FIGURE 1.

Schematic view of the DG in lipid metabolism and signal transduction. DGs in the endoplasmic reticulum (ER) include various species from distinct sources. 1,2-DG is derived from MG by MG acyltransferase and from phospholipase C-mediated PIP₂ breakdown. 1,3-DG and 2,3-DG are lipolytic products of TG by adipose TG lipase. These DGs are not intermingled and separately metabolized. Note that 1,2-DG serves not only as an intermediate product for TG synthesis, but also as a lipidic second messenger. It is phosphorylated by the action of DGK to produce phosphatidic acid (PA). DG, diacylglycerol; DGKε, DG kinase ε; MG, monoacylglycerol; PA, phosphatidic acid; PIP₂, phosphatidylinositol 4,5-bisphosphate; TG, triglyceride; 2-MG, 2-monoacylglycerol.