title: Biosynthesis of a linoleic acid allylic epoxide: mechanistic comparison with its chemical synthesis and leukotriene A biosynthesis.
abstract: Biosynthesis of the leukotriene A (LTA) class of epoxide is a lipoxygenase-catalyzed transformation requiring a fatty acid hydroperoxide substrate containing at least three double bonds. Here, we report on biosynthesis of a dienoic analog of LTA epoxides via a different enzymatic mechanism. Beginning with homolytic cleavage of the hydroperoxide moiety, a catalase/peroxidase-related hemoprotein from Anabaena PCC 7120, which occurs in a fusion protein with a linoleic acid 9R-lipoxygenase, dehydrates 9R-hydroperoxylinoleate to a highly unstable epoxide. Using methods we developed for isolating extremely labile compounds, we prepared and purified the epoxide and characterized its structure as 9R,10R-epoxy-octadeca-11E,13E-dienoate. This epoxide hydrolyzes to stable 9,14-diols that were reported before in linoleate autoxidation (Hamberg, M. 1983. Autoxidation of linoleic acid: Isolation and structure of four dihydroxy octadecadienoic acids. Biochim. Biophys. Acta 752: 353-356) and in incubations with the Anabaena enzyme (Lang, I., C. Göbel, A. Porzel, I. Heilmann, and I. Feussner. 2008. A lipoxygenase with linoleate diol synthase activity from Nostoc sp. PCC 7120. Biochem. J. 410: 347-357). We also prepared an equivalent epoxide from 13S-hydroperoxylinoleate using a "biomimetic" chemical method originally described for LTA(4) synthesis and showed that like LTA(4), the C18.2 epoxide conjugates readily with glutathione, a potential metabolic fate in vivo. We compare and contrast the mechanisms of LTA-type allylic epoxide synthesis by lipoxygenase, catalase/peroxidase, and chemical transformations. These findings provide new insights into the reactions of linoleic acid hydroperoxides and extend the known range of catalytic activities of catalase-related hemoproteins.
authors.affiliation: Department of Pharmacology, Vanderbilt University, Nashville, TN 37232, USA.
authors.forename: Katrin
authors.initials: K
authors.lastname: Niisuke
authors.forename: William E
authors.initials: WE
authors.lastname: Boeglin
authors.forename: John J
authors.initials: JJ
authors.lastname: Murray
authors.forename: Claus
authors.initials: C
authors.lastname: Schneider
authors.forename: Alan R
authors.initials: AR
authors.lastname: Brash
mesh_terms: D017033:Anabaena / Q000737:chemistry / Q000201:enzymology* / Q000235:genetics; D001426:Bacterial Proteins / Q000235:genetics / Q000378:metabolism; D002374:Catalase / Q000235:genetics / Q000378:metabolism; D004852:Epoxy Compounds / Q000138:chemical synthesis / Q000737:chemistry / Q000378:metabolism; D005978:Glutathione / Q000378:metabolism; D017572:Leukotriene A4 / Q000096:biosynthesis*; D019787:Linoleic Acid / Q000096:biosynthesis / Q000138:chemical synthesis / Q000737:chemistry; D008084:Lipoxygenase / Q000235:genetics / Q000378:metabolism; D015394:Molecular Structure; D019906:Nuclear Magnetic Resonance, Biomolecular; D011993:Recombinant Fusion Proteins / Q000235:genetics / Q000378:metabolism
chemical_list: D001426:Bacterial Proteins; D004852:Epoxy Compounds; D017572:Leukotriene A4; D011993:Recombinant Fusion Proteins; D019787:Linoleic Acid; D002374:Catalase; D008084:Lipoxygenase; D005978:Glutathione