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A putative kinetic model for substrate metabolisation by Drosophila acetylcholinesterase
Author(s) -
Stojan Jure,
Marcel Véronique,
Estrada-Mondaca Sandino,
Klaebe Alain,
Masson Patrick,
Fournier Didier
Publication year - 1998
Publication title -
febs letters
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.593
H-Index - 257
eISSN - 1873-3468
pISSN - 0014-5793
DOI - 10.1016/s0014-5793(98)01434-3
Subject(s) - acetylcholinesterase , drosophila (subgenus) , substrate (aquarium) , chemistry , kinetic energy , stereochemistry , biochemistry , biology , enzyme , ecology , physics , gene , quantum mechanics
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.