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  • 1
    Electronic Resource
    Electronic Resource
    Linear relations between proton current and pH gradient in bacteriorhodopsin liposomes (1981)
    s.l. : American Chemical Society
    Biochemistry 20 (1981), S. 5114-5123 
    Details
    ISSN: 1520-4995
    Source: ACS Legacy Archives
    Topics: Biology , Chemistry and Pharmacology
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1021/bi00521a004
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  • 2
    Electronic Resource
    Electronic Resource
    Forms of the chemotactic adenosine cyclic 3',5'-phosphate receptor in isolated Dictyostelium discoideum membranes and interconversions induced by guanine nucleotides (1986)
    s.l. : American Chemical Society
    Biochemistry 25 (1986), S. 1314-1320 
    Details
    ISSN: 1520-4995
    Source: ACS Legacy Archives
    Topics: Biology , Chemistry and Pharmacology
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1021/bi00354a019
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  • 3
    Electronic Resource
    Electronic Resource
    Inducer exclusion in Escherichia coli by non-PTS substrates: the role of the PEP to pyruvate ratio in determining the phosphorylation state of enzyme IIAGlc (1998)
    Oxford BSL : Blackwell Science Ltd
    Molecular microbiology 30 (1998), S. 0 
    Details
    ISSN: 1365-2958
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Biology , Medicine
    Notes: The main mechanism causing catabolite repression in Escherichia coli is the dephosphorylation of enzyme IIAGlc, one of the enzymes of the phosphoenolpyruvate:carbohydrate phosphotransferase system (PTS). The PTS is involved in the uptake of a large number of carbohydrates that are phosphorylated during transport, phosphoenolpyruvate (PEP) being the phosphoryl donor. Dephosphorylation of enzyme IIAGlc causes inhibition of uptake of a number of non-PTS carbon sources, a process called inducer exclusion. In this paper, we show that dephosphorylation of enzyme IIAGlc is not only caused by the transport of PTS carbohydrates, as has always been thought, and that an additional mechanism causing dephosphorylation exists. Direct monitoring of the phosphorylation state of enzyme IIAGlc also showed that many carbohydrates that are not transported by the PTS caused dephosphorylation during growth. In the case of glucose 6-phosphate, it was shown that transport and the first metabolic step are not involved in the dephosphorylation of enzyme IIAGlc, but that later steps in the glycolysis are essential. Evidence is provided that the [PEP]–[pyruvate] ratio, the driving force for the phosphorylation of the PTS proteins, determines the phosphorylation state of enzyme IIAGlc. The implications of these new findings for our view on catabolite repression and inducer exclusion are discussed.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1046/j.1365-2958.1998.01053.x
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  • 4
    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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  • 5
    Electronic Resource
    Electronic Resource
    Autoregulation of lactose uptake through the LacYpermease by enzyme IIAGlc of the PTS in Escherichia coli K-12 (1999)
    Oxford BSL : Blackwell Science Ltd
    Molecular microbiology 31 (1999), S. 0 
    Details
    ISSN: 1365-2958
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Biology , Medicine
    Notes: Bacterial growth on one or more carbon sources requires careful control of the uptake and metabolism of these carbon sources. In Escherichia coli, the phosphorylation state of enzyme IIAGlc of the phosphoenolpyruvate:carbohydrate phosphotransferase system (PTS) is involved in this control in two ways. The unphosphorylated form of IIAGlc causes ‘inducer exclusion’, the inhibition of uptake of a number of non-PTS carbon sources, including lactose uptake by the lactose permease. The phosphorylated form of enzyme IIAGlc probably activates adenylate cyclase. In cells growing on lactose, enzyme IIAGlc was approximately 50% dephosphorylated, suggesting that lactose could inhibit its own uptake. This inhibition could be demonstrated by comparing lactose uptake rates in the wild-type strain and in a mutant in which the lactose carrier was insensitive to inducer exclusion. In this deregulated mutant strain, lactose was consumed much faster, and