Thanuthong T, Francis D S, Senadheera S P S D, Jones P L, Turchini G M
School of Life and Environmental Sciences, Deakin University, Warrnambool, VIC, Australia.
Lipids. 2011 Dec;46(12):1111-27. doi: 10.1007/s11745-011-3607-4. Epub 2011 Sep 4.
Five experimental diets with constant total C(18) PUFA and varying 18:3n-3/18:2n-6 ratios were fed to rainbow trout over an entire production cycle. The whole-body fatty acid balance method demonstrated a clear trend of progressively reduced fatty acid bioconversion activity along the n-3 and n-6 pathways, up to the production of 20:5n-3 and 20:4n-6, respectively. This suggests that the pathway exhibits a "funnel like" progression of activity rather than the existence of a single rate limiting step. The production of 22:5n-3 and 22:6n-3 was more active than that of 20:5n-3. However, despite this trend in reduced apparent in vivo net enzyme activity, the efficiency of the various bioconversion steps (measured as % of bioconverted substrate) confirmed an opposing trend. A 3.2-fold higher Δ-6 desaturase affinity towards 18:3n-3 over 18:2n-6 and an 8-fold greater Δ-5 desaturase affinity towards 20:4n-3 over 20:3n-6 were recorded. The main results of the study were that (1) rainbow trout are quite efficient at bioconverting 18:3n-3 to 22:6n-3, and (2) the LC-PUFA biosynthetic pathway is substrate limited. Fillet n-3 LC-PUFA concentrations increased with the increasing dietary supply of 18:3n-3. Despite an almost identical dietary supply of n-3 LC-PUFA, originating from the fish meal fraction of the diets, the fillets of trout fed the diet richest in 18:3n-3 were 2-fold higher in n-3 LC-PUFA than fish fed low 18:3n-3 diets. Nevertheless, fillets of trout fed a fish oil control diet contained more than double the amount of n-3 LC-PUFA compared to fish fed the diets richest in 18:3n-3.
在整个生产周期内，用五种总C(18)多不饱和脂肪酸（PUFA）含量恒定但18:3n-3/18:2n-6比例不同的实验饲料喂养虹鳟鱼。全身脂肪酸平衡法显示，沿着n-3和n-6途径，脂肪酸生物转化活性呈逐渐降低的明显趋势，分别直至生成20:5n-3和20:4n-6。这表明该途径呈现出一种“漏斗状”的活性变化进程，而非存在单一的限速步骤。22:5n-3和22:6n-3的生成比20:5n-3更活跃。然而，尽管体内表观净酶活性呈现降低趋势，但各种生物转化步骤的效率（以生物转化底物的百分比衡量）却呈现相反趋势。记录到Δ-6去饱和酶对18:3n-3的亲和力比对18:2n-6高3.2倍，以及Δ-5去饱和酶对20:4n-3的亲和力比对20:3n-6高8倍。该研究的主要结果为：（1）虹鳟鱼在将18:3n-3生物转化为22:6n-3方面相当高效；（2）长链多不饱和脂肪酸（LC-PUFA）生物合成途径受底物限制。鱼肉中n-3 LC-PUFA浓度随饲料中18:3n-3供应量的增加而升高。尽管饲料中源自鱼粉部分的n-3 LC-PUFA供应量几乎相同，但喂食富含18:3n-3饲料的虹鳟鱼的鱼肉中n-3 LC-PUFA含量比喂食低18:3n-3饲料的鱼高2倍。然而，与喂食富含18:3n-3饲料的鱼相比，喂食鱼油对照饲料的虹鳟鱼的鱼肉中n-3 LC-PUFA含量是其两倍多。
