1,024 research outputs found
Low Dimensional Strange Attractors in Epidemics of Childhood Diseases in Copenhagen, Denmark
No full textIs a constant low-entropy process at the root of glycolytic oscillations?
Full text linkWe measured temporal oscillations in thermodynamic variables such as temperature, heat flux, and cellular volume in suspensions of non-dividing yeast cells which exhibit temporal glycolytic oscillations. Oscillations in these variables have the same frequency as oscillations in the activity of intracellular metabolites, suggesting strong coupling between them. These results can be interpreted in light of a recently proposed theoretical formalism in which isentropic thermodynamic systems can display coupled oscillations in all extensive and intensive variables, reminiscent of adiabatic waves. This interpretation suggests that oscillations may be a consequence of the requirement of living cells for a constant low-entropy state while simultaneously performing biochemical transformations, i.e., remaining metabolically active. This hypothesis, which is in line with the view of the cellular interior as a highly structured and near equilibrium system where energy inputs can be low and sustain regular oscillatory regimes, calls into question the notion that metabolic processes are essentially dissipative.Fil: Thoke, Henrik Seir. University of Southern Denmark; Dinamarca. International and Interdisciplinary Research Network; DinamarcaFil: Olsen, Lars F.. International and Interdisciplinary Research Network; Dinamarca. University of Southern Denmark; DinamarcaFil: Duelund, Lars. University of Southern Denmark; Dinamarca. International and Interdisciplinary Research Network; DinamarcaFil: Stock, R. P.. International and Interdisciplinary Research Network; DinamarcaFil: Heimburg, Thomas. Universidad de Copenhagen; DinamarcaFil: Bagatolli, Luis Alberto. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Córdoba. Instituto de Investigación Médica Mercedes y Martín Ferreyra. Universidad Nacional de Córdoba. Instituto de Investigación Médica Mercedes y Martín Ferreyra; Argentina. International and Interdisciplinary Research Network; Dinamarc
Glycolytic oscillations and intracellular K+ concentration are strongly coupled in the yeast Saccharomyces cerevisiae
No full textWe measured temporal oscillations of intracellular K+ concentration in yeast cells exhibiting glycolytic oscillations using fluorescence spectroscopy and microscopy methods. These oscillations showed the same period as those of glycolytic metabolites (NADH, ATP), indicating a strong coupling between them. We experimentally ruled out that oscillations originate in extra- or intracellular K+ fluxes and conclude that these oscillations arise from fluctuations in free and adsorbed states of K+ in the cell interior. Oscillations in K+ showed a strong dependence on ATP and the organization of the cell cytoskeleton. Our results challenge the widely held view that intracellular K+ predominantly exists in a free state. They can, however, be productively understood in terms of Gilbert Ling's Association-Induction hypothesis.Fil: Olsen, Lars F.. University of Southern Denmark; Dinamarca. Memphys; DinamarcaFil: Stock, Roberto P.. Memphys; DinamarcaFil: Bagatolli, Luis Alberto. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Córdoba. Instituto de Investigación Médica Mercedes y Martín Ferreyra. Universidad Nacional de Córdoba. Instituto de Investigación Médica Mercedes y Martín Ferreyra; Argentina. Memphys; Dinamarca. Universidad Nacional de Córdoba. Facultad de Ciencias Químicas. Departamento de Química Biológica; Argentin
Coupled response of membrane hydration with oscillating metabolism in live cells: An alternative way to modulate structural aspects of biological membranes?
