Leukotriene A4 is a leukotriene.Leukotriene A4 hydrolase converts it to Leukotriene B4.(2s-(2 alpha,3 beta(1e,3e,5z,8z)))-3-(1,3,5,8-tetradecatetraenyl)oxiranebutanoic acid. An unstable allylic epoxide, formed from the immediate precursor 5-hpete via the stereospecific removal of a proton at c-10 and dehydration. 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.1,2 LTA4 is rapidly metabolized by LTA4 hydrolase or LTC4 synthase to LTB4 or LTC4, respectively.2 LTA4, from leukocytes, is known to undergo transcellular metabolism in platelets, erythrocytes, and endothelial cells.3 Further metabolism of LTA4 by 15-LO leads to lipoxin biosynthesis.2 LTA4 as a free acid is highly unstable. The methyl ester is stable and can be readily hydrolyzed to the free acid as needed.