A putative kinetic model for substrate metabolisation by Drosophila acetylcholinesterase

FEBS Letters

Marcel, Véronique²  Fournier, Didier²  Estrada-Mondaca, Sandino²  Masson, Patrick¹  Stojan, Jure³  Klaebe, Alain² 

[1] Centre de Recherches du Service de Santé des Armées, Unité de Biochimie, 24 Avenue des Maquis du Grésivaudan, P.O. Box 87, 38702 La Tronche, Cedex, France;Laboratoire d'Entomologie et Groupe de Chimie Organique Biologique, Université Paul Sabatier, 31062 Toulouse, France;Institute of Biochemistry, Medical Faculty, Ljubljana, Slovenia

关键词: Acetylcholinesterase;    Substrate metabolization;    Drosophila;    AChE;    acetylcholinesterase;   

DOI  :  10.1016/S0014-5793(98)01434-3

学科分类：生物化学/生物物理

来源: John Wiley & Sons Ltd.

【 摘 要 】

Insect acetylcholinesterase, an enzyme whose catalytic site is located at the bottom of a gorge, can metabolise its substrate in a wide range of concentrations (from 1 μM to 200 mM) since it is activated at low substrate concentrations. It also presents inhibition at high substrate concentrations. Among the various rival kinetic models tested to analyse the kinetic behaviour of the enzyme, the simplest able to explain all the experimental data suggests that there are two sites for substrate molecules on the protein. Binding on the catalytic site located at the bottom of the gorge seems to be irreversible, suggesting that each molecule of substrate which enters the active site gorge is metabolised. Reversible binding at the peripheral site of the free enzyme has high affinity (2 μM), suggesting that this binding increases the probability of the substrate entering the active site gorge. Peripheral site occupation decreases the entrance rate constant of the second substrate molecule to the catalytic site and strongly affects the catalytic activity of the enzyme. On the other hand, catalytic site occupation lowers the affinity of the peripheral site for the substrate (34 mM). These effects between the two sites result both in apparent activation at low substrate concentration and in general inhibition at high substrate concentration.

【 授权许可】

Unknown