O'Leary V J, Graham A, Stone D, Darley-Usmar V M
Enzymology Group, Biology Divison, Wellcome Research Laboratories, Beckenham, Kent, UK.
Free Radic Biol Med. 1996;20(4):525-32. doi: 10.1016/0891-5849(95)02084-5.
The enzyme 15-lipoxygenase has been implicated in the oxidation of low-density lipoprotein (LDL) in human atherosclerotic lesions. The biochemical mechanism for this oxidative process is not fully understood, and the interaction of the lipoxygenase-modified lipoprotein with metals or metalloproteins has not been explored. In the present study we have used soybean lipoxygenase to model the interaction of the enzyme with LDL and show that a direct oxygenation of fatty acids occurs, including those esterified to cholesterol, with no lag phase or change in electrophoretic mobility of the LDL particle but with some depletion of alpha-tocopherol. The enzyme-dependent oxidation may involve propagation through the release of peroxyl radicals from its active site but appears to have no requirement for free iron or copper. When lipoxygenase-treated LDL is exposed to either copper (II) or metMb, a rapid oxidation process occurs, resulting in a marked decrease in resistance to oxidation and an increase in the rate of modification to a form with increased electrophoretic mobility. This effect was not seen if lipoxygenase-treated LDL was oxidized by SIN-1, a peroxynitrite donor that oxidizes LDL with no requirement for endogenous lipid hydroperoxides. We propose that a synergistic interaction may occur between the peroxides inserted into LDL as a consequence of the enzymatic action of lipoxygenase with haem proteins or copper, which decreases the potency of the endogenous antioxidants and enhances oxidation.
15-脂氧合酶已被认为与人类动脉粥样硬化病变中低密度脂蛋白（LDL）的氧化有关。这种氧化过程的生化机制尚未完全了解，脂氧合酶修饰的脂蛋白与金属或金属蛋白的相互作用也未得到探索。在本研究中，我们使用大豆脂氧合酶来模拟该酶与LDL的相互作用，并表明脂肪酸发生了直接氧化，包括那些酯化到胆固醇上的脂肪酸，LDL颗粒的电泳迁移率没有延迟期或变化，但α-生育酚有一些消耗。酶依赖性氧化可能涉及通过从其活性位点释放过氧自由基进行传播，但似乎不需要游离铁或铜。当用脂氧合酶处理的LDL暴露于铜（II）或高铁肌红蛋白时，会发生快速氧化过程，导致抗氧化性显著降低，并且修饰速率增加，形成电泳迁移率增加的形式。如果用SIN-1（一种过氧亚硝酸盐供体，其氧化LDL不需要内源性脂质氢过氧化物）氧化用脂氧合酶处理的LDL，则不会看到这种效果。我们提出，由于脂氧合酶与血红素蛋白或铜的酶促作用，插入LDL中的过氧化物之间可能会发生协同相互作用，这会降低内源性抗氧化剂的效力并增强氧化作用。
