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  • 1
    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
  • 2
    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
    Library Location Call Number Volume/Issue/Year Availability
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    Paper (German National Licenses)
    Fulltext
  • 3
    Electronic Resource
    Electronic Resource
    Studies in primitive catalysis and nucleoside analogs (1996)
    Springer
    Origins of life and evolution of the biospheres 26 (1996), S. 244-245 
    Details
    ISSN: 1573-0875
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Geosciences
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF02459736
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    Paper (German National Licenses)
    Fulltext
  • 4
    Electronic Resource
    Electronic Resource
    Synthesis and catalytic activity of adenine containing polyamines (1995)
    Weinheim : Wiley-Blackwell
    Macromolecular Chemistry and Physics 196 (1995), S. 2615-2624 
    Details
    ISSN: 1022-1352
    Keywords: Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Physics
    Notes: N6-Ribosyladenine has been obtained as a major product in the condensation of adenine and ribose under presumably prebiotic conditions. This abnormal nucleoside exhibits a pronounced catalytic activity as compared to histidine, in the hydrolysis of p-nitrophenyl acetate. The N6-substituted adenine ring could be considered as a substitute for the imidazole moiety, which could have played a catalytic role in primitive enzymes. To study in more details the catalytic properties of such a group when placed in a favourable microenvironment, it was linked to poly(allylamine). The presence of one adenine ring in ten residues accelerated the p-nitrophenyl butyrate hydrolysis at pH 8. The rate was increased two-fold compared to the starting polymer and 100-fold compared to free adenine. A remarkable, more than 400-fold acceleration compared to free adenine was measured when long hydrophobic dodecyl side chains were attached as substrate binding sites on the polyamine containing adenine rings. Under mild basic conditions, the catalytic activity of the polymers in the hydrolysis of p-nitrophenyl esters strongly increases with pH. A cooperative effect between the unprotonated aliphatic amino groups and adenine rings in proton transfers could explain these results. The imidazole ring of N6-substituted adenine derivatives could act in catalysis with water as a proton-relay system through a tautomeric equilibrium as the imidazole residue in actual enzymes.
    Additional Material: 5 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/macp.1995.021960814
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    Paper (German National Licenses)
    Fulltext
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