Figure 2.

Arachidonic acid (AA) is liberated from the plasma membrane via phospholipase A2 (PLA₂). AA can be recycled by the Lands cycle, which is a reacylation/deacylation cycle, that serves to keep the concentration of free AA at a low level. AA is converted by different lipoxygenase enzymes to form either hydroperoxyeicosatetraenoic acid (HPETEs) which is then reduced to the corresponding hydroxy compound. 12-HETE can signal through the G-protein-coupled receptor 12-HETE (12-HETER). 8-HETE, 15-HETE and leukotriene LTB₄ can signal through PPAR. 5-LOX and 5-lipoxygenase activating protein (FLAP) convert AA to leukotrienes through a series of reactions using 5-LOX and as well as LTA₄ hydrolase and LTC₄ synthase including LTA₄, LTB₄, LTC₄, LTD₄, and LTE₄. LTB₄ is exported via multidrug resistance protein 4 (MRP4) to signal through leukotriene B4 receptor BLT1/2. LTC₄ and LTD₄ is exported via multidrug resistance protein 1 (MRP1) to bind to cysteinyl leukotriene receptor 1 or 2 (CysLTR1/2).