An analysis of the kinetics of rat liver tryptophan pyrrolase induction: The significance of both enzyme synthesis and degradation

The fact that the levels of numerous enzymes in mammalian tissues can be increased by the administration of specific substrates and hormones is well established (Knox and Mehler, 1951; Greengard and Feigelson, 1961;Lin and Knox, 1957; Schimke, 1962; Conney and Gilman, 1963). Such increases superficially resemble bacterial enzyme induction, but may in fact result from different mechanisms. Previous studies from this laboratory (Schimke et al., 1963) have indicated that a decrease in the rate of enzyme degradation, i.e., enzyme stabilization, is an important control mechanism for rat liver arginase. In this paper an analysis of the kinetics of increases in rat liver tryptophan pyrrolase produced by corticosteroids and tryptophan is presented. The results provide further evidence that in mammalian tissues the level of a specific enzyme is controlled by the rate of enzyme degradation, as well as by the rate of enzyme formation.