Electrochemical and enzymatic oxidation of catecholamines involved in sclerotization and melanization of insect cuticle

Abstract

The electrochemical properties of catecholamines that occur in the haemolymph and cuticle of Manduca sexta (L.) during development were studied. The cyclic voltammetric behaviour for dopamine, N- acetyldopamine (NADA) and N-β-alanyldopamine (NBAD) was similar except that the open chain o- quinones of the latter two compounds cyclized significantly more slowly than dopamine o- quinone . Tyrosinase from pharate pupal cuticle oxidized the three catecholamines with NBAD and NADA being the preferred substrates. Oxidation to the corresponding o- quinone , indolization and reoxidation to p- quinone imine was the pathway observed for both electrochemical and enzyme catalyzed reactions. The possible roles of these metabolites in cuticle sclerotization and melanization are discussed.