Ommochrome Genesis in an Albino Strain of a Terrestrial Isopod

The contents of tryptophan (Trp) metabolites and the activities of the enzymes involved in ommochrome biosynthesis were measured in an albino strain of a terrestrial isopod Armadillidium vulgare. There was little difference between the Trp content in the albino mutant and that in the wild type, although the contents of 3-hydroxykynurenine (3-OH-Kyn), 3-hydroxyanthranilic acid (3-OH-AA) and xanthommatin in the albino were significantly lower than those in the wild type. Tryptophan 2,3-dioxygenase (TDO) activity in the albino was extremely low, while the activities of Kyn-3-hydroxylase and kynureninase did not differ significantly between the two phenotypes. The extremely low activity of TDO is probably one of main reasons why almost no ommochrome pigment is produced in the albino mutant.