The CDP-choline route: choline is phosphorylated, activated with CTP and transferred to diacylglycerol
Route: Choline → Phosphocholine → CDP-choline + 1,2-Dipalmitoyl-sn-glycerol (diacylglycerol) → 1,2-Dipalmitoyl-sn-glycero-3-phosphocholine (phosphatidylcholine)
Phosphatidylcholine is the most common phospholipid in mammals. Dietary choline is activated in a series of reactions like those for ethanolamine. Choline kinase uses ATP to make phosphocholine. CTP:phosphocholine cytidylyltransferase (CCT) joins phosphocholine to CTP and releases pyrophosphate, which gives CDP-choline. This is the rate-limiting step of the pathway. CCT is amphitropic: a part of the enzyme inserts into the membrane when the phosphatidylcholine level falls, and this activates it. The enzyme card shows the catalytic domain only. Last, a phosphotransferase moves the phosphocholine unit of CDP-choline onto a hydroxyl group of a diacylglycerol and releases CMP. Two related enzymes can do this step: choline phosphotransferase 1 (CHPT1), which makes only phosphatidylcholine and is shown here, and choline/ethanolamine phosphotransferase 1 (CEPT1), which makes both phosphatidylcholine and phosphatidylethanolamine. The drawings show palmitoyl on both acyl positions as a stand-in. The liver has a second route that makes phosphatidylcholine from phosphatidylethanolamine by three methylations with S-adenosylmethionine as the methyl donor, when dietary choline is insufficient; it is not drawn here.
Practice this pathway All pathways
| Step | Enzyme | EC | In | Out |
|---|---|---|---|---|
| 1 | Choline kinase alpha | 2.7.1.32 | ATP | ADP |
| 2 | CTP:phosphocholine cytidylyltransferase | 2.7.7.15 | CTP | PPᵢ |
| 3 | Choline phosphotransferase 1 | 2.7.8.2 | CMP |
Build any of these from its atoms.
Enzyme names and EC numbers are those used on the interactive board. Checked against sources: see the claim table in the repository (tools/pathway_data/checks).