Insect pigmentation: activities of beta-alanyldopamine synthase in wing color patterns of wild-type and melanic mutant swallowtail butterfly Papilio glaucus.

Abstract

Color pattern formation was studied in wild-type and melanic swallowtails because of their unique pigment system, the papiliochromes, which are derived from the tyrosine as well as from the tryptophan pathway. In a comparative approach we used females of Papilio glaucus which occur in two phenotypes, either wild-type (yellow and black) or melanic. Pigment synthesis in the developing wings starts with formation of yellow papiliochromes followed later by black melanin. From earlier studies we know that dopamine produced from DOPA by the enzyme dopadecarboxylase (DDC), is a precursor of both black melanin and also of N-beta-alanyldopamine (NBAD) in yellow papiliochrome synthesis. Thus, DDC expression and enzyme activity is required in both types of pigment forming scale cells and occurs in a time and pattern specific manner. However, differential activity of DDC alone can not be sufficient to regulate synthesis of different pigments in differently colored scales. Therefore, we tested the hypothesis whether activity of another enzyme, beta-alanyldopamine synthase (BAS), regulates specifically papiliochrome synthesis. BAS transfers beta-alanine to dopamine to give NBAD a component of yellow papiliochrome. We developed a radio-enzyme-assay of BAS activity in which (14C)-beta-alanine is incubated with dopamine, Mg++-ions and ATP together with wing homogenates containing putative BAS activity. In fact, high BAS activity was measured in yellow wings in concert with a high DDC activity. In contrast, in melanic wings almost no BAS activity was found. From this result it is clear, that papiliochrome synthesis in yellow scales is switched on by BAS shifting dopamine into the papiliochrome pathway and out of the melanin pathway or vice versa.