文章基本信息

标题：Biosynthesis of a linoleic acid allylic epoxide: mechanistic comparison with its chemical synthesis and leukotriene A biosynthesis
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作者：Katrin Niisuke ; William E. Boeglin ; John J. Murray 等
期刊名称：JLR Papers In Press
印刷版ISSN：0022-2275
电子版ISSN：1539-7262
出版年度：2009
卷号：50
期号：7
页码：1448-1455
DOI：10.1194/jlr.M900025-JLR200
语种：English
出版社：American Society for Biochemistry and Molecular Biology
摘要：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 9 R -lipoxygenase, dehydrates 9 R -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 9 R ,10 R -epoxy-octadeca-11 E ,13 E -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 13 S -hydroperoxylinoleate using a “biomimetic” chemical method originally described for LTA₄ synthesis and showed that like LTA₄, 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.