Omega-oxidation of cysteine-containing leukotrienes by rat-liver microsomes. Isolation and characterization of omega-hydroxy and omega-carboxy metabolites of leukotriene E4 and N-acetylleukotriene E4.
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.
Orning
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Department of Physiological Chemistry, Karolinska Institutet, Stockholm, Sweden.
D000123:Acetyltransferases / Q000378:metabolism; D000429:Alcohol Oxidoreductases / Q000378:metabolism; D000818:Animals; D003577:Cytochrome P-450 Enzyme System; D000072470:Cytochrome P450 Family 4; D003600:Cytosol / Q000201:enzymology; D007668:Kidney / Q000201:enzymology; D007700:Kinetics; D017999:Leukotriene E4 / Q000031:analogs & derivatives; D008099:Liver / Q000201:enzymology; D008168:Lung / Q000201:enzymology; D008297:Male; D013058:Mass Spectrometry; D008861:Microsomes / Q000201:enzymology; D008862:Microsomes, Liver / Q000201:enzymology*; D006899:Mixed Function Oxygenases / Q000378:metabolism; D009928:Organ Specificity; D010084:Oxidation-Reduction; D051381:Rats; D011919:Rats, Inbred Strains; D013189:SRS-A / Q000031:analogs & derivatives* / Q000302:isolation & purification / Q000378:metabolism*
D013189:SRS-A; D017999:Leukotriene E4; C047630:N-acetylleukotriene E4; D003577:Cytochrome P-450 Enzyme System; D006899:Mixed Function Oxygenases; D000429:Alcohol Oxidoreductases; C054534:omega-hydroxyleukotriene E4 dehydrogenase; D000072470:Cytochrome P450 Family 4; C040780:leukotriene B4 20-hydroxylase; D000123:Acetyltransferases