Influence of beta-alanine on ultrastructure, tanning, and melanization of Drosophila melanogaster cuticles.

In Drosophila melanogaster, the chitinous microfibrils arising from the tips of the epidermal villi in adult cuticles remain irregular and loose in the mutant ebony (which fails in cuticular incorporation of beta-alanine) but closely knit and regular in normal flies. Addition of beta-alanine to cuticles from which nonchitinous materials have been removed with alkali converts the loose arrangement of the microfibrils to a compact and sharply delineated arrangement. beta-alanine also accelerates tyrosinase-catalyzed oxidation of N-acetyldopamine by reacting with the oxidized product of the reaction to produce an orange-red complex. Similarly, beta-alanine accelerates oxidation of N-acetyldopamine when these two substances are added to fluids from the hemocoel, to lead to tanning instead of normal blackening. These findings may help explain why beta-alanine induces tanning while inhibiting melanization in insects.