Activities of the phosphatidylcholine biosynthetic enzymes in rat liver during development

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Abstract
The activities of the enzymes of rat hepatic phosphatidylcholine biosynthesis have been measured as a function of development in the rat (term, 23 days). During the last 5 days of gestation, the specific activity of choline kinase was elevated almost fivefold (p < 0.05). After parturition, choline kinase activity was reduced to adult values by the 5th postnatal day. Over 75% of the total CTP:phosphocholine cytidylyltransferase protein in prenatal liver was detected in the cytosolic fraction. On the day of birth, most of the cytidylyltransferase translocated to the microsomes so that the microsomal specific enzyme activity was 3.3-fold higher (p < 0.01) and the cytosolic specific enzyme activity (measured in the presence of phospholipid) was 68% lower (p < 0.001) than the day before parturition. CDPcholine:diacylglycerol cholinephosphotransferase activity (measured in the presence of diacylglycerol) increased 130-fold (p < 0.001) during the last 5 days of gestation. On the 10th postnatal day, cholinephosphotransferase activity was 1.7-fold higher (p < 0.001) than immediately after birth, but declined to adult values by the 19th day. Between the 5th day prior to parturition and the 10th postnatal day, phosphatidylethanolamine N-methyltransferase activity steadily increased 16-fold (p < 0.001). The results are in agreement with the hypothesis that the increase in phosphatidylcholine in rat liver during the perinatal period is due to an increased synthesis of CDPcholine, which is a consequence of the translocation of the cytidylyltransferase from cytosol to the endoplasmic reticulum.
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