The initial synthesis of proteins during development. Phosphoenolpyruvate carboxylase in rat liver at birth.

1. A specific antibody, prepared by immunizing rabbits with phosphoenolpyruvate carboxylase (EC 4.1.1.32) purified from adult rat liver, was used to study the appearance of this enzyme in livers from developing rats. 2. Although some inactive precursor of the enzyme may be present in foetal liver, the amount is not sufficient to account for the enzyme appearance at birth. 3. The rate of phosphoenolpyruvate carboxylase synthesis relative to other cytosol proteins increases 20-fold from the foetus to the 1-day-old rat. The high rate of synthesis was maintained at least until 3 days after birth. 4. There was no measurable degradation of phosphoenolpyruvate carboxylase during the first day after birth. During this period the hepatic enzyme content increased 12-fold. 5. When phosphoenolpyruvate carboxylase attained a constant activity in the liver of rats 2 days after birth the half-time of degradation was approx. 13h. 6. We suggest that the pattern of changes occurring during appearance of phosphoenolpyruvate carboxylase is similar to substrate-induced enzyme induction in bacteria.