Trudell J R, Gut J
Department of Anesthesia, Stanford University, School of Medicine, CA 94305-5117.
Free Radic Biol Med. 1989;7(3):275-84. doi: 10.1016/0891-5849(89)90135-4.
Rat hepatocyte homogenates convert 5-hydroperoxyeicosatetraenoic acid (5-HPETE) into biologically active leukotriene B4 (LTB4) as well as less active all-trans-LTB4 (i.e., 6-trans-LTB4 and 6-trans-12-epi-LTB4). Here, we present a hypothesis of the reaction mechanism and the minimal structural requirements of the active enzyme based on the following experimental evidence: The ED50 of the inhibitors 5,8,11,14-eicosatetraynoic acid (ETYA) and 5,6-dehydro-eicosatetraenoic acid was approximately 100-fold higher than for 5-lipoxygenase. Propanethiol and O2 were strong inhibitors of LTB4 formation, whereas butylated hydroxytoluene, nordihydroguaiaretic acid, metyrapone, Desferal and CO had no effect. Cytochrome c, catalase, hematin, and a Fe3+/Fe2+ couple, but not iron-free protoporphyrin IX, catalyzed the formation of only all-trans-LTB4. LTB4 formation in hepatocyte homogenates was heat- and trypsin-sensitive whereas all-trans-LTB4 formation was not. We propose that a ferric heme iron forms a ferryl-hydroxo complex upon homolytic scission of the oxygen-oxygen bond in 5-HPETE and the resulting 5,6-trans-epoxide radical is oxidized by the ferryl-hydroxo complex to yield LTA4. A mechanism for hydrolysis of LTA4 is described that results in formation of LTB4 (less than 1% yield) rather than all-trans-LTB4.
大鼠肝细胞匀浆可将5-氢过氧化二十碳四烯酸（5-HPETE）转化为具有生物活性的白三烯B4（LTB4）以及活性较低的全反式白三烯B4（即6-反式白三烯B4和6-反式-12-表白三烯B4）。在此，我们基于以下实验证据提出了反应机制和活性酶的最小结构要求的假设：抑制剂5,8,11,14-二十碳四炔酸（ETYA）和5,6-脱氢二十碳四烯酸的半数有效剂量（ED50）比5-脂氧合酶的约高100倍。丙硫醇和O2是LTB4形成的强抑制剂，而丁基羟基甲苯、去甲二氢愈创木酸、甲吡酮、去铁胺和CO则无作用。细胞色素c、过氧化氢酶、血红素和Fe3+/Fe2+偶联物，而非无铁原卟啉IX，仅催化全反式白三烯B4的形成。肝细胞匀浆中LTB4的形成对热和胰蛋白酶敏感，而全反式白三烯B4的形成则不然。我们提出，三价血红素铁在5-HPETE中氧-氧键均裂时形成铁氧-羟基复合物，生成的5,6-反式环氧自由基被铁氧-羟基复合物氧化生成白三烯A4（LTA4）。描述了一种LTA4水解的机制，该机制导致形成LTB4（产率低于1%）而非全反式白三烯B4。
