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  • 1
    Electronic Resource
    Electronic Resource
    A non-equilibrium thermodynamics model of reconstituted Ca2+-ATPase (1998)
    Springer
    European biophysics journal 27 (1998), S. 255-262 
    Details
    ISSN: 1432-1017
    Keywords: Key words Coupling stoichiometry ; Electrogenicity ; Slip ; Calcium pumping ; Proton ejection
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Physics
    Notes: Abstract A non-equilibrium thermodynamics (NET) model describing the action of completely coupled or `slipping' reconstituted Ca2+-ATPase is presented. Variation of the coupling stoichiometries with the magnitude of the electrochemical gradients, as the ATPase hydrolyzes ATP, is an indication of molecular slip. However, the Ca2+ and H+ membrane-leak conductances may also be a function of their respective gradients. Such non-ohmic leak typically yields `flow-force' relationships that are similar to those that are obtained when the pump slips; hence, caution needs to be exercised when interpreting data of Ca2+-ATPase-mediated fluxes that display a non-linear dependence on the electrochemical proton (Δµ˜H) and/or calcium gradients (Δµ˜Ca). To address this issue, three experimentally verifiable relationships differentiating between membrane leak and enzymic slip were derived. First, by measuring Δµ˜H as a function of the rate of ATP hydrolysis by the enzyme. Second, by measuring the overall `efficiency' of the pump as a function of Δµ˜H. Third, by measuring the proton ejection rate by the pump as a function of its ATP hydrolysis rate.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/s002490050132
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  • 2
    Electronic Resource
    Electronic Resource
    Catabolite repression by glucose 6-phosphate, gluconate and lactose in Escherichia coli (1997)
    Oxford UK : Blackwell Science Ltd
    Molecular microbiology 24 (1997), S. 0 
    Details
    ISSN: 1365-2958
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Biology , Medicine
    Notes: While catabolite repression by glucose has been studied extensively and is understood in large detail in Enterobacteriaceae, catabolite repression by carbohydrates that are not transported by the phosphotransferase system (PTS) has always remained an enigma. Examples of non-PTS carbohydrates that cause catabolite repression in Escherichia coli are gluconate, lactose and glucose 6-phosphate. In this article it is shown that enzyme IIAGlc of the PTS is not involved in catabolite repression by these carbon sources. Carbon sources that caused strong catabolite repression of β-galactosidase lowered the concentration of both cAMP and the cAMP receptor protein (CRP). A strong correlation was found between the amounts of cAMP and CRP and the strength of the repression. The levels of cAMP and CRP were modulated in various ways. Neither overproduction of CRP nor an increased cAMP concentration could completely relieve the repression by glucose 6-phosphate, lactose and gluconate. Simultaneously increasing the cAMP and the CRP levels was lethal for the cells. In a mutant expressing a constant amount of cAMP-independent CRP* protein, catabolite repression was absent. The same was found in a mutant in which lac transcription is independent of cAMP/CRP. These results, combined with the fact that both the cAMP and the CRP levels are lowered by glucose 6-phosphate, lactose and gluconate, lead to the conclusion that the decreased cAMP and CRP levels are the cause of catabolite repression by these non-PTS carbon sources.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1046/j.1365-2958.1997.3991761.x
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  • 3
    Electronic Resource
    Electronic Resource
    A functional genomics strategy that uses metabolome data to reveal the phenotype of silent mutations (2001)
    [s.l.] : Nature America Inc.
    Nature biotechnology 19 (2001), S. 45-50 
    Details
    ISSN: 1546-1696
    Source: Nature Archives 1869 - 2009
    Topics: Biology , Process Engineering, Biotechnology, Nutrition Technology
    Notes: [Auszug] A large proportion of the 6,000 genes present in the genome of Saccharomyces cerevisiae, and of those sequenced in other organisms, encode proteins of unknown function. Many of these genes are “silent,” that is, they show no overt phenotype, in terms of growth rate or other fluxes, ...
