Chemical modification of acetylcholinesterase from eel and basal ganglia: effect on the acetylcholinesterase and aryl acylamidase activities

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Abstract
The effect of chemical modification on the acetylcholinesterase (AChE) and the aryl acylamidase (AAA) activities of purified AChE from electric eel and sheep basal ganglia was investigated in the presence and absence of acetylcholine, the substrate of AChE, and 1,5-bis[4-(allyldimethylammonium)phenyl]pentan-3-one dibromide (BW284C51), a reversible competitive inhibitor of AChE. Trinitrobenzenesulfonic acid, pyridoxal phosphate, acetic anhydride, diethyl pyrocarbonate and 2-hydroxy-5-nitrobenzyl bromide under specified conditions inactivated both AChE and AAA in the absence of acetylcholine and BW284C51. Chemical modifications in the presnece of acetylcholine and BW284C51 by all of the above except diethyl pyrocarbonate selectively prevented the loss of AChE but not AAA activity; modification by diethyl pyrocarbonate in the presence of acetylcholine and BW284C51 prevented the loss of both AChE and AAA activities. Treatment with N-acetylimidazole resulted in the inactivation of AChE and the activation of AAA. These changes in both the activities could be prevented by acetylcholine and BW284C51. Modification by phenylglyoxal, 2,4-pentanedione or N-ethylmaleimide did not affect the enzyme activities. Indophenylacetate hydrolase activity followed a pattern similar to that of AChE in all the above modification studies. The results suggested essential lysine, tyrosine, tryptophan and histidine residues for the active center of AChE and essential lysine, histidine and tryptophan residues for the active center of AAA. On the basis of the acetylcholine and BW284C51 protection studies, the active centers appeared to be situated at different loci with histidine and tyrosine as common residues.