Distinction of Phosphatidylcholine Synthesis between CDP-Choline and PEMT pathways

This paper is quite interesting and could be eye-opening for some.

“The molecular diversity of PC and other phospholipids is dictated by the combination of different lengths, number of double bonds, and types of linkages of hydrocarbon chains. As a result, a single mammalian cell contains at least a thousand species of phospholipids.

In most mammalian cells, PC is synthesized mainly via the CDP-choline pathway.

This pathway uses choline as an initial substrate and is catalyzed by three enzymes: choline kinase, CTP:phosphocholine cytidylyltransferase (CT), and cholinephosphate transferase, with CT as the rate-limiting enzyme.

Hepatocytes are unique because they also possess a high activity of phosphatidylethanolamine methyltransferase (PEMT) that converts PE to PC via three sequential steps of methylation in addition to a high level of CDP-choline pathway activity.

The PEMT pathway seems redundant because its product, PC, is also synthesized by the CDP-choline pathway in hepatocytes. Therefore, the PEMT pathway is traditionally considered a backup pathway for PC synthesis in hepatocytes.

However, recent studies indicate that these two pathways apparently have opposite effects on proliferative characteristics of the liver and liver-derived cell lines. These studies suggest that the higher activity of the CDP-choline pathway favours the faster proliferation of hepatocytes.”