Ligand stabilization of cholinesterases.

Stabilization of fetal bovine serum (FBS) acetylcholinesterase (acetylcholine acetylhydrolase, EC 3.1.1.7) (AChE) and human butyrylcholinesterase (acylcholine acylhydrolase, EC 3.1.1.8) (BuChE) by ligands and inhibitors was studied as a function of physical and chemical perturbation. Denaturation of AChE occurred as a binary exponential function in the temperature range studied (50-56 degrees C); the slower fraction progressively diminished as the temperature was increased. Inclusion of ligands or inhibitors stabilized AChE as a function of temperature, ligand concentration and time. The rank order in which ligands stabilized AChE was: edrophonium greater than decamethonium greater than pralidoxime chloride much greater than procainamide. BuChE denaturation was retarded by ligands in the order: decamethonium greater than procainamide greater than edrophonium greater than pralidoxime. A plot of the quotient of the fast/slow ratio against the log of the 50% inhibitory concentration (I50) for ligands providing substantial protection yielded a linear relation, suggesting that these compounds stabilized AChE by a common mechanism involving the anionic site of the active center. Urea-induced cholinesterase denaturation was also retarded by these ligands.