Phosphatidic acid (PA) is the simplest natural glycerophospholipid in living organisms consisting of glycerol, an acyl chain, and a phosphate. As a minor component in biological membranes (about 1-4% of membrane lipids), PA is still involved in multiple intracellular processes. For example, PA is an intermediate for other phospholipids, acts as a lipid second messenger, and is also a modulator of physicochemical properties of the membrane. The related lipid lysophosphatidic acid (LPA) has only one acyl chain and carries a more negative charge than PA does when present in a phosphatidylcholine bilayer. Influenced by the ratio of the headgroup to the tail, PA is a cone-shaped lipid that tends to form monolayers spontaneously bulge towards the tail of hydrocarbons with an aqueous core surrounded by the hydrophilic headgroups. Whereas LPA is modeled as an inverted cone, which tends to form spherical micelles with headgroups surrounding the hydrophobic tails directed inward.
