Enzymatic N-Acetylation of Indolealkylamines by Brain Homogenates of the Honeybee, Apis Mellifera

Abstract

Brain homogenates of the honeybee, Apis mellifera, have been found to possess enzymes capable of catalyzing the N-acetylation of tryptamine and 5-hydroxytryptamine with acetyl coenzyme A as the acetyl donor. The Km of the N-acetylation of tryptamine was 5. 0 x 10-7 M at iii pH 7. 0 and 33°C. Evidence was obtained that the indolealkylamines, tryptamine and 5-hydroxytryptamine, are not oxidized by monoamine oxidase (MAO) as is commonly considered to be a major catabolic route in vertebrate animals. Certain commonly used assays, reportedly specific for monoamine oxidase activity, will not distinguish between oxidation by MAO and N-acetylation of tryptamine and so should not be used to assay for MAO activity in insect tissues without careful identification of the products of the reaction. Implications of N-acetylation of indolealkylamines are discussed in relation to the neurotransmitter problem.