Induction of glutamine synthetase of the liver of young and old rats

Abstract

1. The induction of glutamine synthetase of the liver by cortisone was studied in young (9-10 weeks) and old (60-70 weeks) intact, adrenalectomized and hepatectomized rats. 2. There was no significant difference in the activity of the enzyme of young and old normal rats. Cortisone induced the enzyme in both young and old intact rats. Bilateral adrenalectomy caused a greater inhibition of the activity of the enzyme in the old animals. Administration of cortisone to adrenalectomized rats caused greater induction of the enzyme in old rats. This induction was inhibited by actinomycin D. 3. Partial hepatectomy resulted in a decrease in the activity of the enzyme in both young and old rats equally. Cortisone caused greater induction of the enzyme in the regenerating liver of the young animals. This induction was also inhibited by actinomycin D. 4. The K_m (glutamine) of purified glutamine synthetase of old rats was 2.5-fold higher than that of young rats. Carbamyl phosphate and UMP inhibited the activity of the enzyme equally at both ages.