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SUMMARY The kynureninase activity measured in dialysed homogenates of rat liver at various time intervals after hypophysectomy or adrenalectomy was always decreased. This behaviour reminds one of other PLP-dependent activities. The administration of extra tryptophan to hypophysectomized or adrenalectomized rats did not alter the liver kynureninase levels. Thus, in these experimental conditions, as in the normal rat, kynureninase could not be induced by tryptophan. PLP added in vitro to liver preparations of hypophysectomized or adrenalectomized rats increases the kynureninase; however, it does not restore this activity to normal. The activity variation was in all cases of the same order in normal and operated rats. Therefore the ability of the enzyme to bind the coenzyme was unaltered in the liver of hypophysectomized or adrenalectomized rats.

The tryptophan metabolism in rats after hypophysectomy or adrenalectomy has been studied. In animals kept on a complete diet there was a diminution of kynurenine and diazotizable substances after removal of one of the glands under consideration (the urinary concentrations of these metabolites reach normal values only after 19 days from hypophysectomy). Elimination of xanthurenic acid increases after hypophysectomy and decreases after adrenalectomy; in this latter case it is accompanied by an increase in nicotinic acid. In pyrixodine-deficient animals urinary elimination of kynurenine is lower after adrenalectomy; a supplement of pyridoxine restores it to normal.

Viene dimostrata la presenza di attivita triptofano pirrolasica nell'omogenato e nel sopranatante ottenuti da campioni di fegato di neonati a termine e di adulti. Nel fegato di neonati immaturi questa attivita enzimatica e risultata assente anche nelle prove di attivazione mediante aggiunta di microsomi di fegato.