Phenylalanine hydroxylase activity in foetal hepatic organ culture (original) (raw)

The biphasic pattern of phenylalanine hydroxylase (L-phenylalanine tetrahydropteridine:02 oxidoreductase (4-hydroxylating) EC 1.14.3.1) activity of foetal and neonatal rat liver is not observed in 2o-to 22-day-old hepatic explant culture. Two genetic markers of differentiated hepatic tissue were used to monitor hepatic explant: (a) a high baseline tyrosine aminotransferase activity (L-tyrosine:2-oxoglutarate aminotransferase, EC 2.6.1.5); and (b) hydrocortisone inducibility of this activity. Pre-existing phenylalanine hydroxylase activity of 22-day-old foetal explants decays with a half-life of 6 h. These observations suggest the need for a hepatic or extrahepatic inductive signal for the synthesis of phenylalanine hydroxylase.