The same rat Delta6-desaturase not only acts on 18- but also on 24-carbon fatty acids in very-long-chain polyunsaturated fatty acid biosynthesis.
The same rat Delta6-desaturase not only acts on 18- but also on 24-carbon fatty acids in very-long-chain polyunsaturated fatty acid biosynthesis.
复制标题
在超长链多不饱和脂肪酸生物合成中，相同的大鼠 Delta6-去饱和酶不仅作用于 18 碳脂肪酸，还作用于 24 碳脂肪酸。
作者：
S. d’Andrea;H. Guillou;S. Jan;D. Catheline;J. Thibault;M. Bouriel;V. Rioux;P. Legrand
最近克隆的 Delta6 去饱和酶已知可催化超长链多不饱和脂肪酸生物合成的第一步，即亚油酸和 α-亚麻酸的去饱和。该酶还可以催化末端去饱和步骤，即 24 碳高度不饱和脂肪酸的去饱和，这一假设从未得到阐明。为了检验这一假设，研究了 COS-7 细胞中表达的大鼠 Delta6-去饱和酶的活性。通过蛋白质印迹分析重组 Delta6-去饱和酶表达，显示 45 kDa 处的单条带。通过将转染细胞与 C(22:5) n-3 一起孵育来测量该酶在 C(24:5) n-3 到 C(24:6) n-3 的 Delta6 去饱和过程中的推定参与。尽管转染和未转染的 COS-7 细胞都能够通过 C(22:5) n-3 的延伸来合成 C(24:5) n-3，但只有表达 Delta6-去饱和酶的细胞也能够产生 C(24:6) n-3。此外，在表达或不表达 Delta6-去饱和酶的 COS-7 细胞的匀浆中体外测定了 [1-(14)C]C(24:5) n-3 的 Delta6-去饱和作用，表明 Delta6-去饱和酶催化 C(24:5) n-3 向 C(24:6) n-3 的转化。因此，有证据表明，同一大鼠Delta6-去饱和酶不仅催化C(18:3) n-3向C(18:4) n-3的转化，而且还催化C(24:5) n-3向C(24:6) n-3的转化。强烈建议在 n-6 系列中采用类似的机制。
The recently cloned Delta6-desaturase is known to catalyse the first step in very-long-chain polyunsaturated fatty acid biosynthesis, i.e. the desaturation of linoleic and alpha-linolenic acids. The hypothesis that this enzyme could also catalyse the terminal desaturation step, i.e. the desaturation of 24-carbon highly unsaturated fatty acids, has never been elucidated. To test this hypothesis, the activity of rat Delta6-desaturase expressed in COS-7 cells was investigated. Recombinant Delta6-desaturase expression was analysed by Western blot, revealing a single band at 45 kDa. The putative involvement of this enzyme in the Delta6-desaturation of C(24:5) n-3 to C(24:6) n-3 was measured by incubating transfected cells with C(22:5) n-3. Whereas both transfected and non-transfected COS-7 cells were able to synthesize C(24:5) n-3 by elongation of C(22:5) n-3, only cells expressing Delta6-desaturase were also able to produce C(24:6) n-3. In addition, Delta6-desaturation of [1-(14)C]C(24:5) n-3 was assayed in vitro in homogenates from COS-7 cells expressing Delta6-desaturase or not, showing that Delta6-desaturase catalyses the conversion of C(24:5) n-3 to C(24:6) n-3. Evidence is therefore presented that the same rat Delta6-desaturase catalyses not only the conversion of C(18:3) n-3 to C(18:4) n-3, but also the conversion of C(24:5) n-3 to C(24:6) n-3. A similar mechanism in the n-6 series is strongly suggested.