The prematurely evoked synthesis of liver tryptophan oxygenase

Livers of normal rats are devoid of catalytically or immunochemically reactive tryptophan oxygenase (EC 1.13.1.12) up to the 10th postnatal day; the enzyme reaches adult concentrations on about the twentieth day. Premature tryptophan oxygenase synthesis can be evoked in 4-day-old rats: if an injection of glucocorticoid is followed, a day later, by an injection of tryptophan, adult levels of tryptophan oxygenase activity and antigen content can be attained within 5 hr. The prematurely evoked tryptophan oxygenase is degraded in about 2 days, but the preparatory action of the glucocorticoid is longlasting. Even 4 days later, an injection of tryptophan can evoke significant enzyme formation. Actinomycin D, injected together with or 12 hr before the tryptophan, is not inhibitory, but if injected with the glucocorticoid it prevents enzyme formation upon later injection of tryptophan. The observations suggest that appearance of the new enzyme in developing tissue results from the sequential action of more than one stimulus and that the potentiality for its transcription may develop long before its actual synthesis.