FIG 1.

Glycerophospholipid metabolism and prostaglandin E₂ biosynthesis. In the canonical PGE₂ biosynthetic pathway (light gray arrows), arachidonic acid is liberated directly from phospholipid membranes by cytosolic phospholipase A₂. Arachidonic acid can also be obtained via alternate lipid metabolism pathways (dark gray arrows) involving diacylglycerol. Lipid intermediates (dark gray rectangles) and the enzymes (light gray parallelograms) that catalyze each reaction are shown. Enzymes: cPLA₂, cytosolic phospholipase A₂; PLC, phospholipase C; PLD, phospholipase D; PAPs, phosphatidate phosphohydrolases; DAGL, diacylglycerol lipase; MAGL, monoacylglycerol lipase; COX-2, cyclooxygenase 2; mPGES1, microsomal prostaglandin E synthase 1.