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  • 1
    Electronic Resource
    Electronic Resource
    Thermodynamic and kinetic studies of a stoichiometric model of energetic metabolism under starvation conditions (1990)
    Oxford, UK : Blackwell Publishing Ltd
    FEMS microbiology letters 66 (1990), S. 0 
    Details
    ISSN: 1574-6968
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Biology
    Notes: Abstract A stoichiometric model of anaerobic glycolysis is presented and the influence on its dynamics by the ATP-consuming membrane transport processes and substrate input rate are studied. The model is represented by a system of four ODE (ordinary differential equations), mass conservation equations and functions of state variables, such as thermodynamic efficiency. A low substrate input rate provokes damped oscillations while a high enrgy load determines sustained oscillations in all the metabolites and in thermodynamic efficiency. Due to the lack of linearity between fluxes and forces in the oscillatory region it may be stated that oscillations appear when the system is kinetically controlled.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1111/j.1574-6968.1990.tb04006.x
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  • 2
    Electronic Resource
    Electronic Resource
    An allometric interpretation of the spatio-temporal organization of molecular and cellular processes (1993)
    Springer
    Molecular and cellular biochemistry 120 (1993), S. 1-13 
    Details
    ISSN: 1573-4919
    Keywords: dynamical organization ; levels of organization ; allometry ; bistability ; oscillations ; asymmetry changes
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Chemistry and Pharmacology , Medicine
    Notes: Summary Different levels of organization distinguished by characteristics spatial dimensions, Ec, and relaxation times, Tr, of biological processes ranging from electron transport in energy transduction to growth of microbial and plant cells, are shown to be related through a relation that may be interpreted as allometric and characterized by two different slopes. Processes, at levels of organization occurring in spatial dimensions of micrometers and relaxing in the order of minutes, delimit a ‘transition point’ between the two curves, that we interpret as a limit for the emergence of macroscopic coherence. The characteristic spatial dimension, Ec, and the relaxation time, Tr, contain dynamical information about the processes occurring at a given level of organization. When a steady state of a biological process at a certain level of organization becomes unstable, the system undergoes a transition to another level of organization. To exemplify the appearance of macroscopic order at levels of organization further from the ‘transition point’ we present in this report various experimental systems involving many levels of organization allometrically related that exhibit different kinds of self-organized behavior, i.e. bistability, oscillations, changes in (a)symmetry.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00925979
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  • 3
    Electronic Resource
    Electronic Resource
    Altered topoisomerase activities may be involved in the regulation of DNA supercoiling in aerobic-anaerobic transitions inEscherichia coli (1993)
    Springer
    Molecular and cellular biochemistry 126 (1993), S. 115-124 
    Details
    ISSN: 1573-4919
    Keywords: DNA supercoiling ; DNA topoisomerases ; [ATP]/[ADP] ratio ; aerobic anaerobic transitions ; Escherichia coli
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Chemistry and Pharmacology , Medicine
    Notes: Abstract This study uncovers a new mechanism of regulation of DNA supercoiling operativein vivo upon an aerobic-anaerobic transition inEscherichia coli. Exponentially growing aerobic batch cultures were subjected to a shift to anaerobic conditions. The ratio [ATP]/[ADP] remained essentially constant at 8.5 in the aerobic culture and after a transition to anaerobiosis while DNA supercoiling increased noticeably upon anaerobiosis. This result indicated that the mechanism of regulation of DNA supercoiling by the [ATP]/[ADP] ratio was not operative. The increase in DNA supercoiling was followed by a large decrease in the DNA-relaxing activity of topoisomerase I while gyrase activity remained relatively constant. This decrease in the activity of topoisomerase I is likely to be responsible for the increase in DNA supercoiling.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00925689
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  • 4
    Electronic Resource
    Electronic Resource
    Thermodynamic evaluation of energy metabolism in mixed substrate catabolism: Modeling studies of stationary and oscillatory states (1991)
    New York, NY [u.a.] : Wiley-Blackwell
    Biotechnology and Bioengineering 37 (1991), S. 197-204 
    Details
    ISSN: 0006-3592
    Keywords: Chemistry ; Biochemistry and Biotechnology
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Biology , Process Engineering, Biotechnology, Nutrition Technology
    Notes: Thermodynamic and kinetic calculations were performed in a model of mixed substrate metabolism. The model simulates the catabolic breakdown of a first substrate, glucose (S1), in the presence of a second substrate, formate (S2), which acts as an additional source of free energy. The principal results obtained with different relative rates of uptake of S2 allow to predict and interpret the following experimental observations: (1) the existence of increased ATP yields by mixed substrate utilization with a maximum ATP yield and optimum input (or molar) ratio for both substrates; (2) a greater assimilation of S1 which may be interpreted as a decreasing fraction of energy required for assimilation; (3) a decrease in ATP yields due to increasing energy demand for transport; (4) an increased assimilation of the carbon source (S1) as a function of increasing inputs of the additional energy source; (5) thermodynamic efficiency (η) defined as the ratio between the output power of ATP synthesis and the input catabolic power, increases for S2/S1 ratios ranging between 0.08 and 2 while for ratios higher than two a slight decrease of η was noticed; and (6) the observed maximum in ATP yield for optimum molar ratio of the two substrates corresponds to high η predicting that higher biomass yields may be obtained through a variable, high, η by chanelling fluxes through catabolic pathways with different ATP yields. During oscillatory behavior, maxima in fluxes were almost coincident with maxima in forces. Thus, the pattern of dissipation was not so advantageous as in the single substrate model under starvation conditions.
    Additional Material: 10 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/bit.260370302
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    Paper (German National Licenses)
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