STUDIES ON MECHANISM OF INDUCTION OF TYROSINE AMINOTRANSFERASE IN NEONATAL RAT LIVER

Postnatal induction of tyrosine aminotransferase (L-tyrosine 2-oxoglutarate aminotransferase EC 2.6.1.5) in rat liver is prevented by adrenalectomy, and hydrocortisone induction in such animals is prevented by actinomycin D. Glucagon injection to fetal rats in utero induces enzyme only when endogenous adrenal steroid levels are high but catecholamines and 3′,5′-cyclic adenosine monophosphate do not induce activity. Normal postnatal synthesis of the enzyme is slightly repressed by ergotamine tartrate, prostaglandin, insulin, and pyridoxine and is increased by repeated injection of glucagon or 3′,5′-cyclic adenosine monophosphate. Insulin and pyridoxine induce increased activity in 2-day postnatal animals. In 4-hr and 2-6-day postnatal animals induction of enzyme activity by 3′,5′-cyclic adenosine monophosphate is insensitive to actinomycin D and induction by epinephrine in 2-6-day animals is only marginally sensitive to the antibiotic. Thus, hormonal induction of tyrosine aminotransferase mediated through 3′,5′-cyclic adenosine monophosphate appears to operate at the level of translation in enzyme synthesis. It is suggested that apparent multiple inductive pathways for tyrosine aminotransferase in both fetal and adult animals may be explained in terms of the discrete induction of different forms of the enzyme. © 1969, American Chemical Society. All rights reserved.