Octapamine N-acetyltransferase activity from the cattle tick, Boophilus microplus

Abstract

The metabolism of octopamine in the tick, Boophilus microplus, was studied by incubating synganglia, excised from adult females, with [ 3H]octopamine. The major metabolite co-chromatographed with N-acetyloctopamine and was predominantly found outside the nervous tissue in the surrounding saline. The N-acetyltransferase (NAT) activity was measured in enzyme preparations from adult synganglia using [ 3H]octopamine as the substrate and acetyl CoA as a co-factor. Under the assay conditions employed, the V max was 7 nmol/h/mg of protein and the apparent K m for octopamine was 4 μM. The N-acetylation of octopamine was inhibited by divalent cations (Zn 2+ and Cu 2+), β-carbolines, imipramine and a number of biogenic amines. NAT activity towards octopamine was also found in enzyme preparations from larvae of B. microplus and this enzyme had similar K m and V max values (4 μM and 10 nmol/h/mg of protein, respectively) to the neural enzyme and was inhibited both by β-carbolines and biogenic amines. These results suggest that N-acetylation is a key reaction in the metabolism of octopamine in the nervous system of the tick and may also play an important role in the metabolism of octopamine and other biogenic amines in larval stages of this acarine.