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Leukotriene A₄ (LTA₄) is synthesized in mast cells, eosinophils, and neutrophils from arachidonic acid by 5-lipoxygenase (5-LO), which exhibits both lipoxygenase and LTA₄ synthase activities. LTA₄ is rapidly metabolized by LTA₄ hydrolase or LTC₄ synthase to LTB₄ or LTC₄, respectively. LTA₄, from leukocytes, is known to undergo transcellular metabolism in platelets, erythrocytes, and endothelial cells. Further metabolism of LTA₄ by 15-LO leads to lipoxin biosynthesis. LTA₄ as a free acid is highly unstable. The methyl ester is stable and can be readily hydrolyzed to the free acid as needed.

LTA4 (Leukotriene A4 methyl ester) is an unstable intermediate in the biosynthesis of LTB4 and LTC4.

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