Diacylglycerol

Diacylglycerol (DAG) is a glyceride composed of glycerol with two fatty acyl substituents esterified to the first and second hydroxyl groups, leaving the third hydroxyl free. In biochemistry, DAG is primarily known as an intermediate in lipid metabolism and as a second messenger in cellular signaling. The most common structural form is 1,2-DAG, though 1,3-DAG is also possible depending on the positions of the fatty acids.

Biosynthesis and interconversion: DAG is produced during triglyceride synthesis when phosphatidic acid is dephosphorylated by phosphatidic acid phosphatase to yield DAG, which can then be acylated to form triglycerides. DAG also arises from hydrolysis of phospholipids by phospholipase C, which cleaves phosphatidylinositol 4,5-bisphosphate to produce IP3 and DAG. In the breakdown of stored fats, lipases can generate DAG as an intermediate. DAG can be phosphorylated by diacylglycerol kinases to form phosphatidic acid, linking signaling to phospholipid and lipid biosynthesis pathways.

Functions: In signaling, DAG acts as a second messenger by activating conventional and novel protein kinase C (PKC) isoforms at membranes rich in DAG, initiating phosphorylation cascades that regulate proliferation, differentiation, and metabolism. DAG may therefore couple receptor activation to downstream signaling and membrane trafficking. In metabolism, DAG serves as an intermediate that connects glycerolipid synthesis with phospholipid formation and energy storage.

Occurrence and applications: DAG is present in cellular membranes at low abundance and increases transiently in response to receptor signaling. Dietarily, diacylglycerol is also found in certain edible fats and DAG-enriched oils used as functional lipids with distinct metabolic effects.