Inhibition of acetylcholine esterase and butyrylcholine esterase with isoquinoline alkaloids

Abstract

The inhibition of the mentioned enzymes with 16 natural and modified isoquinoline alkaloids was investigated. Protoberberines are very strong inhibitors of both enzymes, quaternary tetrahydroprotoberberines and benzylisoquinolines are comparably strong in butyrylcholine esterase and slightly weaker in the case of acetylcholine esterase. Representatives of the pavinane and protopine groups are the weakest inhibitors of both enzymes in the series tested. The results confirm that these substances are bound competitively to butyrylcholine esterase and non-competitively to acetylcholine esterase, and they also show that the charge has a decisive effect on the force of the interaction. On the other hand the effect of the hydrophobicity of the inhibitor molecule on the bond strength is relatively small. Among the substances tested allylberberrubine is the strongest inhibitor of butyrylcholine esterase, its inhibition constant is 1.3 . 10-7.