The sclerotization process by the american cockroach: Contribution of melanin

Abstract

Identical experiments using [2- 14C]dopa and [2- 14C]dopachrome (2-carboxy-5-oxo-6-oxo-indole) show that there is a tenfold increase in the incorporation of dopa into the cuticle after 8 hours. In vitro studies on the synthesis of melanin and the fact that dopachrome is translocated into the cuticle 6–8 hours after ecdysis suggest that indole melanin is at best only a secondary sclerotization agent. Tyrosine and tyramine are converted to melanin at a slow rate while dopa and dopamine conversion is three times as fast. Dopamine is the best substrate. The tanning hormone inhibits the formation of melanin presumably by forcing the dopa towards the synthesis of N-acetyl dopamine. Both the haemolymph and integument are capable of catalysing the reactions involved in the metabolism of dopa to melanin, but a synergistic effect is realized if the two are combined.