermodynamic integration (NBTI) for macromolecular systems: relative free energy of binding of trypsin to benzamidine and benzylamine.

The relative free energies of binding of trypsin to two amine inhibitors, benzamidine (BZD) and benzylamine (BZA), were calculated using non-Boltzmann thermodynamic integration (NBTI). Comparison of the simulations with the crystal structures of both complexes, trypsin-BZD and trypsin-BZA, shows that NBTI simulations better sample conformational space relative to thermodynamic integration (TI) simulations. The relative binding free energy calculated using NBTI was much closer to the experimentally determined value than that obtained using TI. The error in the TI simulation was found to be primarily due to incorrect sampling of BZA's conformation in the binding pocket. In contrast, NBTI produces a smooth mutation from BZD to BZA using a surrogate potential, resulting in a much closer agreement between the inhibitors' conformations and the omit electron density maps. This superior agreement between experiment and simulation, of both relative binding free energy differences and conformational sampling, demonstrates NBTI's usefulness for free energy calculations in macromolecular simulations.

Benzamidines↗
PubMed1993

How consistent are molecular dynamics simulations? Comparing structure and dynamics in reduced and oxidized Escherichia coli thioredoxin.

In this study we have examined several parameters that can be used for checking the consistency and accuracy of protein structures and molecular dynamics simulations. This is done by comparing: (1) three X-ray structures of oxidized Escherichia coli thioredoxin (Trx-S2); (2) 14 NMR structures of reduced E. coli thioredoxin (Trx-(SH)2); and (3) 30 different simulations, 15 of Trx-S2 and 15 of Trx-(SH)2. The energy, the agreement with NOE data, the root-mean-square deviation between structures, and the surface characteristics of all these structures are analyzed. The 30 simulations, four water simulations, 20 standard vacuum simulations and six alternative vacuum simulations, are examined with respect to mobility, temperature factors and aromatic side-chain mobility. It is shown that although vacuum simulations may reproduce some parameters, all the features of a water simulation cannot be reproduced in any of these simulations. Several of the parameters described above are shown to be good for discriminating between an accurate and an inaccurate simulation. It is also shown that 100 ps is too short a time to obtain statistically certain temperature factors and correlation functions of aromatic side-chain motions. The results also suggest that performing ten 100 ps simulations spans the conformation space better than one 1 ns simulation.

Computer Simulation↗
PubMed2004

Simulation experiments of the effect of space environment on bacteriophage and DNA thin films.

The main goal of PUR experiment (phage and uracil response) is to examine and quantify the effect of specific space conditions on nucleic acid models. To achieve this an improved method was elaborated for the preparation of DNA and bacteriophage thin films. The homogeneity of the films was controlled by UV spectroscopy and microscopy. To provide experimental evidence for the hypothesis that interplanetary transfer of the genetic material is possible, phage T7 and isolated T7 DNA thin films have been exposed to selected space conditions: intense UVC radiation (lambda=254 nm) and high vacuum (10(-4) Pa). The effects of DNA hydration, conformation and packing on UV radiation damage were examined. Characteristic changes in the absorption spectrum, in the electrophoretic pattern of DNA and the decrease of the amount of PCR products have been detected indicating the photodamage of isolated and intraphage DNA.

Bacteriophage T7↗
PubMed2006

Accommodating space, time and randomness in network simulation.

Interest in the possibility of dynamically simulating complex cellular processes has escalated markedly in recent years. This interest has been fuelled by three factors: the generally accepted value in understanding living processes as integrated systems; the dramatic increase in computational capability; and the availability of new or improved technology for making the quantitative measurements that are needed to drive and validate cellular simulations. Between the extremes of atom-scale and organism-scale simulation is a vast middle-ground requiring simulation strategies that are capable of dealing with a range of spatial, temporal and molecular abundance scales that are crucial for a comprehensive understanding of integrative cell biology. Although at an early stage, methodological improvements and the development of computational platforms provide some hope that simulations will emerge that can bridge the gap between network models and the true operation of the cell as a complex machine.

Animals↗