tailieunhanh - Báo cáo Y học: Concentration-dependent reversible activation-inhibition of human butyrylcholinesterase by tetraethylammonium ion

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 ) [Erdoes, ., Foldes, ., Zsigmond, ., Baart, N. & Zwartz, . (1958) Science 128, 92]. | Eur. J. Biochem. 269 1154-1161 2002 FEBS 2002 Concentration-dependent reversible activation-inhibition of human butyrylcholinesterase by tetraethylammonium ion Jure Stojan1 Marko Golicnik1 Marie-Therese Froment2 Francois Estour2 and Patrick Masson2 1 Institute of Biochemistry Medical Faculty University of Ljubljana Slovenia 2 Centre de Recherches du Service de Sante des Armees Unite d Enzymologie La Tronche France 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 Erdoes . Foldes . Zsigmond . Baart N. Zwartz . 1958 Science 128 92 . 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 C and pH 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. Keywords cholinesterases tetraalkylammonium compounds kinetics reaction mechanism. Acetylcholinesterase AChE EC and butyrylcholinesterase BuChE EC are closely related serine hydrolases 1 . No clear physiological function has yet been assigned to BuChE it appears to play a role in .