Tryptophan degradation in the developing chick

Abstract

The level of tryptophan pyrrolase, the first enzyme involved in the degradation of tryptophan, is not increased during development of the chick. The level of kynurenine formamidase, the second enzyme involved in tryptophan degradation, does increase dramatically coincident with hatching. Administration of tryptophan to chick embryos does not result in increased levels of tryptophan pyrrolase whereas administration of tryptophan to newly hatched chicks does result in enzyme induction. Administration of hydrocortisone to either chick embryos or to newly-hatched chicks has no effect on the level of tryptophan pyrrolase. Studies carried out with inhibitors of protein synthesis indicate that the turnover of tryptophan pyrrolase is slower in the chick embryo than in the newly-hatched chick. These turnover studies were carried out with intact animals and with isolated liver cells. These results are consistent with the concept that administered tryptophan stabilizes the enzyme and that the rise in enzyme level is not due to an increased rate of enzyme synthesis but, rather, to a decreased rate of enzyme destruction. This effect is not seen when the half-life of the enzyme is increased.