Author/Editor		Stojan, Jure; Goličnik, Marko; Froment, Marie-Therese; Estour, Francois; Masson, Patrick
Title		Concentration-dependent reversible activation-inhibition of human butyrylcholinesterase by tetraethylammonium ion
Type		članek
Source		Eur J Biochem
Vol. and No.		Letnik 269, št. 4
Publication year		2002
Volume		str. 1154-61
Language		eng
Abstract		Tetraalkylammonium (TAA) salts are well known reversible inhibitors of cholinesterases. However, at concentrations around 10 mm, they have been found to activate the hydrolysis of positively charged substrates, catalyzed by wild-type human butyrylcholinesterase (EC 3.1.1.8) ŠErdoes, E.G., Foldes, F.F., Zsigmond, E.K., Baart, N. & Zwartz, J.A. (1958) Science 128, 92Ć. The present study was undertaken to determine whether the peripheral anionic site (PAS) of human BuChE (Y332, D70) and/or the catalytic substrate binding site (CS) (W82, A328) are involved in this phenomenon. For this purpose, the kinetics of butyrylthiocholine (BTC) hydrolysis by wild-type human BuChE, by selected mutants and by horse BuChE was carried out at 25 degreeC and pH 7.0 in the presence of tetraethylammonium (TEA). It appears that human enzymes with more intact structure of the PAS show more prominent activation phenomenon. The following explanation has been put forward: TEA competes with the substrate at the peripheral site thus inhibiting the substrate hydrolysis at the CS. As the inhibition by TEA is less effective than the substrate inhibition itself, it mimics activation. At the concentrations around 40 mm, well within the range of TEA competition at both substrate binding sites, it lowers the activity of all tested enzymes.
Descriptors		BUTYRYLCHOLINESTERASE HYDROLYSIS BUTYRYLTHIOCHOLINE TETRAETHYLAMMONIUM COMPOUNDS KINETICS BINDING SITES MODELS, CHEMICAL