DOPA and tyrosine decarboxylation in the cockroach Leucophaea maderae in relation to cuticle formation and ecdysis

Abstract

Patterns of tyrosine metabolism were studied throughout cuticle formation, ecdysis, and sclerotization in larval and adult cockroaches, Leucophaea maderae. Decarboxylation in vivo of tyrosine was very low in last instars and pharate adults. DOPA decarboxylase activity in haemolymph and certain tissues was also low but increased rapidly at ecdysis. Extensive conversion of tyrosine to two-carbon side-chain metabolites began near ecdysis and lasted for several days, as evidenced by high 1- 14CO 2 but almost no 14CO 2 from side-chain carbons 2 or 3. DOPA decarboxylase in the haemolymph and integument also reached highest activity during this interval, with the former about four times more active than the latter. In newly ecdysed larvae and adults, haemolymph DOPA decarboxylase was 30 times more active than tyrosine decarboxylase; the latter remained very low throughout the inter-ecdysial and ecdysial periods. After sclerotization, haemolymph and integument DOPA decarboxylase activity gradually declined to pre-ecdysial levels in both larvae and adults. Decarboxylation of tyrosine in vivo decreased for several days after ecdysis in adult insects and leveled off at an activity five times that of larvae. Production of 2- and 3- 14CO 2 increased with adult age indicating a shift in pathways to production of 1-carbon side-chain and simple ring metabolites.