Ves-Losada A, Brenner R R
Instituto de Investigaciones Bioquímicas de La Plata (INIBIOLP), Facultad de Ciencias Médicas, UNLP-CONICET, Argentina.
Mol Cell Biochem. 1995 Jan 26;142(2):163-70. doi: 10.1007/BF00928937.
Activity of one of the key enzymes involved in arachidonic acid (20:4 n-6) biosynthesis, the delta 5 desaturase, was found in rat liver cell nuclei. Up to now, it has been shown that the fatty acid desaturases are located exclusively in the endoplasmic reticulum. Similarly to what happens with microsomal enzyme the nuclear delta 5 desaturase enzyme was only fully active in the presence of a cytosolic factor. In this condition it reached a specific activity of 50 pmol 20:4 n-6 formed/min/mg of protein. This fact would imply that purified nuclei like purified microsomes lack a soluble cytosol factor necessary for the total desaturation reaction expression. Besides the nuclear delta 5 desaturase has an optimal pH of 7.6 and is inhibited by 1 or 10 mM KCN. Low long chain acyl-CoA synthetase activity that catalyzes the formation of 20:3 n-6-CoA, was also found in liver nuclei. This step would be essential in nuclear desaturation since when ATP and/or CoA (necessary for the acylation reaction) are omitted from the incubation mixture, the desaturation reaction does not take place.
在大鼠肝细胞核中发现了花生四烯酸（20:4 n-6）生物合成过程中涉及的一种关键酶——δ5去饱和酶的活性。到目前为止，已经表明脂肪酸去饱和酶仅位于内质网中。与微粒体酶的情况类似，核δ5去饱和酶仅在存在胞质因子的情况下才具有完全活性。在此条件下，它达到了50 pmol 20:4 n-6形成/分钟/毫克蛋白质的比活性。这一事实意味着，像纯化的微粒体一样，纯化的细胞核缺乏总去饱和反应表达所需的可溶性胞质因子。此外，核δ5去饱和酶的最适pH为7.6，并受到1或10 mM KCN的抑制。在肝细胞核中还发现了低活性的长链酰基辅酶A合成酶，该酶催化20:3 n-6-CoA的形成。这一步骤在核去饱和过程中至关重要，因为当从孵育混合物中省略ATP和/或辅酶A（酰化反应所必需的）时，去饱和反应就不会发生。
