Hydroxykynurenine and Insect Eye Pigments

The identification of hydroxykynurenine as the cn+-substance which is the precursor of insect eye pigments (ommochromes) has already been described. Ommochromes had previously been considered to be pterin derivatives (140, 534), but there is no obvious route for the conversion of hydroxykynurenine to the pterin type of structure. However, pterins also occur in insect eyes (275). More recent work has shown that the eye pig- 

The phenoxazine can then participate in reversible oxidation-reduction reactions, and moreover by transamination and cyclization of one side chain, in a manner analogous to xanthurenic acid formation discussed below, can give a pyridinophenoxazine derivative which equally undergoes reversible oxidation-reduction, and which, being a derivative of 8-hydroxy-quinoline, would bind metals strongly (see also 122a). 

Kynurminase, Kynurenine Transaminase, and the Formation of Anthranilic, Kynurenic, Hydroxyanthranilic, and Xanthurenic Acids 

Reference has already been made to the abnormally high excretion of kynurenine and xanthurenic acid in pyridoxine deficiency. This was confirmed by many workers (e.g., 372, 599, 620, 674, 698, 732), and the reason for it became evident from enzymic experiments. 

The first mention of enzymic conversion of kynurenine to kynurenic 

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