large amounts of glucose were excreted. It was shown that enzyme IIAGlc was dephosphorylated more strongly and that the cAMP level was lower in the mutant, most probably causing the observed decrease in lac expression level. When the lac expression level in the mutant strain was increased to that of the parent strain by adding exogenous cAMP, growth on lactose was slower, suggesting that enzyme IIAGlc-mediated inhibition of lactose uptake and downregulation of the lac expression level protected the cells against excessive lactose influx. An even stronger increase in the lac expression level in a mutant lacking enzyme IIAGlc caused complete growth arrest. We conclude that the autoregulatory mechanism that controls lactose uptake is an important mechanism for the cells in adjusting the uptake rate to their metabolic capacity.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1046/j.1365-2958.1999.01319.x
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  • 6
    Electronic Resource
    Electronic Resource
    Inducer exclusion by glucose 6-phosphate in Escherichia coli (1998)
    Oxford BSL : Blackwell Science Ltd, UK
    Molecular microbiology 28 (1998), S. 0 
    Details
    ISSN: 1365-2958
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Biology , Medicine
    Notes: The main mechanism causing catabolite repression by glucose and other carbon sources transported by the phosphotransferase system (PTS) in Escherichia coli involves dephosphorylation of enzyme IIAGlc as a result of transport and phosphorylation of PTS carbohydrates. Dephosphorylation of enzyme IIAGlc leads to ‘inducer exclusion’: inhibition of transport of a number of non-PTS carbon sources (e.g. lactose, glycerol), and reduced adenylate cyclase activity. In this paper, we show that the non-PTS carbon source glucose 6-phosphate can also cause inducer exclusion. Glucose 6-phosphate was shown to cause inhibition of transport of lactose and the non-metabolizable lactose analogue methyl-β-D-thiogalactoside (TMG). Inhibition was absent in mutants that lacked enzyme IIAGlc or were insensitive to inducer exclusion because enzyme IIAGlc could not bind to the lactose carrier. Furthermore, we showed that glucose 6-phosphate caused dephosphorylation of enzyme IIAGlc. In a mutant insensitive to enzyme IIAGlc-mediated inducer exclusion, catabolite repression by glucose 6-phosphate in lactose-induced cells was much weaker than that in the wild-type strain, showing that inducer exclusion is the most important mechanism contributing to catabolite repression in lactose-induced cells. We discuss an expanded model of enzyme IIAGlc-mediated catabolite repression which embodies repression by non- PTS carbon sources.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1046/j.1365-2958.1998.00833.x
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  • 7
    Electronic Resource
    Electronic Resource
    Guanine nucleotides modulate the function of chemotactic cyclic AMP receptors inDictyostelium discoideum (1985)
    Springer
    Molecular and cellular biochemistry 67 (1985), S. 119-124 
    Details
    ISSN: 1573-4919
    Keywords: cAMP receptor ; Dictyostelium discoideum ; G-protein ; guanine nucleotides ; slime mould
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Chemistry and Pharmacology , Medicine
    Notes: Summary Guanosine di- and triphosphates specifically decrease the affinity of chemotactic cAMP receptors in isolatedDictyostelium discoideum membranes. The K0.5 was increased from 50 nM to 150 nM. Receptors were shown to be heterogeneous in dissociation kinetics. In the absence of guanine nucleotides three dissociation processes could be resolved, having first order rate constants of 8.7 x 10−4, 1.3 X 10−2, and higher than 0.1 s−1. Guanine nucleotides decreased the affinity for cAMP by transforming the slowest dissociating receptor form (KD is 8 nM) to forms dissociating more rapidly. Our data indicate that a guanine nucleotide binding protein (G-protein) is involved in the transduction of the cAMP signal inD. discoideum.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF02370170
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  • 8
    Electronic Resource
    Electronic Resource
    Bacteriorhodopsin in liposomes: Quantitative evaluation of ΔpH changes induced by variations of light intensity and conductivity parameters (1981)
    Springer
    The journal of membrane biology 60 (1981), S. 95-104 
