Isozymes of cyclooxygenase and lipoxygenase

具有生物活性的类二十烷酸，如花生四烯酸、血栓烷和白三烯，是由花生四烯酸产生的，花生四烯酸是各种脂氧合酶和环氧合酶的底物。我们研究了这些酶的催化特性和基因表达的调控机制，特别是参考他们的同工酶。1）5-脂氧合酶的选择性抑制剂：抗氧化剂YT-18引起的滞后期之前，5-脂氧合酶反应的启动。2）12-脂氧合酶的自杀性失活：白细胞12-脂氧合酶是一种典型的自杀性酶，它由花生四烯酸转化为14，15-环氧酸，产生15-过氧氢酸。几条证据表明，结合了14，15-环氧酸的酶失活。血小板12-脂氧合酶产生少量的15-过氧氢酸，几乎不被自杀灭活。3）白细胞12-脂氧合酶的底物花生四烯酸：花生四烯酸是大麻素受体的内源性配体。该化合物被白细胞12-脂氧合酶氧化，但是血小板酶的不良底物。12-脂氧合酶基因的转录调控：检测血小板12-脂氧合酶基因的启动子区，发现NFkB元件（-539至-530bp）被认为负调控该酶基因的转录。用TPA处理人巨核母细胞CMK细胞，TPA诱导环氧合酶-1酶。当小鼠成骨细胞MC 3 T3-E1细胞用TNF α处理时，环氧合酶-2被诱导。几行实验结果表明NF κ B和NF-IL 6在环氧合酶-2的转录中具有调节作用。

Bioactive eicosanoids such as prostaglandins, thromboxanes and leukotrienes are produced from arachidonic acid which is the substrate of various lipoxygenases and cyclooxygenases. We studied the catalytic properties and the regulatory mechanism of gene expression of these enzymes with special reference to their isozymes.1)Selective inhibitor of 5-lipoxygenase : An antioxidant YT-18 caused a lag phase prior to initiation of 5-lipoxygenase reaction. This effect was specific for 5-lipoxygenase.2)Suicide inactivation of 12-lipoxygenase : Leukocyte 12-lipoxygenase is a typical suicide enzyme.The enzymeproduced 15-hydroperoxy acid as a minor product from arachidonic acid, which was further transformed to 14,15-epoxy acid by the same enzyme. Several lines of evidence suggested the inactivation of the enzyme which incorporated the 14,15-epoxy acid. Platelet 12-lipoxygenase produced little amount of 15-hydroperoxy acid and was scarcely suicide-inactivated.3)Anandamide as substrate of leukocyte 12-lipoxygenase : Anandamide(arachidonylethanolamine)is an endogenous ligand of cannabinoid receptor. The compound was oxygenated by leukocyte 12-lipoxygenase, but was a poor substrate of platelet enzyme. The 12-oxygenated anandamide was biologically almost inactive.Transcriptional regulation of 12-lipoxygenase gene : The promoter region of platelet 12-lipoxygenase gene was examined, and NFkB element(-539 to -530bp)was proposed to negatively regulate the transcription of the enzyme gene.Induction of cyclooxygenase-1 : Human megakaryoblastic CMK cells were treated wtih TPA,which induced cyclooxygenase-1 enzyme.Transcriptional regulation of cyclooxygenase-2 : When murine osteoblastic MC3T3-E1 cells were treated with TNFalpha, cyclooxygenase-2 was induced. Several lines of experimented findings suggested a regulatory role of NFkB and NF-IL6 in the transcription of cyclooxygenase-2.