phosphatidic

Phosphatidic, usually encountered as phosphatidic acid (PA), is a glycerophospholipid that also serves as a fundamental metabolic intermediate and signaling lipid. It consists of a glycerol backbone with two fatty acyl chains at the sn-1 and sn-2 positions and a phosphate-containing head group at the sn-3 position. The phosphate head is negatively charged, giving PA distinctive amphipathic properties and a propensity to associate with membranes.

Biosynthesis and metabolism: PA is produced when glycerol-3-phosphate is acylated to form lysophosphatidic acid and then PA by the addition of a second acyl chain. It can also be generated by phospholipase D hydrolysis of phosphatidylcholine or phosphatidylethanolamine, or by phosphorylation of diacylglycerol. In cells, PA is a central intermediate in the CDP-diacylglycerol pathway for the synthesis of major phospholipids, and it can be dephosphorylated to diacylglycerol by lipid phosphate phosphatases.

Function: PA serves as a substrate for further lipid synthesis, including CDP-diacylglycerol formation and the production of phosphatidylglycerol, phosphatidylinositol, and cardiolipin. It is also a signaling lipid that can recruit proteins to membranes, influence membrane curvature, and participate in pathways regulating vesicle trafficking, cytoskeletal dynamics, and autophagy.

Distribution and significance: PA is present across all domains of life, with acyl chain composition reflecting organism and tissue type. In eukaryotic cells, localized PA production at membranes provides spatial regulation of signaling and membrane biogenesis, linking lipid metabolism to cellular function.

Notes: The term phosphatidic is typically shorthand for phosphatidic acid; sources may use PA or phosphatidate. As such, PA is a key lipid both as a structural component and as a versatile metabolite.