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Home / Equine Research Bank / Biochem J / A steady-state kinetic model of butyrylcholinesterase from h...
The Biochemical journal1974; 141(3); 825-834; doi: 10.1042/bj1410825

A steady-state kinetic model of butyrylcholinesterase from horse plasma.

Abstract: The steady-state kinetics of the butyrylcholinesterase-catalysed hydrolysis of butyrylthiocholine and thiophenyl acetate were shown to deviate from Michaelis-Menten kinetics. The ;best' empirical rate law was selected by fitting different rate equations to the experimental data by non-linear regression methods. The results were analysed in view of two alternative interpretations: (1) the reaction is catalysed by a mixture of enzymes, or (2) the activity is due to a single enzyme displaying deviations from Michaelis-Menten kinetics. It was concluded that the second alternative applies, and this conclusion was further supported by experiments involving simultaneous hydrolysis of alternative thiol ester substrates (butyrylthiocholine/thiophenyl acetate) as well as alternative thiol ester and oxygen ester substrates (butyrylthiocholine/phenyl acetate; thiophenyl acetate/butyrylcholine; acetylthiocholine/phenyl acetate). On the basis of the conclusion that a single enzyme is responsible for the activity, a molecular model is proposed. This model involves an acylated enzyme, and implies binding to the enzyme of one acyl group and one ester molecule, but not two ester molecules at the same time. Thus butyrylcholinesterase, which is structurally a tetramer, behaves functionally as a co-operative dimer, an interpretation in accordance with available data from active-site titrations.
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Publication Date: 1974-09-01 PubMed ID: 4463963PubMed Central: PMC1168188DOI: 10.1042/bj1410825Google Scholar: Lookup
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  • Journal Article

Summary

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The research explores the enzymatic behavior of butyrylcholinesterase from horse plasma, concluding that it behaves as a cooperative dimer despite its structural tetramer composition and proposing a molecular model.

Steady-State Kinetics and Deviation from Michaelis-Menten Model

  • The study focused on the steady-state kinetics of butyrylcholinesterase – a type of enzyme that assists in chemical reactions, from horse plasma.
  • It was discovered that the hydrolysis (a chemical reaction involving the breakdown of a compound due to its interaction with water molecules) of butyrylthiocholine and thiophenyl acetate deviated from the expected Michaelis-Menten kinetics.
  • The Michaelis-Menten model is traditionally used in enzyme kinetics that describes the rate of enzymatic reactions by relating kinetic data to reaction rates, which here was found not applicable.

Selecting the ‘Best’ Empirical Rate Law

  • Different rate equations were fitted to the experimental data in order to find the ‘best’ empirical rate law.
  • This fitting was done using non-linear regression methods, a statistical technique that helps to model the relationship between the two variables.

Analysis of Results and Interpretations

  • The researchers analysed their results by considering two alternative interpretations: either the reaction is catalysed by a mixture of enzymes or the activity is due to a single enzyme displaying deviations from Michaelis-Menten kinetics.
  • They concluded that the second interpretation was the most likely, based on their experiment’s results.
  • To further validate this conclusion, more experiments were conducted. These experiments involved the simultaneous hydrolysis of alternative thiol ester substrates such as butyrylthiocholine, thiophenyl acetate, among others.

Proposed Molecular Model

  • The researchers then proposed a molecular model based on their conclusion that only a single enzyme is responsible for the activity noted.
  • This model involved the concept of an “acylated” enzyme, which refers to an enzyme that has been converted to accept an acyl group (a type of chemical group derived from carboxylic acids).
  • According to their model, this enzyme is capable of binding to one acyl group and one ester molecule, but not two ester molecules at the same time.
  • The research further revealed that the butyrylcholinesterase enzyme behaves functionally as a cooperative dimer (a complex formed by two molecules), a conclusion that is consistent with existing data from active-site titrations despite its structural tetramer form.

Cite This Article

APA
Augustinsson KB, Bartfai T, Mannervik B. (1974). A steady-state kinetic model of butyrylcholinesterase from horse plasma. Biochem J, 141(3), 825-834. https://doi.org/10.1042/bj1410825

Publication

The Biochemical journal
ISSN: 0264-6021
NlmUniqueID: 2984726R
Country: England
Language: English
Volume: 141
Issue: 3
Pages: 825-834

Researcher Affiliations

Augustinsson, K B
    Bartfai, T
      Mannervik, B

        MeSH Terms

        • Animals
        • Binding Sites
        • Butyrates
        • Catalysis
        • Cholinesterases / blood
        • Esters
        • Horses
        • Hydrolysis
        • Kinetics
        • Models, Chemical
        • Sulfhydryl Compounds

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        Citations

        This article has been cited 2 times.
        1. Kris M, Jbilo O, Bartels CF, Masson P, Rhode S, Lockridge O. Endogenous butyrylcholinesterase in SV40 transformed cell lines: COS-1, COS-7, MRC-5 SV40, and WI-38 VA13. In Vitro Cell Dev Biol Anim 1994 Oct;30A(10):680-9.
          doi: 10.1007/BF02631271pubmed: 7842168google scholar: lookup
        2. Lindgren C, Rajeshwari R, Engdahl CS, Kumari R, Ekström F, Linusson A. The Molecular Properties of Honey Bee Acetylcholinesterase Reveal Opportunities to Avoid Off-Target Effects in Insecticide Discovery. Chemistry 2025 Jul 8;31(38):e202500664.
          doi: 10.1002/chem.202500664pubmed: 40501143google scholar: lookup
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