Leukotriene A<sub>4</sub> (LTA<sub>4</sub>) is a leukotriene, and is the precursor for the productions of leukotriene B<sub>4</sub> (LTB<sub>4</sub>) and leukotriene C<sub>4</sub> (LTC<sub>4</sub>).
Following the biosynthesis of eicosanoid, triggered as a result of infection or inflammation, the resulting arachidonic acid substrate is released from the cell membrane phospholipid will enter the lipooxygenase pathway to produce leukotriene A<sub>4</sub>. In this pathway, arachidonic acid is converted into 5-hydroperoxyeicosatetraenoic acid (5-HPETE) as a result of a catalytic complex consisting of the enzyme 5-lipoxygenase (5-LO) and 5-lipoxygenase-activating protein (FLAP) in the presence of ATP and calcium ions. The resulting 5-HPETE yields the unstable allylic epoxide substrate LTA<sub>4</sub> which is quickly hydrolyzed by the leukotriene A4 hydrolase (LTA<sub>4</sub>H) enzyme to produce LTB<sub>4</sub>, or synthesized by leukotriene C4 synthase (LTC<sub>4</sub>S) with the addition of glutathione to produce LTC<sub>4</sub> which can be further metabolized to produce leukotriene D<sub>4</sub> (LTD<sub>4</sub>) and leukotriene E<sub>4</sub> (LTE<sub>4</sub>). The lipooxygenase pathway is one of several possible pathways including the cyclooxygenase pathway (also PGH synthase pathway), isoprostane pathway, and cytochrome P450 epoxygenases pathway following the arachidonic acid metabolism, but is the only pathway in which the subsequent steps will lead to the production of leukotrienes.