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Leukotriene E4 was metabolized to two polar products by rat liver microsomes. These products were characterized by physico-chemical and chemical techniques. The chemical structures, (5S, 6R)-5,20-dihydroxy-6S-cysteinyl-7,9-trans-11,14-cis-icosatetraenoic acid (omega-hydroxy-leukotriene E4) and (5S, 6R)-5-hydroxy-6S-cysteinyl-7,9-trans-11,14-cis-icosatetraen-1,20-d ioic acid (omega-carboxy-leukotriene E4) suggested that leukotriene E4 was transformed by an omega-hydroxylase and omega-hydroxyleukotriene E dehydrogenase in sequence. N-Acetyl-leukotriene E4 was also transformed by these enzymes, but at a rate six times lower than leukotriene E4. The products formed from N-acetylleukotriene E4 were characterized as being N-acetyl-omega-hydroxy-leukotriene E4 and N-acetyl-omega-carboxy-leukotriene E4. Other substrates were 11-trans-leukotriene E4 and N-acetyl-11-trans-leukotriene E4. In contrast, leukotrienes C4 and D4 were not converted into omega-oxidized metabolites. The leukotriene E omega-hydroxylase reaction required NADPH and molecular oxygen as cofactors, and was most rapidly catalyzed by liver microsomes. Liver cytosol, fortified with NAD+, converted omega-hydroxyleukotriene E4 and N-acetyl-omega-hydroxy-leukotriene E4 into omega-carboxy metabolites. Microsomes contained at least 18 times less omega-hydroxy-leukotriene E dehydrogenase activity than did cytosol. Liver microsomes supplemented with acetyl-coenzyme A converted omega-hydroxy and omega-carboxy-leukotriene E4 into the corresponding N-acetyl derivatives. The novel enzyme, leukotriene E omega-hydroxylase, which is described here is distinct from a previously described leukotriene B omega-hydroxylase based on substrate competition and kinetic data.

Rat basophilic leukemia (RBL-1) cells incubated with ionophore A23187 and 5,8,11-eicosatrienoic acid produced three slow-reacting substances identified as leukotrienes C3, D3 and E3 by spectroscopic, chromatographic and enzymatic methods. 5,8,11,14,17-Eicosapentaenoic acid was similarly converted by RBL-1 cells to leukotrienes C5, D5. and E5. Leukotrienes C4, D4 and E4 were also formed in these experiments from endogenous arachidonic acid. Time-course studies, incubations with 3H-labeled leukotriene C3 and effects of acivicin [L-(alpha S, 5S)-alpha-amino-3-chloro-4,5-dihydro-5-isoxazoleacetic acid; a gamma-glutamyl transpeptidase inhibitor] indicated that leukotrienes C and D are intermediates in the formation of leukotrienes E. L-Cysteine enhanced the conversion of leukotriene C3 to leukotriene D3 and inhibited further degradation of leukotriene D3 to leukotriene E3.