出版社：American Society for Biochemistry and Molecular Biology
摘要：Leukotriene (LT)A4 and closely related allylic epoxides are pivotal intermediates in lipoxygenase (LOX) pathways to bioactive lipid mediators that include the leukotrienes, lipoxins, eoxins, resolvins, and protectins. Although the structure and stereochemistry of the 5-LOX product LTA4 is established through comparison to synthetic standards, this is the exception, and none of these highly unstable epoxides has been analyzed in detail from enzymatic synthesis. Understanding of the mechanistic basis of the cis or trans epoxide configuration is also limited. To address these issues, we developed methods involving biphasic reaction conditions for the LOX-catalyzed synthesis of LTA epoxides in quantities sufficient for NMR analysis. As proof of concept, human 15-LOX-1 was shown to convert 15 S -hydroperoxy-eicosatetraenoic acid (15 S -HPETE) to the LTA analog 14 S ,15 S - trans -epoxy-eicosa-5 Z ,8 Z ,10 E ,12 E -tetraenoate, confirming the proposed structure of eoxin A4. Using this methodology we then showed that recombinant Arabidopsis AtLOX1, an arachidonate 5-LOX, converts 5 S -HPETE to the trans epoxide LTA4 and converts 5 R -HPETE to the cis epoxide 5- epi -LTA4, establishing substrate chirality as a determinant of the cis or trans epoxide configuration. The results are reconciled with a mechanism based on a dual role of the LOX nonheme iron in LTA epoxide biosynthesis, providing a rational basis for understanding the stereochemistry of LTA epoxide intermediates in LOX-catalyzed transformations.
关键词：5-lipoxygenase ; 15-lipoxygenase ; hydroperoxy-eicosatetraenoic acid ; nuclear magnetic resonance
