Phosphatides

Phosphatides are a class of phospholipids that form a major component of biological membranes. They are glycerophospholipids built on a glycerol backbone with two fatty acid chains esterified at the sn-1 and sn-2 positions and a phosphate-containing head group attached to the third hydroxyl. The head group varies and includes choline, ethanolamine, serine, or inositol, yielding phosphatidylcholine, phosphatidylethanolamine, phosphatidylserine, and phosphatidylinositol, among others. Cardiolipin is a distinctive phosphatide found in mitochondrial membranes.

Phosphatides are amphipathic and readily form lipid bilayers, micelles, and liposomes. They are synthesized mainly in the endoplasmic reticulum and mitochondria via pathways that assemble the glycerol backbone and then attach a head group using CDP-activated donors (for example, CDP-choline to make phosphatidylcholine, CDP-ethanolamine for phosphatidylethanolamine). Phosphatidylserine and phosphatidylinositol are produced by head-group exchange or sequential acylation and phosphorylation steps. These lipids can be modified by acyl chain remodeling and are degraded by phospholipases.

In biology, phosphatides support membrane structure and dynamics, participate in signaling (notably phosphatidylinositol phosphates), and provide precursors for bioactive molecules. They also play roles in blood coagulation and apoptosis when externalized on the cell surface. In industry, phosphatidylcholine-rich lecithin is used as an emulsifier, and phospholipids are employed to form liposomes for research and drug delivery. Abnormal phospholipid antibodies are associated with antiphospholipid syndrome.