Enzymes for the Formation of Lecithins by Transmethylation in the Livers of Developing Rats 1

Summary

The activities of enzymes involved in the transmethylating pathway for the formation of lecithins (phosphatidyl choline) were determined in homogenates of the livers of rats at various stages of development. If the values are expressed per unit of protein weight, the enzyme synthesizing adenosylmethionine appears to be quite active at the end of the second week of fetal life. In contrast, values for the phospholipid methyltransferase, the enzyme catalyzing the stepwise methylation of a phospholipid (presumably phosphatidyl ethanolamine) to lecithin, remain quite low in the fetal livers, increase rapidly after birth, and reach their peak at about the eighth day of extrauterine life. This pattern is similar to that previously observed for choline phosphotransferase, the enzyme which catalyzes the final step in the cytidine-dependent pathway, except that the latter enzyme increases more markedly during the last week of fetal life, suggesting that this pathway reaches full development somewhat earlier than the transmethylating pathway.