Tryptophane Metabolism in Rice Moth Larva (Corcyra cephalonica St.)

Abstract

EARLIER workers¹, who observed the excretion of the tryptophane metabolites, kynurenine and xanthurenic acid, by the rat and the rabbit under conditions suggestive of vitamin B deficiency, failed, however, to realize its physiological significance. It was not until Lepkovsky et al. ² isolated and identified the pigment metabolite, xanthurenic acid, from the urine of pyridoxine-deficient rats receiving extra-dietary tryptophane, that the role of this vitamin in the metabolism of the amino-acid was unequivocally established. Since then, a number of reports have appeared of the conversion of tryptophane to xanthurenic acid, kynurenine, hydroxykynurenine, etc., by pyridoxine-deficient rats, rabbits and dogs^1,3. In 1945, Sarma⁴ found that the rice moth larva (Corcyra cephalonica St.), maintained on a pyridoxine-deficient diet containing added tryptophane, excreted yellow-coloured fæces. This was about the first and only report on the role of pyridoxine in tryptophane metabolism in insects and established a striking parallel in the metabolism of the amino-aoid between mammals and insects. Pyridoxine had earlier been shown by the same author⁵ to be an essential vitamin for the growth of the larva. The excretory pigment, however, was not characterized; but it was shown that it was not identical with xanthurenic acid, from the negative test it gave with iron salts, Tryptophane, has also been shown to be the precursor of the pigments, ommochromes, found in the eyes and tissues of certain insects, and the production of the pigments; appears to be controlled by genes⁶. Kynurenine and hydroxykynurenine, which are normal intermediates in this conversion, and kynurenic acid, which is derived from kynurenine by oxidative deamination consequent on a gene mutation, have all been identified and isolated^6–9. The present communication outlines further studies of the metabolism of tryptophane in the rice moth larva. The effect of the incorporation of DL-kynurenine and of D-tryptophane in the diet instead of DL-tryptophane and the chemical identity of the excretory pigment have been investigated.