Effect of Ethionine on the Cortisone-Evoked Stimulation of Tryptophan Peroxidaseoxidase Activity¹

The activity of tryptophan peroxidase-oxidase was studied in rat liver following intraperitoneal injections of cortisone, ethionine, and methionine. Cortisone elicited the expected increase in activity, a dose of 50 mg. per kg. evoking a five-fold stimulation. Ethionine and methionine (0.77 mM.), on the other hand, did not alter the activity of this enzyme. Administration of ethionine with cortisone greatly reduced the stimulatory effect of the hormone. Coadministration of methionine with ethionine (both at a dosage of 0.77 mM.) restored the ability of cortisone to stimulate tryptophan peroxidase-oxidase activity. These results are taken to support the hypothesis that a de novo synthesis of this enzyme, believed to occur as a result of tryptophan administration, may also occur following the administration of cortisone.