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1038/83496
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  • 4
    Electronic Resource
    Electronic Resource
    High-affinity glucose uptake in Saccharomyces cerevisiae is not dependent on the presence of glucose-phosphorylating enzymes (1996)
    New York, NY [u.a.] : Wiley-Blackwell
    Yeast 12 (1996), S. 439-447 
    Details
    ISSN: 0749-503X
    Keywords: transport ; glucose uptake ; Saccharomyces cerevisiae ; yeast ; rapid kinetics ; Life Sciences ; Life Sciences (general)
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Biology
    Notes: Glucose uptake in Saccharomyces cerevisiae is believed to consist of two kinetically distinguishable components, the affinity of which is modulated during growth on glucose. It has been reported that triple hexose-kinase deletion mutants do not exhibit high-affinity glucose uptake. This raises the question of whether and how high-affinity glucose uptake is related to the presence of glucose-phosphorylating enzymes. In this study the kinetics of glucose uptake in both wild-type cells and cells of hexose-kinase deletion mutants, grown on either glycerol or galactose, were determined using a rapid-uptake method. In wild-type cells glucose uptake measured over either 5 s or 200 ms exhibited high affinity. In contrast, in cells of hexose-kinase deletion mutants the apparent affinity of glucose uptake was dependent on the time scale during which uptake was measured. Measurements on the 5-s scale showed apparent low-affinity uptake whereas measurements on the 200-ms scale showed high-affinity uptake. The affinity and maximal rate of the latter were comparable to those in wild-type cells.Using a simple model for a symmetrical facilitator, it was possible to simulate the experimentally determined relation between apparent affinity and the time scale used.The results suggest that high-affinity glucose transport is not necessarily dependent on the presence of glucose-phosphorylating enzymes. Apparent low-affinity uptake kinetics can arise as a consequence of an insufficient rate of removal of intracellular free glucose by phosphorylation.This study underlines the need to differentiate between influences of the translocator and of metabolism on the apparent kinetics of sugar uptake in yeast.
    Additional Material: 5 Ill.
    Type of Medium: Electronic Resource
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    Paper (German National Licenses)
  • 5
    Electronic Resource
    Electronic Resource
    Sustained oscillations in free-energy state and hexose phosphates in yeast (1996)
    New York, NY [u.a.] : Wiley-Blackwell
    Yeast 12 (1996), S. 731-740 
    Details
    ISSN: 0749-503X
    Keywords: oscillation ; glycolysis ; yeast ; Saccharomyces cerevisiae ; intracellular metabolites ; Life Sciences ; Life Sciences (general)
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Biology
    Notes: In a population of intact cells of the yeast Saccharomyces cerevisiae the dynamics of glycolytic metabolism were investigated under the condition of sustained oscillations. At 5-s intervals cells were quenched in -40°C methanol, extracted and the intracellular concentrations of glycolytic metabolites, adenine nucleotides and phosphate were analysed. Oscillations were found for the glycolytic intermediates glucose 6-phosphate, fructose 6-phosphate and fructose 1,6-bisphosphate. At variance with earlier reports on transient glycolytic oscillations, some intermediates further down the glycolytic pathway did not oscillate significantly, even though NADH did. In addition, the adenylate energy charge and the free energy of ATP hydrolysis oscillated significantly. Dynamic coupling through the latter may be responsible for this effective compartmentation of glycolytic dynamics.
    Additional Material: 6 Ill.
    Type of Medium: Electronic Resource
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    Paper (German National Licenses)
  • 6
    Electronic Resource
    Electronic Resource
    Respiratory inhibitors affect incorporation of glucose into Saccharomyces cerevisiae cells, but not the activity of glucose transport (1994)
    New York, NY [u.a.] : Wiley-Blackwell
    Yeast 10 (1994), S. 1553-1558 
    Details
    ISSN: 0749-503X
    Keywords: Glucose-transport ; rapid-kinetics ; S. cerevisiae ; Life and Medical Sciences ; Genetics
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Biology
    Notes: Incubation of starved galactose-grown S. cerevisiae cells with cyanide reduced glucose uptake as measured over a 5-s period. The Vmax for glucose uptake was decreased by over a factor of two but the apparent affinity for glucose doubled. When measured in the sub-second time scale, however, there was no significant inhibition of glucose uptake, by cyanide, up to 200-ms, clearly demonstrating that, in cyanide treated cells, glucose uptake was not linear for the first 5-s.After a 200-ms exposure of untreated cells to radio-labelled glucose, less than 10% of the intracellular label resided in soluble uncharged compounds. In cyanide-treated cells up to 43% of the labelled compounds were uncharged, with a concurrent reduction of intracellular label residing in anionic compounds. The results suggest that, in the presence of 10 mM cyanide when respiration is inhibited, a reduction in the cellular ATP concentration causes a reduction in hexose-kinase activity which results in an accumulation of internal free glucose, which in turn causes a reduction in net glucose transport.
    Additional Material: 3 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/yea.320101204
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