Oxidation of 3-hydroxykynurenine to produce xanthommatin for eye pigmentation: a major branch pathway of tryptophan catabolism during pupal development in the Yellow Fever Mosquito, Aedes aegypti

This study concerns the metabolic pathways of 3-hydroxykynurenine in Aedes aegypti mosquitoes during development with emphasis on its oxidation pathwa y to produce xanthommatin during eye pigmentation. Oxidation of tryptophan to 3-hydroxykynurenine is the major pathway of tryptophan catabolism in Aed es aegypti, but 3-hydroxykynurenine oxidizes easily under physiological con ditions, which stimulate the production of reactive oxygen species. Our dat a show that in Aedes aegypti, the chemically reactive 3-hydroxykynurenine i s converted to the chemically stable xanthurenic acid by a transaminase-cat alyzed reaction during larval development, while 3-hydroxykynurenine is tra nsported to the compound eyes for eye pigmentation during pupal development Our data suggest that (1) the transamination pathway of 3-hydroxykynurenin e is down-regulated during the pupal development, (2) 3-hydroxykynurenine p roduced in other body tissues is actively transported to the compound eyes during the pupal stage, (3) the compound eye is the place where ommochromes are produced, and (4) formation of ommochromes results from nonenzymatic o xidation of 3-hydroxykynurenine in the compound eyes. (C) 1999 Elsevier Sci ence Ltd. All rights reserved.