Accumulation of kynurenic acid in the “cinnabar” mutant of Drosophila melanogaster as revealed by thin-layer chromatography

Abstract

From a study of chromatograms run on extracts from over 80 different eye colour mutants and the wild type of Drosophila melanogaster, only in the case of the cinnabar mutant was evidence for an unknown compound found. From its chromatographic behaviour, u.v. absorption spectra and other characteristics joined to metabolic considerations, it was identified as kynurenic acid. This agrees with the metabolic lesion of the mutant cinnabar which does not possess the normal kynurenine hydroxylase enzyme which oxidizes kynurenine to 3-hydroxykynurenine, so in this mutant kynurenine is largely transformed into kynurenic acid. When cn-double mutants were tested it was found that kynurenic acid was not accumulated. Only in st cn was it found to acculate. The blockage of the xanthommatin pathway and high levels of red pigment seems to be the conditions required for the accumulation of kynurenic acid. The accumulation of this metabolite occurs in the head and begins with the formation of the eyes, reaching the highest level on the first day after emergence and remaining approximately constant throughout its life. This fact coincides with the development and deposition of eye pigments and suggests that its accumulation is due to the metabolism of them and not to the general metabolism of tryptophan in the insect.