Full text linkWe propose that active metabolic processes may regulate structural changes in biological membranes via the physical state of cell water. This proposition is based on recent results obtained from our group in yeast cells displaying glycolytic oscillations, where we demonstrated that there is a tight coupling between the oscillatory behavior of glycolytic metabolites (ATP, NADH) and the extent of the dipolar relaxation of intracellular water, which oscillates synchronously. The mechanism we suggest involves the active participation of a polarized intracellular water network whose degree of polarization is dynamically modulated by temporal ATP fluctuations caused by metabolism with intervention of a functional cytoskeleton, as conceived in the long overlooked association-induction hypothesis (AIH) of Gilbert Ling. Our results show that the polarized state of intracellular water can be propagated from the cytosol to regions containing membranes. Since changes in the extent of the polarization of water impinge on its chemical activity, we hypothesize that metabolism dynamically controls the local structure of cellular membranes via lyotropic effects. This hypothesis offers an alternative way to interpret membrane related phenomena (e.g., changes in local curvature pertinent to endo/exocytosis or dynamical changes in membranous organelle structure, among others) by integrating relevant but mostly overlooked physicochemical characteristics of the cellular milieu.Fil: Bagatolli, Luis Alberto. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Córdoba. Instituto de Investigación Médica Mercedes y Martín Ferreyra. Universidad Nacional de Córdoba. Instituto de Investigación Médica Mercedes y Martín Ferreyra; ArgentinaFil: Stock, Roberto P.. International and Interdisciplinary Research Network; DinamarcaFil: Olsen, Lars F.. University Of Southern Denmark; Dinamarc
Routes to chaos in the peroxidase-oxidase reaction. 2. The fat torus scenario
No full textExperimental studies [Hauser, M. J. B.; Olsen, L. F. J. Chem. Soc., Faraday Trans. 1996, 92, 2857-2863] of the peroxidase-oxidase (PO) reaction at pH values in excess of 5.4 suggest the existence of narrow regions of complex dynamics between adjacent mixed-mode oscillations (MMOs) that occur in period-adding sequences. Previously [Hauser, M. J. B.; Olsen, L. F.; Bronnikova, T. V.; Schaffer, W. M. J. Phys. Chem. B 1997, 101, 5075-5083], it was argued that both the period-adding sequences and the transitional regions between neighboring MMOs are predictable by a detailed model of the reaction called BFSO [Bronnikova, T. V.; Fed'kina, V. R.; Schaffer, W. M.; Olsen, L. F. J. Phys. Chem. 1995, 99, 9309-9312]. In the present paper, we study the transitional regions via computer simulation. Our investigations indicate that the motion therein may be periodic, quasiperiodic, or chaotic. In greater detail, we observe a quasiperiodic route to chaos whereby period-doubled cycles give rise to doubled tori that, in turn, undergo homoclinic bifurcations to chaos. Because the latter transitions are a consequence of progressive fattening of the tori, we propose calling this scenario the "fat torus" route to chaos, and the homoclinic bifurcations "fat torus" bifurcations (FTBs). The numerical results are qualitatively consistent with the experimental findings reported to date. FTBs and the resultant period-doubled, fractal tori may provide a criterion for discriminating among alternative models of the PO reaction.</p
Effect of macromolecular crowding on the kinetics of glycolytic enzymes and the behaviour of glycolysis in yeast
Full text linkWater is involved in all aspects of biological activity, both as a solvent and as a reactant. It is hypothesized that intracellular water is in a highly structured state due to the high concentrations of macromolecules in the cell and that this may change the activity of intracellular enzymes due to altered binding affinities and allosteric regulations. Here we first investigate the kinetics of two glycolytic enzymes in artificially crowded aqueous solutions and show that crowding does indeed change their kinetics. Based on our kinetic measurements we propose a new model of oscillating glycolysis that instead of Michaelis-Menten or Monod-Wyman-Changeux kinetics uses the Yang-Ling adsorption isotherm introduced by G. Ling in the frame of the Association-Induction (AI) hypothesis. Using this model, we can reproduce previous experimental observations of the coupling of glycolytic oscillations and intracellular water dynamics, e.g., (i) during the metabolic oscillations, the latter variable oscillates in phase with ATP activity, and (ii) the emergence of glycolytic oscillations largely depends on the extent of intracellular water dipolar relaxation in cells in the resting state. Our results support the view that the extent of intracellular water dipolar relaxation is regulated by the ability of cytoplasmic proteins to polarize intracellular water with the assistance of ATP, as suggested in the AI hypothesis. This hypothesis may be relevant to the interpretation of many other biological oscillators, including cell signalling processes.Fil: Thoke, Henrik S.. University Of Southern Denmark; DinamarcaFil: Bagatolli, Luis Alberto. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Córdoba. Instituto de Investigación Médica Mercedes y Martín Ferreyra. Universidad Nacional de Córdoba. Instituto de Investigación Médica Mercedes y Martín Ferreyra; ArgentinaFil: Olsen, Lars F.. University Of Southern Denmark; Dinamarc
