Coupling reactions between amino compounds and N-acetyldopamine catalyzed by cuticular enzymes

Abstract

Incubation of larval cuticle from the American silkmoth, Hyalophora cecropia with N-acetyldopamine (NADA) and amino acid derivatives results in a number of products. Some of the products obtained with α- N-acetyllysine and with β-alanine have been purified and identified. Two types of adducts are formed from both amino acids: one in which the amino group is linked to the 1-carbon atom (β-carbon) in the aliphatic side chain in NADA, and one in which the amino group is linked to the 6-position of the aromatic ring, followed by oxidation to a quinoid structure. Both types of NADA-adducts have also been obtained in experiments where adult pharate locust femur cuticle was incubated with NADA and either N-acetyllysine or β-alanine, demonstrating that products similar to those obtained by means of soft larval cuticle may also be formed in vitro by sclerotizing cuticle. Together with previous observations on cuticle-catalysed adduct formation between N-acetylhistidine and NADA the results indicate that amino groups as well as histidine residues in cuticular proteins can take part in the sclerotization process. The adducts involving the side chain of NADA have an intact o-diphenolic structure and are potential participants in formation of benzodioxan-type (also called dihydrobenzodioxin-type) NADA-oligomers. Co-incubation of NADA with the β-alanyl NADA adduct and locust cuticle gave products containing both the benzodioxan-structure and covalently attached β-alanine, indicating that NADA linked to cuticular amino groups may participate in polymerization reactions during natural sclerotization.