Characterization and developmental regulation of tyramine-beta-hydroxylasein the CNS of the moth, Manduca sexta

Octopamine (OA) is present in insect nervous tissue, but little is known ab out its biosynthesis, In the CNS of Manduca sexta, OA levels increase marke dly during postembryonic adult development. To study this increase, we deve loped an assay for tyramine-beta-hydroxylase, the putatively rate-limiting enzyme for OA biosynthesis. Tyramine-beta-hydroxylase activity in extracts of M. sexta CNS tissue: (1) was time- and protein-dependent, and with prote in concentrations up to 2 mu g/mu l, was linear for 20 min; (2) had a pH op timum of 7.0 for conversion of tyramine to OA; (3) required ascorbate, copp er, and catalase; and (4) had an apparent K-M,K-tyramine of 0.22+/-0.04 mM. These characteristics resemble those of the mammalian enzyme dopamine-beta -hydroxylase, suggesting that these two enzymes are functionally related. D uring adult development, tyramine-beta-hydroxylase activity increased 11-fo ld in the brain and 9-fold in the abdominal ganglia, paralleling increases in OA levels in those CNS structures during metamorphosis. The apparent kin etic constants of tyramine-beta-hydroxylase suggested that the amount of th is enzyme present in the tissues increases. The increase in OA levels durin g adult development thus appears to be due to an increase in the level of e nzyme available for OA synthesis and may reflect an increase in the number of octopaminergic neurons. (C) 2000 Published by Elsevier Science Ltd. All rights reserved.