Phosphatidylcholine

Phosphatidylcholine, also known as lecithin, is a glycerophospholipid and one of the most abundant phospholipids in eukaryotic cell membranes. It consists of a glycerol backbone bearing two fatty acyl chains at the sn-1 and sn-2 positions and a phosphocholine headgroup at the sn-3 position. The fatty acid composition varies, giving rise to many species such as 16:0/18:1 or 18:0/18:1, while the headgroup remains phosphocholine. At physiological pH, the molecule is zwitterionic.

Phosphatidylcholine is a major component of cellular membranes and lipoproteins. In the lung, a specialized form called dipalmitoylphosphatidylcholine is a key constituent of alveolar surfactant, reducing surface tension to stabilize the air–lung interface. Dietary sources include soy and egg lecithin, and phosphatidylcholine serves as a reservoir of the essential nutrient choline.

Biosynthesis occurs mainly via the Kennedy pathway, or CDP-choline pathway. In this route, choline is phosphorylated to phosphocholine, converted to CDP-choline, and then diacylglycerol is added to form phosphatidylcholine. An alternative route is the phosphatidylethanolamine N-methyltransferase (PEMT) pathway, where phosphatidylethanolamine is methylated to produce phosphatidylcholine.

Functions extend beyond membrane structure. PC participates in membrane trafficking and lipoprotein assembly, notably very low-density lipoprotein (VLDL) formation. As a source of choline, it influences acetylcholine synthesis and one-carbon metabolism, with physiological importance in liver and neural tissues.

Industrial and research relevance: Lecithin is widely used as an emulsifier in food and cosmetics. In lipidomics, PC species are analyzed to study membrane composition and metabolic states.