Rate constants for peroxidation of polyunsaturated fatty acids and sterols in solution and in liposomes.
Rate constants for peroxidation of polyunsaturated fatty acids and sterols in solution and in liposomes.
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DOI：
10.1021/ja9029076
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发表时间：
2009-09-16
影响因子：
15
通讯作者：
Porter NA
中科院分区：
文献类型：
--
作者：
Xu L;Davis TA;Porter NA
用亚油酸自由基钟测定了几种不饱和脂质在37°C苯溶液和磷脂酰胆碱脂质体中的自氧化增殖速率常数。这种自由基时钟是基于由衍生自亚油酸的中间过氧自由基的氢原子提取（其导致反式、顺式共轭羟基十八碳二烯酸产物）和相同过氧自由基的β-断裂（其产生反式、反式产物羟基十八碳二烯酸）之间的竞争。通过这种方法在溶液中测定相对于亚油酸的速率常数（kp = 62 M− 1 s −1）为：花生四烯酸（kp = 197 ± 13 M− 1 s −1），二十碳五烯酸（kp = 249 ± 16 M− 1 s −1）、二十二碳六烯酸（kp = 334 ± 37 M− 1 s −1）、胆固醇（kp = 11 ± 2 M− 1 s −1）和7-脱氢胆固醇（kp = 2，260 ± 40 M− 1 s −1）。自由基氧化的多层和单层脂质体的各种混合物的甘油磷脂酰胆碱分子物种也进行了。在一些实验中，将胆固醇或7-脱氢胆固醇掺入经历氧化的脂质混合物中。在sn-2处带有亚油酸酯的磷脂酰胆碱是每个脂质体过氧化反应的组分，并且对于每个氧化反应，测定由该磷脂形成的反式、顺式/反式、反式（t，c/t，t）-共轭二烯氧化产物的比率。来自亚油酸酯的该t，c/t，t-产物比率用于“计时”脂质体组分作为脂质双层中的氢原子供体。应用该脂质双层自由基时钟，花生四烯酸（20：4）、二十碳五烯酸（20：5）、二十二碳六烯酸（22：6）和7-脱氢胆固醇的相对自氧化传播速率常数分别为115 ± 7、145 ± 8、172 ± 13和832 ± 86，反应趋势与溶液中的反应趋势平行。我们还从脂质体氧化中得出结论，亚油酸酯在十八碳链上不同位置（C-9和C-13）的过氧自由基具有不同的动力学性质。这与亚油酸酯的溶液氧化结果相反，在亚油酸酯的溶液氧化中，C-9和C-13过氧自由基具有相似的反应活性。我们认为过氧自由基的β-断裂依赖于溶剂的极性，而过氧自由基在脂质体氧化中的局部环境的极性取决于过氧自由基在十八碳链上的位置。
Rate constants for autoxidation propagation of several unsaturated lipids in benzene solution at 37°C and in phosphatidylcholine liposomes were determined by a linoleate radical clock. This radical clock is based on competition between hydrogen atom abstraction by an intermediate peroxyl radical derived from linoleic acid that leads to a trans,cis-conjugated hydroxyoctadecadienoic product and β–fragmentation of the same peroxyl that gives the trans,trans-product hydroxyoctadecadienoic acid. Rate constants determined by this approach in solution relative to linoleic acid (kp = 62 M−1s−1) were: arachidonic acid (kp = 197 ± 13 M−1s−1), eicosapentaenoic acid (kp = 249 ± 16 M−1s−1), docosahexaenoic acid (kp = 334 ± 37 M−1s−1), cholesterol (kp = 11 ± 2 M−1s−1), and 7-dehydrocholesterol (kp = 2,260 ± 40 M−1s−1). Free radical oxidations of multilamellar and unilamellar liposomes of various mixtures of glycerophosphatidylcholine molecular species were also carried out. In some experiments, cholesterol or 7-dehydrocholesterol was incorporated into the lipid mixture undergoing oxidation. A phosphatidylcholine bearing a linoleate ester at sn-2 was a component of each liposome peroxidation reaction and the ratio of trans,cis/trans,trans (t,c/t,t)-conjugated diene oxidation products formed from this phospholipid was determined for each oxidation reaction. This t,c/t,t-product ratio from linoleate was used to “clock” liposome constituents as hydrogen atom donors in the lipid bilayer. Application of this lipid bilayer radical clock gives relative autoxidation propagation rate constants of arachidonate (20:4), eicosapentaenoate (20:5), docosahexaenoate (22:6), and 7-dehydrocholesterol to be 115 ± 7, 145 ± 8, 172 ± 13, and 832 ± 86, respectively, a reactivity trend that parallels the one in solution. We also conclude from the liposome oxidations that linoleate peroxyl radicals at different positions on the eighteen-carbon chain (at C-9 and C-13) have different kinetic properties. This is in contrast to the results of solution oxidations of linoleate in which the C-9 and C-13 peroxyl radicals have similar reactivities. We suggest that peroxyl radical β–scission depends on solvent polarity and the polarity of the local environment of peroxyl radicals in liposomal oxidations depends on the position of the peroxyl radical on the eighteen-carbon chain.
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影响因子：
3.8
作者：
KAWAGISHI, H;KATSUMI, R;NAKAMURA, T
通讯作者：
NAKAMURA, T
影响因子：
1.9
作者：
COSGROVE, JP;CHURCH, DF;PRYOR, WA
通讯作者：
PRYOR, WA
影响因子：
4.1
作者：
Culbertson, SM;Antunes, F;Porter, NA
通讯作者：
Porter, NA
影响因子：
2.9
作者：
Akihisa, Toshihiro;Nakamura, Yuji;Kimura, Yumiko
通讯作者：
Kimura, Yumiko
影响因子：
1.1
作者：
BARCLAY, LRC;BASKIN, KA;LOCKE, SJ
通讯作者：
LOCKE, SJ