1,2-dehydro-N-beta-alanyldopamine as a new intermediate in insect cuticular sclerotization.

Sclerotization of insect cuticle is an extremely important biochemical process for the successful survival of most insects. N-Acetyldopamine and N-beta-alanyldopamine are two widely used sclerotizing precursors. N-Acetyldopamine is converted by phenoloxidase, quinone isomerase, and quinone methide isomerase to generate the reactive intermediates quinone, quinone methide, and quinone methide imine amide for use in quinone tanning, quinone methide sclerotization, and alpha,beta-sclerotization, respectively. N-beta-Alanyldopamine has been claimed to be used only by phenoloxidase and quinone isomerase for quinone tanning and quinone methide sclerotization thereby attributing biochemical diversity to the coloration and strength of different cuticles. However, we demonstrate here that cuticular enzymes isolated from the larvae of Calliphora possess the capacity to generate 1,2-dehydro-N-beta-alanyldopamine from N-beta-alanyldopamine. Chemical synthesis of 1,2-dehydro-N-beta-alanyldopamine and its further oxidation are reported for the first time. Comparative biochemical studies confirm that both the sclerotizing precursors, N-acetyldopamine and N-beta-alanyldopamine, are used by all three different mechanisms of the unified theory of sclerotization.