Tryptophan accumulation and tryptophan pyrrolase induction in rat liver as a function of age

Abstract The kinetics of tryptophan uptake and tryptophan pyrrolase induction in the livers of 1- and 6-month-old rats were studied in order to ascertain whether the observed age-related alteration of induction is the result of changes in the pattern of substrate accumulation with age. The initially faster rate of appearance of the enzyme in the youngest group was not paralleled by a more rapid uptake of the amino acid. Instead, considerably more tryptophan was present per gram liver of the 6-month-old rats during the initial phase of induction. The rate of increase of enzyme activity began to diminish in 1-month-old rats at the same intracellular concentration of tryptophan which was followed, in the older rats, by an unabated increase in enzyme level. These findings suggest that the enzyme is synthesized and inactivated or catabolized more rapidly in the young growing rats.