Effect of choline esters on the decarbamylation of dimethylcarbamyl-acetylcholinesterase.

Acetylcholine and butyrylcholine exhibited the dose-dependent decarbamylation up to 0.2 mM, although at higher concentrations the decarbamylation degree declined. In combination with choline, butyrylcholine potentiated the choline-catalyzed decarbamylation by 30-100%, and was found to be more effective than acetylcholine in enhancing the decarbamylation. In kinetic analysis, it was observed that Ka value of choline was not remarkably altered by butyrylcholine whereas the maximum rate for decarbamylation was enhanced significantly in the presence of butyrylcholine, suggesting that butyrylcholine may affect the decarbamylation by interacting with the peripheral sites, different from the central active site which choline is known to interact with. In support of the suggestion, butyrylcholine was observed to compete with gallamine, a well known peripheral activator, and the effect of butyrylcholine was enhanced by three times at low ionic strength. In addition, acetylcholinesterase from mouse brain or bovine erythrocyte seemed to differ from electric eel enzyme in the interaction with butyrylcholine.