Henderson R J, Burkow I C, Buzzi M, Bayer A
NERC Unit of Aquatic Biochemistry, Department of Biological and Molecular Sciences, University of Stirling, Stirling FK9 4LA, Scotland,
Biochim Biophys Acta. 1998 Jun 15;1392(2-3):309-19. doi: 10.1016/s0005-2760(98)00045-9.
The effects of long chain n-3 polyunsaturated fatty acids (PUFA) on the desaturation and elongation systems involved in the conversion of 18:3n-3 to 24:6n-3 were investigated. Microsomes were prepared from the livers of rainbow trout and incubated with 14C-labelled 18:3n-3 and cofactors required for elongation and/or desaturation in the presence of 22:6n-3, 24:5n-3 or 24:6n-3. The formation of 24:6n-3 was significantly inhibited in the presence of 50 microM 22:6n-3, 24:5n-3 or 24:6n-3, whereas the amount of radiolabelled 20:5n-3 formed was inhibited by only 24:5n-3 or 24:6n-3 at the same concentration. When malonyl-CoA was omitted from the incubation system to allow the measurement of desaturation in the absence of elongation, the Delta6 desaturation of 14C-18:3n-3 to 14C-18:4n-3 was inhibited by approximately 25% in the presence of 24:5n-3 or 24:6n-3 but was not affected by 22:6n-3. The Delta5 desaturation of 14C-20:4n-3 was not affected by the presence of any of the long chain PUFA and no significant effect of 18:3n-3, 22:6n-3 or 24:6n-3 on the Delta6 desaturation of 24:5n-3 to 24:6n-3 was observed. To permit the measurement of individual elongation reactions, KCN was included in the incubation medium to inhibit desaturation and 14C-labelled 18:3n-3, 18:4n-3, 20:4n-3, 20:5n-3 and 22:5n-3 were examined as substrates. 18:4n-3 and 22:5n-3 were more extensively used for elongation than 18:3n-3, 20:4n-3 and 20:5n-3. The presence of 22:6n-3, 24:5n-3 or 24:6n-3 in the incubation system had no effect on any of the specific elongations of any of the substrates examined. It is concluded that, in the conversion of 18:3n-3 to 24:6n-3 by trout liver microsomes, the Delta6 desaturation of 18:3n-3 may be subjected to direct feedback inhibition and that 24:5n-3 may be preferred over 18:3n-3 as a substrate for Delta6 desaturation.
研究了长链n-3多不饱和脂肪酸（PUFA）对参与18:3n-3转化为24:6n-3的去饱和及延长系统的影响。从虹鳟鱼肝制备微粒体，并在22:6n-3、24:5n-3或24:6n-3存在的情况下，与14C标记的18:3n-3以及延长和/或去饱和所需的辅因子一起孵育。在存在50 microM 22:6n-3、24:5n-3或24:6n-3时，24:6n-3的形成受到显著抑制，而在相同浓度下，形成的放射性标记20:5n-3的量仅受到24:5n-3或24:6n-3的抑制。当从孵育系统中省略丙二酰辅酶A以在无延长的情况下测量去饱和时，在24:5n-3或24:6n-3存在下，14C-18:3n-3向14C-18:4n-3的Δ6去饱和受到约25%的抑制，但不受22:6n-3影响。14C-20:4n-3的Δ5去饱和不受任何长链PUFA存在的影响，并且未观察到18:3n-3、22:6n-3或24:6n-3对24:5n-3向24:6n-3的Δ6去饱和有显著影响。为了能够测量各个延长反应，在孵育培养基中加入KCN以抑制去饱和，并将14C标记的18:3n-3、18:4n-3、20:4n-3、20:5n-3和22:5n-3作为底物进行检测。与18:3n-3、20:4n-3和20:5n-3相比，18:4n-3和22:5n-3更广泛地用于延长。孵育系统中22:6n-3、24:5n-3或24:6n-3的存在对所检测的任何底物的任何特定延长均无影响。得出的结论是，在虹鳟鱼肝微粒体将18:3n-3转化为24:6n-3的过程中，18:3n-3的Δ6去饱和可能受到直接反馈抑制，并且24:5n-3可能比18:3n-3更适合作为Δ6去饱和的底物。
