Teiichi Eto

Nutrition of Threonine: Part VIII. Actinomycin-Insensitive Induction of Rat Hepatic Threonine Dehydratase and Its Reversal by Growth Hormone

Tryptophan was found to be a factor that enhanced rat hepatic threonine dehydratase activity without resulting from increase in gluco-corticoid secretion. If rats were fed on tryptophan added diet prepared by adding 140 mg/day tryptophan to 20g/day 20% casein diet, the resulting threonine dehydratase activity was about 1.5 times as much as that observed in rats fed 20% casein diet. If adrenalectomized rats were used, the similar results were obtained. In the case of hypophysectomized rats, however, about 4 times the activity was observed. This enormous increase in the activity was mostly prevented by growth hormone. This hormone was also effective in preventing the tryptophan-aided increase in threonine dehydratase activity of intact rats. Thyroxine was ineffective in preventing the activity increase. Either actinomycin S3 or puromycin treatment on rats disclosed that the trvptophan-aided activity increase was based on de novo synthesis of the enzyme through the translational step, not through the transcr...