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D-Tryptophan Pyrrolase Activity in the Liver and the Intestine of the Rat¹

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

Recent stereospecific assay methods have shown that contrary to earlier negative claims, rabbit and rat liver slices and homogenates do convert D-tryptophan to D-kynurenine. The procedures have also shown that extracts of rabbit intestine convert D-tryptophan to D-kynurenine and L-tryptophan to L-kynurenine. Protocols recorded in the current paper seem to indicate that the liver enzyme which initiates the production of D-kynurenine from D-tryptophan is either identical with L-tryptophan pyrrolase or at least strikingly similar. Its activity, like that of L-tryptophan pyrrolase, was markedly stimulated by prefeeding or preinjecting D- or L-tryptophan or preinjecting cortisone in normal and adrenalectomized rats whose livers were to be assayed. Tests of fractionated homogenates from normal rats showed that the activity was confined to the cell sap, but was enhanced by adding aliquots of the microsomal fraction. The data agreed qualitatively with those published for L-tryptophan pyrrolase. Pyrrolase found in the intestinal mucosa of rats was less active than the intestinal "D-tryptophan pyrrolase" previously observed in rabbits. It attacked L-tryptophan almost as readily as D-tryptophan. In comparison with the rat liver pyrrolase, the activity of the intestinal pyrrolase was only moderately stimulated by prefeeding D-tryptophan or preinjecting cortisone.

KEY WORDS: • D-tryptophan • D-kynurenine production • liver pyrrolase • intestinal pyrrolase • pyrrolase induction

¹ Parts of the data are from a dissertation submitted by Horace H. Loh in partial fulfilment of requirements for the degree of Doctor of Philosophy in Biochemistry in the Graduate College of the University of Iowa. The authors are indebted to the National Institute of Arthritis and Metabolic Diseases for the financial support given by U.S. Public Health Grants AM 01770 and AM 09797. A preliminary report of the earlier phase of the study has been presented: Loh, H. H., and C. P. Berg 1964 Metabolism of D-tryptophan. Federation Proc. 23: 421 (abstr. no. 1916).