Analysis of kynurenine transaminase activity in Drosophila by high performance liquid chromatography

A sensitive assay for kynurenine transaminase activity (E.C. 2.6.1.7) based on rapid separation of the reaction product by high performance liquid chromatography (HPLC) has been developed. Drosophila sordidula extracts have been assayed by this new method and this is the first time that kynurenine transaminase activity has been demonstrated in Drosophila. The method of assay developed can be extended to any other organism. Kynurenine and 3-hydroxykynurenine were both used as substrates, and they were transaminated to kynurenic acid and xanthruenic acid, respectively. HPLC is used to separate and quantitate these reaction products from all other components in the reaction mixture.

In crude extracts from Drosophila, the reaction requires pyridoxal 5′-phosphate and an amino acid acceptor. The enzyme activity showed a maximum at 47°C and pH 8.0 with kynurenine and pyruvic acid as substrates. Transaminase activity was present in both head and body, nevertheless the specific activity was higher in the former. In bodies, pyruvic acid was the best amino acceptor whereas in heads it was α-oxoglutaric acid. The variation of kynurenine transaminase during development of D. sordidula showed, in the larval and pupal stages, activity levels practically constant and much lower than those found in the adult. This seems to suggest a preferential role of this enzyme in the metabolism of intermediates in the biosynthesis of ommochromes.