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Journal of Nutrition Vol. 101 No. 10 October 1971, pp. 1351-1358
Copyright © 1971 by American Society for Nutrition
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Inversion in the Metabolism of D-Tryptophan in the Rabbit and the Rat1

Horace H. Loh and Clarence P. Berg2

Department of Biochemistry, College of Medicine, University of Iowa, Iowa City, Iowa 52240

The production of L-tryptophan and L-kynurenine upon incubating D-tryptophan with liver slices and homogenates from the rabbit and the rat suggested that the kynurenic acid formed from D-tryptophan may have arisen partly through them and partly via D-kynurenine. Kidney slices and homogenates produced L-tryptophan even more readily, but yielded neither D- nor L-kynurenine. The L- and D-isomers of tryptophan and kynurenine were separated and identified by paper chromatography, and assayed quantitatively. Their configurations were confirmed by their reaction with L- or D-amino acid oxidase to yield indolepyruvic acid or kynurenic acid. The production of L-tryptophan from the D-tryptophan occurred in two steps. The first step required oxygen. It yielded indolepyruvic acid under conditions optimal for D-amino acid oxidase activity. The second step involved the conversion of the indolepyruvic acid to L-tryptophan, either in the presence or absence of oxygen, under conditions favoring transamination. Rat tissues effected the overall inversion more readily than rabbit tissues. Differences in the capacities of rat versus rabbit tissue to deaminate the D-tryptophan were more marked than the differences in their capacities to transaminate the indolepyruvic acid. Production of kynurenic acid through oxidative deamination of D-kynurenine and through transamination of L-kynurenine were indicated.

1 The data presented are from the dissertation submitted by Horace H. Loh in partial fulfillment of requirements for the degree of Doctor of Philosophy in Biochemistry in the Graduate College of the University of Iowa. The support given us by the National Institute of Arthritis and Metabolic Diseases through U.S. Public Health Service Grants AM-01770 and AM_0979 is gratefully acknowledged. A preliminary report has been published (Loh, H. H., and C. P. Berg 1964 Metabolism of D-tryptophan. Federation Proc. 23: 421 (abstr. no. 1916).

2 To whom inquiries should be sent.

Manuscript received 22 March 1971.




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