In vitro[formula omitted] of biogenic amines by tissues of the european corn borer, Ostrinia nubilalis Hübner

Abstract

[ 14 C]-N- Acetyltryptamine was the major product of tryptamine metabolism using whole larval European corn borer ( Ostrinia nubilalis) (Hübner) homogenates, as well as homogenates of corn borer brain, suboesophageal ganglion, nervecord, gut, Malpighian tubule, fat body and carcass, with either [ 14C]-tryptamine or [ 14C]-acetyl CoA as the labelled substrate. Indoleacetic acid and indoleacetaldehyde, the products of tryptamine metabolism by monoamine oxidase (MAO), were barely detectable, indicating that tryptamine metabolism in both neural and non-neural larval corn borer tissues is catalyzed predominantly by an arylamine acetyltransferase (AAT) rather than MAO. The highest specific activity of AAT was found in brain homogenates, although the highest activities per insect equivalent of tissue were found in carcass and fat body homogenates. The AAT activity in brain and carcass homogenates towards eight indolealkylamines and phenylethylamines showed clear differences in substrate specificity, particularly in the preference found in carcass but not brain homogenates for β-hydroxylated phenylethylamines over unsubstituted analogues. These results suggest that neural AAT may be a different enzyme than that found in non-neural tissues.