Premature induction of hepatic tryptophan oxygenase

Subcutaneous administration of hydrocortisone acetate to the newborn rat produces a premature induction of hepatic tryptophan oxygenase consisting of a transient rise in activity 6–8 h after treatment, followed by a second sustained rise beginning 40 h later, which plateaus at 10 days of age. Cycloheximide treatment at the midpoint of this second elevation inhibits protein synthesis, but not tryptophan oxygenase activity. In older animals, cycloheximide treatment does both. Tryptophan administration at this midpoint rapidly elevates tryptophan oxygenase activity. This elevation can be partially blocked by treatment with actinomycin D within 1 h of tryptophan administration, but not thereafter. Actinomycin treatment is ineffective in blocking the tryptophan-induced rise in older animals. Administration of hydrocortisone acetate to 5- and 10-day-old pups leads to a more rapid and sustained rise in tryptophan oxygenase activity without appearance of a transient induction phase. Neither tryptophan alone, -aminolevulinic acid alone, nor tryptophan plus -aminolevulinic acid prematurely induces tryptophan oxygenase in newborn or 5-day-old rats.     

Effects of pyrazole on rat liver tryptophan oxygenase

The effects of pyrazole administration on rat liver tryptophan oxygenase have been studied both under basal conditions and after induction by cortisol or activation by tryptophan.Pyrazole administration is followed by a decrease of the basal holoenzyme and total enzyme activities. It induces furthermore a considerable inhibition of the cortisol mediated tryptophan oxygenase induction. These effects are not mediated by a modification of a tryptophan oxygenase effector, as shown by mixed homogenate experiments. The tryptophan enhancement of total tryptophan oxygenase activity is not affected by pyrazole administration contrary to the holoenzyme activity. Pyrazole added $\text{in vitro}$ inhibits liver tryptophan oxygenase activity only when used at concentrations which are considerably higher that those occuring $\text{in vivo}$ after pyrazole administration.     

Dexamethasone control of the development of tryptophan oxygenase in young rats

Tryptophan 2, 3-dioxygenase activity follows a characteristic pattern of change during development of suckling rats; namely, it is appears 2 weeks after birth and then increases to the adult level by day 22. Glucocorticoids, potent inducers of the enzyme in adult rats, can induce its precocious appearance on day 8 or 10 after birth (1) or even on day 4 (2). The induced level is not more than the adult basal level. We investigated the conditions controlling the response to glucocorticoid before day 14 in suckling rats without using tryptophan. Pretreatment with dexamethasone for 2 days increased the induction by glucocorticoid, resulting in 2 to 3 times higher activity than the adult basal level. Actinomycin D and cycloheximide inhibited this enzyme induction.     

Activation of liver tryptophan oxygenase by hydrocortisone, hematin and tryptophan in streptozotocin-diabetic rats

This study compared changes in liver tryptophan oxygenase (TPO) activity in response to hydrocortisone, hematin and tryptophan administration to non-diabetic and diabetic (streptozotocin) rats. Hydrocortisone caused similar increases in apoenzyme (inactive), holoenzyme (heme-saturated) and total (holoenzyme + apoenzyme) TPO activities in non-diabetic and diabetic rats. The ability of hematin to increase total TPO activity was significantly less in diabetic rats. The largest differences between diabetic and non-diabetic rats were found with tryptophan which increased total TPO and holoenzyme activities 300% and 650% respectively in non-diabetic rats. However, tryptophan increased both apoenzyme (unchanged in non-diabetic rats) and holoenzyme activities by 300% in diabetic rats. These results indicate that in the diabetic state, the TPO-heme conjugation process is impaired, especially substrate mediated TPO-heme saturation.     

Purification of tryptophan oxygenase and its interaction with cadmium

Purification of tryptophan oxygenase (L-tryptophan oxidoreductase EC 1.13.1.12) from $\text{Pseudomonos acidovorans}$ is described. When chromatographed on Sephadex G-200 or on DEAE Sephadex A-50, the enzyme was eluted in two distinct bands. Over the concentration range 10^?6 – 10^?4 M, cadmium stimulated the activity of the enzyme but inhibited it non-competitively at higher concentrations. A mechanism is suggested for the behaviour of the enzyme towards cadmium.     

A specific and sensitive fluorometric assay for tryptophan oxygenase

A spectrophotofluorometric assay was used to measure tryptophan oxygenase activity in several species. The fluorescent assay depends on the conversion of the product of the reaction, N-formyl-l-kynurenine, to anthranilate by means of the coupling enzymes kynurenine formamidase and kynureninase. These enzymes are easily obtained from l-tryptophan-induced N. crassa; and the product, anthranilate, is readily separated by organic extraction from other tryptophan catabolites and easily identified fluorometrically. With this assay, tryptophan oxygenase has been demonstrated in vitro for the first time in N. crassa.