Conference paper

The Reaction Mechanism of Butyrylcholinesterase

Klas-Bertil Augustinsson ; Department of Biochemistry, Arrhenius Laboratory, University of Stockholm, S-104 05 Stockholm, Sweden
Hakan Eriksson ; Department of Biochemistry, Arrhenius Laboratory, University of Stockholm, S-104 05 Stockholm, Sweden

Abstract

The kinetics of butyrylcholinesterase, present in human and
horse plasma, cannot be described by the Michae1is-Menten
equation, demonstrated with enzyme preparations of various
degrees of purity. This deviation from a simple kinetic model is
best described by a mathematical model for the rate equation
of a single enzyme with two catalytic sites. The structure of the
Hill plots is an additional indication that the substrate dnteractions
are of the homotropic co-operative type.
The effect of certain specific cholinesterase inhibitorn resulted
in linear Dixon plots with butyrylthiocholine as substrate and a
more complex effect with thiophenyl acetate or butyrate. Inhibitors
as choline might form dead-end complexes with free and monoacylated
enzyme. A mechanistic model with butyrylthiocholine as substrate is
proposed and can be extended to fit also with thiophenyl esters.
This model involves a co-operative pair of catalytic sites, but
no allosteric substrate binding site, and includes a mono- and
diacylated enzyme intermediate.

Keywords

Hrčak ID:

196591

URI

https://hrcak.srce.hr/196591

Publication date:

3.12.1975.

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