Conference paper

Kinetic Study of the Effect of Substrates on Reversible Inhibition of Cholinesterase and Acetylcholinesterase by Two Coumarin Derivatives

Elsa Reiner ; Biochemical Laboratory, Institute for Medical Research and Occupational Health, Yugoslav Academy of Sciences and Arts, Zagreb, Croatia, Yugoslavia
Vera Simeon ; Biochemical Laboratory, Institute for Medical Research and Occupational Health, Yugoslav Academy of Sciences and Arts, Zagreb, Croatia, Yugoslavia

Abstract

The reversible inhibition of cholinesterase and acetylcholinesterase
by coumarin and haloxon was studied in the presence
of phenylacetate and acetylthiocholine as substrates. The degree
of inhibition, expressed as v[I]/(v0
- v) , was shown to be linear
function of the substrate concentration. The linearity is maintained
for the inhibition by both inhibitors, and regardless of either the
kinetics of the enzyme-substrate reaction, or the enzyme inhibition
by the substrate itself. At given substrate concentrations the ratio
v[I]/(v0
- v) is constant, regardless of the inhibitor concentration.
The intercept on the ordinate of the line v[I]/(v0 - v) vs. [SJ,
represents the dissociation constant K(I) of the enzyme-inhibitor
complex. The intercept on the abscissa K(S) is characteristic of
the enzyme-substrate reaction ; the experimentally obtained values
were shown to be larger than the corresponding Michaelis constants.
Theoretical possibilities are discussed of the enzyme-
inhibitor and enzyme-substrate binding sites in order to interpret
the K(S) constants. Equations are derived for the binding of the
inhibLtor to the catalytic site (according to the Krupka and Laidler
theory) or an allosteric site on the enzyme (according to the
Aldridge and Reiner theory). Neither theoretical equation corresponds
to the experimentally obtained results. The kinetics of the
studied reactions is apparently more simple than theoretically
predicted.

Keywords

Hrčak ID:

196603

URI

https://hrcak.srce.hr/196603

Publication date:

3.12.1975.

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