Effects of potential inhibitors on N‐acetylation of octopamine by tissue extracts from malpighian tubules and cerebral ganglia of Periplaneta americana L

Abstract

N-acetyltransferase activity in extracts of Malpighian tubules and cerebral ganglia from Periplaneta americana L. was monitored using high performance liquid chromatography with coulometric electrochemical detection. Several potential inhibitors were tested against the tissue preparations, and the results indicate distinct differences in the nature of the enzyme derived from the two sources. The Malpighian tubule and cerebral ganglia extracts were sensitive to sulfhydryl inhibition and divalent cations, and both preparations also showed end-product inhibition with coenzyme A. Juglone, an inhibitor of choline acetyltransferase, inhibits N-acetyltransferase activity from both tissues; however, separate studies with choline indicate that the N-acetylation observed in this study is not due to choline acetyltransferase. A number of phenyl, phenol, catechol and indole derivatives were tested and the results indicate that the presence of a 4-hydroxyl group on the phenol ring enhances the capacity of phenol and catechol derivatives to inhibit N-acetyltransferase. Demethylchlordimeform inhibits the production of N-acetyl-p-Octopamine by Malpighian tubule preparations and intact tissues whereas other formamidines, BTS-27271 and amitraz, inhibit N-acetyl-p-Octopamine production only in intact tissues.