ABSTRACT
This chapter examines in vitro studies of the hormonal regulation of cuticular melanization and associated enzymes, phenoloxidase (PO) and dopa decarboxylase (DDC). Both PO and DDC are key enzymes in the melanization process in Manduca sexta cuticle. Normally, Manduca larvae have a transparent cuticle. DDC activity was found primarily in the epidermis with small amounts in the cuticle and the fat body and none in the hemolymph. By the onset of melanization, dopamine was accumulating in the epidermis; then as melanization proceeded, dopamine was incorporated into the cuticle. The PO in the premelanin granules is a diphenoloxidase and was found to be separable by electrophoresis from both the wound PO found in the old cuticle and the hemolymph PO, so it was isolated and an antibody prepared. During synthesis and deposition the PO is inactive. Once activated, this PO can oxidize the dopamine — synthesized by the epidermis and transported to the granules — to melanin within the granules.
