Hydroxykynureninuria: A case of Abnormal Tryptophan Metabolism Probably Due to a Deficiency of Kynureninase

Abstract

During the past decade the route by which tryptophan is converted to nicotinamide has been well studied, but the later stages of the conversion have yet to be fully explained. This tryptophannicotinamide transformation has been shown to occur in mammals (Rosen, Huff and Perlzweig, 1946) and later the formation of labelled nicotinic acid from C14-labelled tryptophan was demon- strated by Heidelberger, Abraham and Leprovsky (1949). Kotake and Nakayama (1941) and Dalgliesh, Knox and Neuberger (1951) showed that, along this series of reactions, the conversion of kynurenine to anthranilic acid and of 3-hydroxykynurenine to 3-hydroxyanthranilic acid was, in each instance, catalysed by the same enzyme, namely kynureninase. Charconnet-Harding, Dalgliesh and Neuberger (1953) found that in addition to kynurenine, kynurenic acid and xanthurenic acid, 3-hydroxykynurenine was excreted on administra- tion of tryptophan to rats fed on a low pyridoxin diet.