Structure-Functional Effects of Ethanol on Drosophzla Melanogaster Acetylcholinesterase Probed by Kinetic Studies with Substrate and Inhibitors

Abstract

Ethanol is commonly used to extract and dissolve insecticides acting as inhibitors of acetyl-cholinesterase (EC 3.1.1.7). Here, experiments were undertaken to investigate the influence of solvent on the reaction and inhibition of the enzyme from Drosophila melanogaster. Ethanol (up to 20% by volume) is shown to induce a dramatic reduction of the affinity of acetylcholinester-ase for the acetylthiocholine iodide substrate and all the edrophonium chloride, paraoxon ethyl and propidium diiodide inhibitors, with little influence on the rate constants. Taken together, these results point to a main perturbation of active-center related components involved in the formation and/or stability of Michaelis complexes. Inactivation and ligand-stabilization studies of acetylcholinesterase activity further indicate the occurrence of specific ‘conformational scrambling” at catalytic and regulatory sites. It is proposed that ethanol affects the enzyme reactivity by modifying the conformation of the aromatic gorge containing the active centre and hence, interactions involved in the molecular recognition of substrates and ligands.

Key Words:

• Acetylcholinesterase
• Ethanol
• Acetylthiocholine iodide
• Paraoxon ethyl
• Edrophonium chloride
• Propidium diiodide
• Michaelis complexes