title: Hepoxilin A3 synthase.
abstract: Hepoxilins constitute a group of 12S-hydroperoxyeicosatetraenoic acid (12S-HpETE)-derived epoxy-hydroxy fatty acids that have been detected in various cell types and tissues. Although hepoxilin A3 (HXA3) exhibits a myriad of biological activities, its biosynthetic mechanism was not investigated in detail. Here we review the isolation, cloning, and characterization of a leukocyte-type 12S-lipoxygenase (12S-LOX) from rat insulinoma cells RINm5F, which exhibits an intrinsic hepoxilin A3 synthase activity. Confirmation for this observation was achieved by coimmunoprecipitation of HXA3 synthase activity with an anti-leukocyte 12S-LOX antibody, preparation of recombinant rat 12S-LOX enzyme from RINm5F cells, and assay of HXA3 synthase activity therein. Site-directed mutagenesis studies performed on rat 12S-LOX showed that 12-lipoxygenating enzyme species exhibit a strong HXA3 synthase activity that is impaired when the positional specificity of arachidonic acid is altered in favor of 15-lipoxygenation. Inasmuch as cellular glutathione peroxidases (cGPx and PHGPx) and HXA3 synthase compete for the same substrate 12S-HpETE, it can be proposed that the overall activity of glutathione peroxidases, representing the overall peroxide tone, finely tunes the rate of HXA3 formation.
authors.affiliation: Eicosanoid and Lipid Research Division, Centre of Experimental Gynecology and Breast Research, University Medical Centre Berlin, Charité-Campus Benjamin Franklin, D-12200 Berlin, Germany. nigam@zedat.fu-berlin.de
authors.forename: Santosh
authors.initials: S
authors.lastname: Nigam
authors.forename: Maria-Patapia
authors.initials: MP
authors.lastname: Zafiriou
mesh_terms: D015126:8,11,14-Eicosatrienoic Acid / Q000031:analogs & derivatives* / Q000378:metabolism; D000595:Amino Acid Sequence; D000818:Animals; D001092:Arachidonate 12-Lipoxygenase / Q000737:chemistry* / Q000235:genetics / Q000378:metabolism; D001093:Arachidonate 15-Lipoxygenase / Q000737:chemistry / Q000378:metabolism; D045744:Cell Line, Tumor; D019746:Intramolecular Oxidoreductases / Q000037:antagonists & inhibitors / Q000737:chemistry* / Q000235:genetics / Q000378:metabolism; D016859:Lipoxygenase Inhibitors; D008969:Molecular Sequence Data; D009363:Neoplasm Proteins / Q000037:antagonists & inhibitors / Q000737:chemistry / Q000235:genetics / Q000378:metabolism; D051381:Rats; D016415:Sequence Alignment
chemical_list: D016859:Lipoxygenase Inhibitors; D009363:Neoplasm Proteins; C038243:8-hydroxy-11,12-epoxyeicosa-5,9,14-trienoic acid; D001092:Arachidonate 12-Lipoxygenase; D001093:Arachidonate 15-Lipoxygenase; D019746:Intramolecular Oxidoreductases; C473385:hepoxilin synthase; D015126:8,11,14-Eicosatrienoic Acid