The enzymes of phosphatidylcholine biosynthesis in the fetal mouse lung: Effects of dexamethasone

Abstract

1. 1. The present study presents the activity profiles of the enzymes involved in the formation and utilization of CDPcholine at different stages of development of the mouse lung. 2. 2. The specific activity of choline kinase (EC 2.7.1.32) remained at a constant level during the later stages of fetal development and decreased postnatally. 3. 3. Cholinephosphate cytidylyltransferase (EC 2.7.7.15) is localized both in the cytosol and microsomal fraction of the mouse lung. In the adult lung the majority of this enzyme is found in the cytosol, whereas in the fetal lung the enzyme is distributed almost equally between microsomes and cytosol. The specific activity of the soluble enzyme increases strongly around two days before term and remains at this level until at least three days after birth. The microsomal enzyme showed a similar profile except that the increase started one day later. 4. 4. In agreement with a previous study, it was found that cholinephosphotransferase (EC 2.7.8.2), which catalyzes the conversion of CDPcholine into phosphatidylcholine, increases during the later stages of fetal lung development until it reaches a maximal specific activity at two days before term. 5. 5. The hydrolysis of CDPcholine into phosphocholine and CMP is relatively unimportant in the microsomes of fetal lung but becomes prominent in the adult lung. 6. 6. Glucocorticosteroids are known to accelerate maturation of the fetal lung and production of surfactant. In the present study it could be shown that dexamethasone, injected into mice on day 14 of the pregnancy, elicited a significant increase in the specific activity of cholinephosphotransferase in the fetal lung on days 17 and 18. The corticosteroid did not affect the specific activities of choline kinase or cholinephosphate cytidylyltransferase. Treatment with dexamethasone also resulted in enhanced specific activities of lysophosphatidylcholine acyltransferase (EC 2.3.1.23) an enzyme which may play an important role in the conversion of unsaturated phosphatidylcholines into 1,2-dipalmitoyl- sn-glycero-3-phosphocholine. It did not, however, affect the specific activity of lysophosphatidylcholine : lysophosphatidylcholine acyltransferase.