Aminopeptidase that preferentially cleaves tripeptides. Also has low epoxide hydrolase activity (in vitro). Can hydrolyze an epoxide moiety of LTA(4) to form LTB(4) (in vitro) (By similarity). H2O + leukotriene A4 = leukotriene B4 Binds 1 zinc ion per subunit. Lipid metabolism; leukotriene B4 biosynthesis. Belongs to the peptidase M1 family.