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  • 1
    Electronic Resource
    Electronic Resource
    The origin of kinetic cooperativity in prehiotic catalysts (1996)
    Springer
    Journal of molecular evolution 43 (1996), S. 315-325 
    Details
    ISSN: 1432-1432
    Keywords: Primordial catalysts ; Template-like catalysts ; Kinetic cooperativity ; Ribozymes ; N 6-substituted adenine derivative
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Abstract A polyallylamine carrying long hydrophobic dodecyl groups and adenine residues as side chains (PALAD C12) may be able to catalyze the hydrolysis ofN-carbobenzoxy-l-alaninep-nitrophenyl ester (N-Cbz-Ala) as well asp-nitrophenyl acetate (pNPA). The progress curve of hydrolysis of the former displays a long lag and apparently no steady state. After this transient the rate falls off due to the accumulation of the products. Conversely, the hydrolysis ofp-nitrophenyl acetate displays classical burst kinetics followed by a slow decline of the reaction rate. Theoretical considerations show that a steady state may be expected to occur only if the concentration of the free catalyst is very small during the reaction. This condition is sufficient to allow the rate of disappearance of the substrate to be equal to the rate of appearance of the products, which is precisely a condition for the existence of a steady state. If the catalyst is poorly active and has a loose affinity for its substrate and product, the measurement of a significant reaction rate will require a much larger concentration of the catalyst. Therefore, under these conditions, one cannot expect a steady state to occur. The mathematical expression of the error made in the steady-state assumption has been derived. This error increases with the catalyst concentration and decreases if the affinity of the substrate for the catalyst is high. Therefore the lack of steady state is associated with the affinity (or the dissociation) of the substrate and the product for the catalyst. When this affinity is low, the free concentration of the catalyst during the reaction is high and one cannot expect a steady state to occur. This is precisely what takes place with N-Cbz-Ala. A mathematical expression of the rate of hydrolysis of N-Cbz-Ala and of any reactant that displays this type of kinetics may be derived at the end of the transient when the rate is close to its maximum value. Under these conditions the rate cannot follow classical Michaelis-Menten kinetics and displays positive cooperativity. It may therefore be speculated that primordial template-like catalysts that were displaying a poor affinity for their substrates and products were already exhibiting apparent positive cooperativity in the kinetic reactions they were able to catalyze.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF02339006
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    Paper (German National Licenses)
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  • 2
    Electronic Resource
    Electronic Resource
    The Origin of Kinetic Cooperativity in Prebiotic Catalysts (1996)
    Springer
    Journal of molecular evolution 43 (1996), S. 315-325 
    Details
    ISSN: 1432-1432
    Keywords: Key words: Primordial catalysts — Template-like catalysts — Kinetic cooperativity — Ribozymes —N6-substituted adenine derivative
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Abstract. A polyallylamine carrying long hydrophobic dodecyl groups and adenine residues as side chains (PALAD C12) may be able to catalyze the hydrolysis of N-carbobenzoxy-l-alanine p-nitrophenyl ester (N-Cbz-Ala) as well as p-nitrophenyl acetate (pNPA). The progress curve of hydrolysis of the former displays a long lag and apparently no steady state. After this transient the rate falls off due to the accumulation of the products. Conversely, the hydrolysis of p-nitrophenyl acetate displays classical burst kinetics followed by a slow decline of the reaction rate. Theoretical considerations show that a steady state may be expected to occur only if the concentration of the free catalyst is very small during the reaction. This condition is sufficient to allow the rate of disappearance of the substrate to be equal to the rate of appearance of the products, which is precisely a condition for the existence of a steady state. If the catalyst is poorly active and has a loose affinity for its substrate and product, the measurement of a significant reaction rate will require a much larger concentration of the catalyst. Therefore, under these conditions, one cannot expect a steady state to occur. The mathematical expression of the error made in the steady-state assumption has been derived. This error increases with the catalyst concentration and decreases if the affinity of the substrate for the catalyst is high. Therefore the lack of steady state is associated with the affinity (or the dissociation) of the substrate and the product for the catalyst. When this affinity is low, the free concentration of the catalyst during the reaction is high and one cannot expect a steady state to occur. This is precisely what takes place with N-Cbz-Ala. A mathematical expression of the rate of hydrolysis of N-Cbz-Ala and of any reactant that displays this type of kinetics may be derived at the end of the transient when the rate is close to its maximum value. Under these conditions the rate cannot follow classical Michaelis-Menten kinetics and displays positive cooperativity. It may therefore be speculated that primordial template-like catalysts that were displaying a poor affinity for their substrates and products were already exhibiting apparent positive cooperativity in the kinetic reactions they were able to catalyze.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/PL00006091
