Changes in CTP:phosphatidate cytidylyltransferase activity during rabbit lung development.

The specific activity of CTP:phosphatidate cytidylyltransferase in rabbit lung and liver microsomes during fetal and neonatal development has been measured. The enzyme in the microsomal fraction of lung tissue has a requirement for Mg2+. Optimal enzyme activity is achieved with phosphatidate (4 mM) and CTP (2 mM) in the presence of ATP (6 mM). Analysis of the reaction products demonstrates that the ATP serves to inhibit the hydrolysis of CTP by microsomal pyrophosphatases. The specific activity of the microsomal enzyme remains constant from day 23 through day 28 of gestation, then increases 2.4-fold between day 28 and day 1 post-partum. The specific activity of the enzyme in the microsomal fraction from rabbit liver tissue does not change significantly, and is less than in the lung tissue at all stages of development. The increase in the activity of microsomal CTP:phosphatidate cytidylyltransferase in lung tissue is concurrent with the appearance of pulmonary surfactant containing phosphatidylglycerol during the perinatal period of rabbit lung development.