Biosynthesis of N-acetyldopamine and N-acetyloctopamine by Schistocerca gregaria nervous tissue

N-Acetyltyramine, N-acetyldopamine and N-acetyloctopamine were the major products when either L-[3H]tyrosine or [3H]tyramine were incubated with thoracic ganglia of the desert locust, Schistocerca gregaria. No label was incorporated into L-DOPA under these conditions, although 2-3% of the radioactivity could be recovered in dopamine and octopamine. Addition of the aromatic amino acid decarboxylase inhibitor, 3-hydroxybenzylhydrazine (NSD 1015), prevented the formation of N-acetylcompounds from L-[3H]tyrosine, without resulting in an accumulation of label in L-DOPA. In contrast, incubation of samples of haemolymph with L-[3H]tyrosine resulted in the recovery of 7% of label in L-DOPA, which was increased to 17% in the presence of NSD 1015. These results provide evidence that the initial step in the synthesis of dopamine and octopamine by S. gregaria nervous tissue is the conversion of L-tyrosine to tyramine, which is subsequently metabolised to N-acetyltyramine, N-acetyldopamine or N-acetyloctopamine.