phosphatidylcholine
Summary
Most abundant membrane phospholipid and major component (~75%) of pulmonary surfactant, especially as dipalmitoylphosphatidylcholine (lecithin). Also a substrate for sphingomyelin synthesis and a marker of fetal lung maturity (L:S ratio).
Detail
Phosphatidylcholine is synthesized via the CDP-choline (Kennedy) pathway or by methylation of phosphatidylethanolamine using SAM (in liver). It is central to membrane fluidity, bile lipid solubilization, lipoprotein assembly, and surfactant function. In the lung, type II pneumocytes secrete lecithin-rich surfactant beginning around week 26 of gestation, increasing toward term; an amniotic fluid lecithin-to-sphingomyelin (L:S) ratio >2 predicts fetal lung maturity and low RDS risk. Choline deficiency contributes to fatty liver because hepatic VLDL export requires phosphatidylcholine. Lecithin-cholesterol acyltransferase (LCAT) uses phosphatidylcholine to esterify cholesterol in HDL maturation.
Sources
- First Aid for USMLE Step 1 2024
- Lippincott Biochemistry
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