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    Paper (German National Licenses)
    Fulltext
  • 3
    Electronic Resource
    Electronic Resource
    Purification and molecular properties of acid phosphatase from sycamore cell walls (1980)
    Oxford, UK : Blackwell Publishing Ltd
    Plant, cell & environment 3 (1980), S. 0 
    Details
    ISSN: 1365-3040
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Biology
    Notes: Abstract. An acid phosphatase is isolated and purified to homogeneity from sycamore cell walls. The enzyme, which has a molecular weight close to 100,000, is a glycoprotein and is most probably made up of one polypeptide chain only. Its amino acid composition has been determined. Although homogeneous to polyacrylamide gel electrophoresis under non-denaturing conditions, the enzyme preparation still contains protease traces that tend to split polypeptide chain in two fragments.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1111/1365-3040.ep11581714
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    Paper (German National Licenses)
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  • 4
    Electronic Resource
    Electronic Resource
    Ionic control of acid phosphatase activity in plant cell walls (1980)
    Oxford, UK : Blackwell Publishing Ltd
    Plant, cell & environment 3 (1980), S. 0 
    Details
    ISSN: 1365-3040
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Biology
    Notes: Abstract. Purified acid phosphatase from sycamore cell walls is not activated by increasing the ionic strength of the reaction mixture. However activation occurs when the enzyme is bound to small cell wall fragments. The apparent activation of the bound enzyme by ions is paralleled by a decline of the substrate concentration C1/2, that results in half of the maximum rate. Above ionic strengths of about 0.05 the bound and solubilized enzyme forms behave in the same manner. Titration of cell wall fragments at different ionic strengths show that the local pH, inside the cell wall fragments, is lower than the pH in bulk solution. These results are explained in the light of poly-electrolyte theory. The negative charges of the cell walls generate an electrostatic potential that results in the attraction or repulsion of ions. The local concentration of organic phosphate (the substrate of the enzyme) is then lower than its concentration in bulk solution. This concentration difference explains that the value of C1/2, or of the apparent Km of the bound enzyme, is greater than the true Km of the solubilized enzyme. Increasing the ionic strength tends to equalize bulk and local ion concentrations, and therefore apparently activates the bound enzyme.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1111/1365-3040.ep11581782
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    Paper (German National Licenses)
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  • 5
    Electronic Resource
    Electronic Resource
    The ethics of biofungicides – A case study: Trichoderma harzianum ATCC 20476 on Elsanta strawberries against Botrytis cinerea (gray mold) (1997)
    Springer
    Agriculture and human values 14 (1997), S. 251-258 
    Details
    ISSN: 1572-8366
    Keywords: Biological control ; Biofungicides ; Ethical issues ; Food industry
    Source: Springer Online Journal Archives 1860-2000
    Topics: Agriculture, Forestry, Horticulture, Fishery, Domestic Science, Nutrition
    Notes: Abstract Trichoderma ATCC 20476 based biofungicides have been marketed continuously on a small scale for 20 years. A more recently developed application for these biofungicides is the treatment of strawberries against the gray mold Botrytis cinerea. That application is examined in terms of Lockwood's criteria for ethics in biological control. Unaddressed risks resulting from the current scramble for market share in northern Europe are pointed out.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1023/A:1007460813543
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    Paper (German National Licenses)
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  • 6
    Electronic Resource
    Electronic Resource
    Dynamics of enzyme reactions in solution and in heterogeneous media (1984)
    New York, NY : Wiley-Blackwell
    International Journal of Quantum Chemistry 26 (1984), S. 943-953 
    Details
    ISSN: 0020-7608
    Keywords: Computational Chemistry and Molecular Modeling ; Atomic, Molecular and Optical Physics
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Enzymes are catalysts occurring in living cells. The aim of this paper is to describe some basic properties of enzymes and to understand on a physical basis how the intracellular milieu may control the kinetics of enzyme reactions. We shall therefore consider in succession some kinetic properties of enzymes in solution and the way cell surfaces and biological membranes control the dynamics of enzyme reactions. The choice of topics which have been selected in this paper is somewhat arbitrary and certainly reflects the tastes and the personal interests of the authors.
    Additional Material: 8 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/qua.560260529
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    Paper (German National Licenses)
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