La gestion des acides aminés aromatiques chez les Lépidoptères

Abstract

Lepidoptera, like other insects (sensu stricto, i.e., without their possible symbionts), require an exogenous input of aromatic nuclei. Phenylalanine must thus be considered as an essential amino acid; however, the most important aromatic metabolite is tyrosine. In addition to being incorporated into proteins, tyrosine goes through specific stages that are either transitory (storage or mobilization forms) or terminal in some of the major functional pathways in insects (generally through previous hydroxylation into catecholic substances). Some polypeptids incorporate tyrosyl residues either for structural or for metabolic storage purposes. Studies on insect neurochemistry have revealed the existence of neuroactive phenolamines and catecholamines. Although the chemistry of melanin formation is important in understanding certain physiological phenomena that affect both larval and adult Lepidoptera, it has never been studied in detail because of its complexity. Biochemical studies of sclerotization, which have been extensive during the past 20 years, have recently revealed several specific lepidopteran characteristics. Lepidoptera use a specific transitory storage form of tyrosine, β-D-glycopyranosyl-O-tyrosine, and the process of N-acylation, which affects dopamine at the time of nymphal ecdysis, leads to the formation of N-β-alanyldopamine instead of N-acetyldopamine as was shown by classic studies on Diptera. Moreover, differential activation of these metabolic pathways in the course of ontogenesis brings about a marked temporal compartmentalization. Many phases of tyrosine biochemistry are thus recognized in the development of Lepidoptera.[Journal translation]