Enzymatic activities involved in incorporation of N-acetyldopamine into insect cuticle during sclerotization

Abstract

During sclerotization of insect cuticle, N-acetyldopamine (NADA) is enzymatically oxidized before reaction with cuticular proteins. Not all oxidized NADA reacts with cuticular structural materials, a small fraction reacts with water or other available low molecular weight compounds to give soluble products. Various types of cuticle were incubated with excess NADA and the products studied by reversed phase high performance liquid chromatography (RP-HPLC) to obtain information on the enzymatic activities in the cuticle. The occurrence of at least two enzymes competing for NADA and present in different proportions in the various types of cuticle can explain the results. NADA may be incorporated into cuticle via α,β-dehydro-NADA (β-sclerotization) or via quinone methides and o-quinones, and the actual course of sclerotization will depend upon the relative activities of the enzymes involved. The various pathways may all be used simultaneously.