The relation of liver kynureninase to tryptophan metabolism in pyridoxine deficiency

Abstract

Under optimal conditions the avg. kynureninase activity of normal rat liver removed 11.1/u moles L-kynurenine/g. dry wt./hr. In pyridoxine-deficient rats the activity was decreased to 5.9 [mu]moles/g. dry wt./hr. The kynureninase was not increased adaptively in the animals by admn. of kynurenine or tryptophan. By contrast, kynurenine can be formed by tryptophan peroxidase in normal rat liver at an avg. rate of 9.3 [mu]moles/g. dry wt./hr., and this rate can be adaptively increased 10-fold by tryptophan admn. to the animal. The abnormal accumulation of tryptophan metabolites can, therefore, be attributed to relative inadequacy of kynurenine removal, due to a decrease of kynureninase activity, to an adaptive increase of tryptophan peroxidase, or to both. These mechanisms can account for the marked accumulation of metabolites in normal animals given supplemental tryptophan, as well as in pyridoxine-deficient animals.