The specificity of tryptophan analogues as inducers, substrates, inhibitors, and stabilizers of liver tryptophan pyrrolase.

In animals, liver tryptophan pyrrolase was induced independently by administration of its substrate L-tryptophan (I), and of the hormone hydrocortisone (2). Some analogues of tryptophan which are not substrates of the tryptophan pyrrolase, such as c+mcthyl-DL-tryptophan (3) and D-tryptophan,’ have been reported to induce the enzyme in intact animals. Since a substance may cause enzyme induction in viva by stressinduced adrenal secretion and the hormone-induced mechanism, adrenalectomized rats were used to determine the specificity of the substrate-induced enzyme response. The same analogues of tryptophan also were tested as substrates, inhibitors, and stabilizers of the cell-free enzyme preparation to determine whether there was any relation between the inducing activity of a substance and its affinity for the enzyme.