Garcia M C, Sprecher H, Rosenthal M D
Department of Biochemistry, Eastern Virginia Medical School, Norfolk 23501.
Lipids. 1990 Apr;25(4):211-5. doi: 10.1007/BF02535749.
This study has utilized radiolabeled analogues of arachidonic acid to study the substrate specificity of elongation of long-chain polyunsaturated fatty acids. Human umbilical vein endothelial cells were incubated for 2-72 hr in medium supplemented with 0.9-2.6 microM [14C]fatty acid, and cellular glycerolipids were analyzed by gas-liquid chromatography with radioactivity detection. Elongation of naturally occurring C20 polyunsaturated fatty acids occurred with eicosapentaenoate (20:5(n-3] greater than Mead acid (20:3(n-9] greater than arachidonate (20:4(n-6]. Chain length markedly influenced the extent of elongation of 5,8,11,14-tetraenoates (18:4 greater than 19:4 greater than 20:4 greater than 21:4); effects of initial double bond position were also observed (6,9,12,15-20:4 greater than 4,7,10,13-20:4. Neither 5,8,14- nor 5,11,14-20:3 was elongated to the extent of 5,8,11-20:3. Differences between polyunsaturated fatty acids were observed both in the initial rates and in the maximal percentages of elongation, suggesting that the content of cellular C20 and C22 fatty acids may represent a balance between chain elongation and retroconversion. Umbilical vein endothelial cells do not exhibit significant desaturation of either 22:4(n-6) or 22:5(n-3). By contrast, incubation with 5,8,11,14-[14C]18:4(n-4) resulted in formation of both [14C]20:5(n-4) and [14C]22:5(n-4). The respective time courses for the appearances of [14C]22:5(n-4) and [14C]20:5(n-5) suggests delta 6 desaturation of [14C]22:4(n-4) rather than delta 4 desaturation of [14C]20:4(n-4).
本研究利用花生四烯酸的放射性标记类似物来研究长链多不饱和脂肪酸延长的底物特异性。将人脐静脉内皮细胞在补充有0.9 - 2.6微摩尔[14C]脂肪酸的培养基中孵育2 - 72小时，并用放射性检测的气液色谱法分析细胞甘油脂质。天然存在的C20多不饱和脂肪酸的延长情况为：二十碳五烯酸（20:5(n - 3)）大于米德酸（20:3(n - 9)）大于花生四烯酸（20:4(n - 6)）。链长对5,8,11,14 - 四烯酸（18:4大于19:4大于20:4大于21:4）的延长程度有显著影响；也观察到了初始双键位置的影响（6,9,12,15 - 20:4大于4,7,10,13 - 20:4）。5,8,14 - 20:3和5,11,14 - 20:3的延长程度均不及5,8,11 - 20:3。在初始速率和最大延长百分比方面均观察到多不饱和脂肪酸之间的差异，这表明细胞C20和C22脂肪酸的含量可能代表链延长和逆向转化之间的平衡。脐静脉内皮细胞对22:4(n - 6)或22:5(n - 3)均未表现出明显的去饱和作用。相比之下，用5,8,11,14 - [14C]18:4(n - 4)孵育导致形成了[14C]20:5(n - 4)和[14C]22:5(n - 4)。[14C]22:5(n - 4)和[14C]20:5(n - 5)出现的各自时间进程表明是[14C]22:4(n - 4)的δ6去饱和而不是[14C]20:4(n - 4)的δ4去饱和。
