The activation and induction of rat liver tryptophan pyrrolase in vivo by its substrate.

Parenteral administration of tryptophan has been shown to increase markedly rat liver tryptophan pyrrolase activity (1). This phenomenon is often referred to as induction or adaptation due to its similarity to substrate-induced enzyme formation in microorganisms. The preceding article (2) documents the presence of a factor in microsomes which activates tryptophan pyrrolase of normal liver cell sap. Preliminary experiments have been reported which show that after tryptophan treatment, the elevated level of liver cell sap tryptophan pyrrolase, unlike that of normal cell sap, cannot be stimulated further by this microsomal activator (3). These phenomena have now been further investigated and their relevance to the substrate-induced elevations of rat liver tryptophan pyrrolase activity has been esplored.