    Details
    ISSN: 1432-1424
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Chemistry and Pharmacology
    Notes: Summary A description of ion movement and energy transduction in terms of a kinetic variant of nonequilibrium thermodynamics was subjected to experimental tests in bacteriorhodopsin liposomes. The effects of variation of light intensity, proton permeability, proton-potassium ion exchange activity, and potassium ion permeability on the steadystate pH gradient were in quantitative agreement with the predictions of the theoretical description. It is suggested that the theoretical description will be useful in other, more complex systems to gain detailed information about their energy transduction and ion permeation properties.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF01870413
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  • 9
    Electronic Resource
    Electronic Resource
    Two (completely) rate-limiting steps in one metabolic pathway? The resolution of a paradox using bacteriorhodopsin liposomes and the control theory (1984)
    Springer
    Bioscience reports 4 (1984), S. 23-31 
    Details
    ISSN: 1573-4935
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Chemistry and Pharmacology
    Notes: Abstract Proton pumping by bacteriorhodopsin and chargecompensating ion movement can both and simultaneously behave as the rate-limiting step in light-driven proton uptake into bacteriorhodopsin liposomes. This apparently excessive control exerted on the net proton influx is possible because of the negative (−1) ‘control coefficient’ of the net proton influx with respect to the proton leaks. Furthermore, the property of bacteriorhodopsin that it is inhibited by the membrane potential is responsible for the transfer of part of the control on the net proton influx from the first, irreversible, step in the pathway (i.e. bacteriorhodopsin) to the second, reversible, step ( i.e., charge-compensating ion movement).
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF01120820
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  • 10
    Electronic Resource
    Electronic Resource
    Guanylate cyclase activity in permeabilized Dictyostelium discoideum cells (1996)
    New York, N.Y. : Wiley-Blackwell
    Journal of Cellular Biochemistry 60 (1996), S. 411-423 
    Details
    ISSN: 0730-2312
    Keywords: Dictyostelium ; guanylate cyclase ; cGMP ; chemotaxis ; GTP ; adaptation ; Life and Medical Sciences ; Cell & Developmental Biology
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Biology , Chemistry and Pharmacology , Medicine
    Notes: Dictyostelium discoideum cells respond to chemoattractants by transient activation of guanylate cyclase. Cyclic GMP is a second messenger that transduces the chemotactic signal. We used an electropermeabilized cell system to investigate the regulation of guanylate cyclase. Enzyme activity in permeabilized cells was dependent on the presence of a nonhydrolysable GTP analogue (e.g., GTPγS), which could not be replaced by GTP, GDP, or GMP. After the initiation of the guanylate cyclase reaction in permeabilized cells only a short burst of activity is observed, because the enzyme is inactivated with a t1.2 of about 15 s. We show that inactivation is not due to lack of substrate, resealing of the pores in the cell membrane, product inhibition by cGMP, or intrinsic instability of the enzyme. Physiological concentrations of Ca2+ ions inhibited the enzyme (half-maximal effect at 0.3 μM), whereas InsP3 had no effect. Once inactivated, the enzyme could only be reactivated after homogenization of the permeabilized cells and removal of the soluble cell fraction. This suggests that a soluble factor is involved in an autonomous process that inactivates guanylate cyclase and is triggered only after the enzyme is activated. The initial rate of guanylate cyclase activity in permeabilized cells is similar to that in intact, chemotactically activated cells. Moreover, the rate of inactivation of the enzyme in permeabilized cells and that due to adaptation in vivo are about equal. This suggests that the activation and inactivation of guanylate cyclase observed in this permeabilized cell system is related to that of chemotactic activation and adaptation in intact cells. © 1996 Wiley-Liss, Inc.
    Additional Material: 7 Ill.
    Type of Medium: Electronic Resource
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