engleski

Competitive and noncompetitive inhibition of horse serum butyrylcholinesterase by ethopropazine

The inhibition of purified horse serum butyrylcholinesterase (BChE, EC 3.1.1.8) by racemic ethopropazine, 10-(2-diethylaminopropyl)phenothiazine hydrochloride (0.5-10 (M) was measured with acetylthiocholine (ATCh ; 0.1 - 50 mM) as substrate. For each substrate and inhibitor concentration, the apparent enzyme-inhibitor dissociation constant (Kapp) was calculated. The effect of substrate on Kapp was interpreted according to a model derived for equilibrium conditions with the following assumptions: the enzyme has a catalytic site and a non-productive, peripheral site, where both substrate or inhibitor can bind, and binding to the peripheral site can occur to both the free enzyme and to the enzyme-substrate Michaelis complex. In that model binding to the acylated enzyme is not taken into account. Between 0.10 and 1.0 mM ATCh, ethopropazine revealed non-competitive inhibition and the calculated enzyme-inhibitor dissociation constant was 0.86 (M. Competition between ATCh and ethopropazine was found between 1.0 and 50 mM ATCh ; over that concentration range the Kapp increased about 20-fold. The obtained enzyme-inhibitor dissociation constants will be compared with those obtained by applying a model for combined steady-state and equilibrium conditions, which allows binding of substrate or inhibitor to both the free and acylated BChE. In that model binding to the Michaelis complex is not taken into account. This work is a part of the Croatian-Slovenian joint project supported by the Ministries of Science and Technology of the Republic of Croatia and of Slovenia.

nije evidentirano

nije evidentirano