The development of pyruvate carboxylase in rat liver mitochondria

Enzymatic and immunologic methods were used in the studies of the development of mitochondrial pyruvate carboxylase (PC) in the perinatal rat liver. Rabbit antibodies to purified rat liver mitochondrial PC and to rat liver mitochondria were made. The monospecific activity of the anti-PC serum was demonstrated. Results of the study of developmental PC formation showed a simple quantitative change in PC activity and PC protein. A minute amount of PC (0.10-0.45 mumol/g liver/min; 2-10 mug/g liver) in fetal liver mitochondria increased to 1.9 +/- 0.12 mumol/g/min; 60 +/- 4 mug/g at 4-5 hr after birth, peaked (7.11 +/- 0.50 mumol/g/min; 175 +/- 12 mug/g) on the fifth day, and then declined to the normal level (4.68 +/- 0.42 mumol/g/min; 130 mug/g) found in adult liver during the third week. Results of the studies concerning the effects of premature and postmature delivery on the developmental pattern of PC during the first 8 hr after birth suggest that the postnatal increase of this enzyme is not triggered by the process of birth itself. Speculation The increase of mitochondrial PC activity and PC protein in the neonatal liver will lead to a greater availability of glucogenic carbon in the cytosol and will make a significant contribution to the overall enhancement of neonatal gluconeogenesis.