Sprinz H, Schwinn J, Naumov S, Brede O
University of Leipzig, Research Unit Time-Resolved Spectroscopy, Permoserstrasse 15, D-04318, Leipzig, Germany.
Biochim Biophys Acta. 2000 Jan 3;1483(1):91-100. doi: 10.1016/s1388-1981(99)00175-4.
NMR spectroscopy and gas chromatography were used on methanolic solutions of fatty acid methyl esters and on small bilayer liposomes to study the radical-induced denaturation of the fatty acid residues from the natural cis-configuration into trans-isomers. To analyze the mechanism of the thiyl radical-catalyzed lipid isomerization, we compared the effects of thiols on oleic and linoleic fatty acid residues using pulse radiolysis, gamma-radiolysis and chemolysis (AAPH) to generate thiyl radicals. The isomerization step takes place within the adduct of the thiyl radical to an olefinic group of unsaturated fatty acids, but not within the pentadienyl radical. The stability of the adduct can be described by an equilibrium constant of (12+/-5) mol(-1) dm(3). The isomerization rate depends on the structure of the thiol. However, the resulting isomeric equilibrium (trans-fraction: 81%) does not depend on the structure of the thiyl radical or the organization of the lipids. Quantum chemical calculations were performed to estimate the barriers for rotation, the geometry and the enthalpy difference between cis- and trans-thiyl radical adducts.
核磁共振光谱法和气相色谱法被用于脂肪酸甲酯的甲醇溶液以及小双层脂质体，以研究自由基诱导脂肪酸残基从天然顺式构型转变为反式异构体的变性过程。为了分析硫自由基催化脂质异构化的机制，我们使用脉冲辐解、γ辐解和化学裂解（偶氮二异丁腈）产生硫自由基，比较了硫醇对油酸和亚油酸脂肪酸残基的影响。异构化步骤发生在硫自由基与不饱和脂肪酸的烯基加合物中，而不是在戊二烯基自由基中。加合物的稳定性可以用平衡常数(12±5) mol⁻¹ dm³来描述。异构化速率取决于硫醇的结构。然而，最终的异构平衡（反式分数：81%）并不取决于硫自由基的结构或脂质的组织形式。进行了量子化学计算，以估计顺式和反式硫自由基加合物之间的旋转势垒、几何结构和焓差。
