Acceleration of Drosophila melanogaster acetylcholinesterase methanesulfonylation: peripheral ligand D-tubocurarine enhances the affinity for small methanesulfonylfluoride.
D-Tubocurarine, a reversible peripheral inhibitor of cholinesterases accelerates methanesulfonylation of Drosophila melanogaster wild type and W359L mutant. The kinetic evaluation of the process was performed in a step-by-step analysis. The second order overall sulfonylation rate constants, determined from classical residual activity measurements, were used in the subsequent analysis of progress curves. The latter were obtained by measuring the hydrolysis of acetylthiocholine in a complex reaction system of enzyme, substrate, irreversible and reversible inhibitor. The underlying kinetic mechanisms, from such a complex data, could only be untangled by targeted inspection and successive incorporation of reaction steps for which experimental evidence existed. The study showed that the peripheral ligand D-tubocurarine, by binding at the entrance into the active site of the two investigated enzymes (Golicnik et al., Biochemistry 40 (2001) 1214), enhances the affinity for small methanesulfonylfluoride, rather to speeding up the formation of a stable covalent enzyme-inhibitor complex. The specific arrangements at the rim of the active site of each individual enzyme dictate the actual events which can be detected by kinetic means.
Golicnik
Marko
M
Institute of Biochemistry, Medical Faculty, University of Ljubljana, Vrazov trg 2, 1000 Ljubljana, Slovenia.
Fournier
Didier
D
Stojan
Jure
J
D000110:Acetylcholinesterase / Q000235:genetics / Q000378:metabolism*; D000122:Acetylthiocholine / Q000378:metabolism; D000818:Animals; D001665:Binding Sites / Q000187:drug effects; D002800:Cholinesterase Inhibitors / Q000378:metabolism*; D004305:Dose-Response Relationship, Drug; D004331:Drosophila melanogaster / Q000201:enzymology* / Q000235:genetics; D004789:Enzyme Activation; D007700:Kinetics; D008024:Ligands; D013450:Sulfones / Q000378:metabolism*; D014403:Tubocurarine / Q000494:pharmacology*
D002800:Cholinesterase Inhibitors; D008024:Ligands; D013450:Sulfones; D000122:Acetylthiocholine; C005109:methanesulfonyl fluoride; D000110:Acetylcholinesterase; D014403:Tubocurarine