On simultaneous local dimension functions of subsets of Rd
No full textDate of Acceptance: 04/05/2015For a subset E ⊑ Rd and x ∈ Rd, the local Hausdorff dimension function of E at x and the local packing dimension function of E at x are defined by (Formula presented.) where dimH and dimP denote the Hausdorff dimension and the packing dimension, respectively. In this note we give a short and simple proof showing that for any pair of continuous functions f,g: Rd → [0, d] with f ≤ g, it is possible to choose a set E that simultaneously has f as its local Hausdorff dimension function and g as its local packing dimension function.Peer reviewe
The dynamics of intracellular water constrains glycolytic oscillations in Saccharomyces cerevisiae
Full text linkWe explored the dynamic coupling of intracellular water with metabolism in yeast cells. Using the polarity-sensitive probe 6-acetyl-2-dimethylaminonaphthalene (ACDAN), we show that glycolytic oscillations in the yeast S. cerevisiae BY4743 wild-type strain are coupled to the generalized polarization (GP) function of ACDAN, which measures the physical state of intracellular water. We analysed the oscillatory dynamics in wild type and 24 mutant strains with mutations in many different enzymes and proteins. Using fluorescence spectroscopy, we measured the amplitude and frequency of the metabolic oscillations and ACDAN GP in the resting state of all 25 strains. The results showed that there is a lower and an upper threshold of ACDAN GP, beyond which oscillations do not occur. This critical GP range is also phenomenologically linked to the occurrence of oscillations when cells are grown at different temperatures. Furthermore, the link between glycolytic oscillations and the ACDAN GP value also holds when ATP synthesis or the integrity of the cell cytoskeleton is perturbed. Our results represent the first demonstration that the dynamic behaviour of a metabolic process can be regulated by a cell-wide physical property: the dynamic state of intracellular water, which represents an emergent property.Fil: Thoke, Henrik S.. Center for Biomembrane Physics; Dinamarca. University of Southern Denmark; DinamarcaFil: Thorsteinsson, Sigmundur. University of Southern Denmark; DinamarcaFil: Stock, Roberto P.. University of Southern Denmark; DinamarcaFil: Bagatolli, Luis Alberto. Consejo Nacional de Investigaciones Científicas y Técnicas; Argentina. Center for Biomembrane Physics; Dinamarca. Yachay EP and Yachay Tech; EcuadorFil: Olsen, Lars F.. Center for Biomembrane Physics; Dinamarca. University of Southern Denmark; Dinamarc
Lars von Trier as Ivan Karamazov
No full textСтатья поступила в редакцию 13.11.2014 г.Статья посвящена творчеству современного датского режиссера и сценариста Ларса
фон Триера. Выдвигается и обосновывается гипотеза феномена близости его кинематографа художественному миру Ф. М. Достоевского. Многочисленные параллели трактуются как следствие того, что фон Триер в своих фильмах воспроизводит то мирочувствование, которое Достоевский воплотил в образе Ивана Карамазова.The article is devoted to the creative work of the contemporary Danish director and scriptwriter Lars von Trier. The author puts forward and substantiates a hypothesis about the kindred character of his cinematographic work to the artistic world of F. M. Dostoyevsky. The multiple parallels are interpreted as a consequence
of von Trier’s reproduction of the worldview that Dostoyevsky reflected in the image of his Ivan Karamazov
Artificial photosynthesis: Hybrid systems
No full textOxidoreductases are promising catalysts for organic synthesis. To sustain their catalytic cycles they require efficient supply with redox equivalents. Today classical biomimetic approaches utilizing natural electron supply chains prevail but artificial regeneration approaches bear the promise of simpler and more robust reaction schemes. Utilizing visible light can accelerate such artificial electron transport chains and even enable thermodynamically unfeasible reactions such as the use of water as reductant. This contribution critically summarizes the current state of the art in photoredoxbiocatalysis (i.e. light-driven biocatalytic oxidation and reduction reactions).Accepted Author ManuscriptBT/Biocatalysi
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